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CCNA Certification: WAN Concepts

March 2nd, 2010 by CiscoKits

Cisco CCNA Certification: WAN Concepts

We are welcoming you to a new lesson from our Cisco CCNA 640-802 exam preparation series. As outlined in the CCNA exam requirements, the CCNA candidate must have at least a basic understanding about WANs.

Wide Area Networks, or WANs for short, is a network that operates beyond the geographic scope of a LAN. A LAN is used to connected computers and network devices in a small geographic area, while WANs are extending to larger geographical areas. For example, you have one office located in USA and another office located in London. It would be impossible to create a LAN network between these two offices, but bigger services providers or carriers can be able to connect these two offices for you using WAN technologies. To operate, WANs use serial connections of various types.

WANs operate at OSI Layer 1 and Layer 2, specifically the Physical Layer and the Data Link Layer. To review, OSI Layer 1 describes how to provide electrical, mechanical and operational connections, while Layer 2 defines how data is encapsulated for transmission to a remote location and the mechanisms for transferring the resulting frames. Different technologies are used, such as Frame Relay and ATM. WAN access standards are defined and managed by a number of recognized authorities like, International Organization of Standardization (ISO), Telecommunication Industry Association (TIA) and Electronic Industries Alliance (EIA).

When you prepare for the CCNA exam, you must be able to describe some specific WAN terms. Some terms are related to the Physical Layer, some to the Data Link Layer and some about the WAN Switching methods. In this lesson we will discuss the terms related to the Physical Layer and the ones related to WAN Switching. The Data Link layer, specifically the encapsulation types and frame formats will be left for another lesson.

At the Physical Layer of a WAN you must be able to recognize and describe some key concepts:

  • Customer Premises Equipment (CPE) – is the device located in the premises of the subscriber (company) and connected to a service provider or carrier. The subscriber can either own or lease the equipment from the carrier. Example of CPE equipments are telephones, DSL and Cable modems, set-top boxes.
  • Data Communications Equipment (DCE) – sometimes called data circuit-terminating equipment, the DCE provides an interface to connect subscribers to the WAN cloud and consists of devices that put data on the local loop. Usually, the DCE equipment is a modem.
  • Data Terminal Equipment (DTE) – are the customer devices that pass the data from its network for transmission over the WAN. The DTE connects to the local loop through the DCE. The DTE device is usually a router.
  • Demarcation Point – is the border which separates the customer equipment from the service provider equipment. Physically, the Demarcation Point is usually the cabling junction box from the customer premises.
  • Local Loop – is the copper or fiber cable that connects the CPE at the subscriber to the Central Office (CO) of the service provider. Sometimes is called “last-mile”.
  • Central Office (CO) – is the service provider’s facility where local telephone cables link to long-haul, all-digital, fiber-optic communications lines through a system of switches and other equipments.

Several types of devices are used in WANs:

  • Modem – used to modulate an analog carrier signal to encode digital information and also demodulate the carrier signal to decode the transmitted information.
  • CSU/DSU – used by digital lines such as T1 or T3. The CSU provides termination for the digital signal and the DSU converts the line frames so the LAN can interpret them and vice versa.
  • WAN Switch – is a multiport internetworking device used by carriers able to switch WAN traffic types such as Frame Relay, ATM or X.25. They operate at the Data Link Layer.
  • Router – provides internetworking and WAN access interface ports used to connect to the service provider network, such as serial interfaces. Some types of interfaces require an external device such as a DSU/CSU or modem (analog, cable, DSL).
  • Core Router – is the router located in the middle or backbone of the WAN. The router must be able to support multiple types of interfaces and must be able to forward IP packets at full speed on those interfaces. The router must also support the routing protocols used in the core.

As we already told you, several authorities are handling the WAN standards. These protocols establish the codes and electrical parameters used by devices to communicate with each other. We will cover the most important ones, as requested by the Cisco CCNA exam.

  • EIA/TIA-232 – this protocol is able to signal speeds of up to 64kb/s using a 25-pin D-connector over short distances. It is also known as RS-232. The ITU-T V.24 specification is effectively the same.
  • EIA/TIA-449/530 – this is the faster version of EIA/TIA-232, being able to carry frames at speeds up to 2Mb/s. It uses a 36-pin D-connector and is also able to reach longer destinations. Also know as RS422 and RS-423.
  • EIA/TIA-612/613 – describes the High-Speed Serial Interface (HSSI) protocol, which provides speeds up to 52Mb/s using a 60-pin D-connector.
  • V.35 – ITU-T standard for synchronous connections between a network access device and a packet network using a 34-pin rectangular connector. Originally designed to support speeds up to 48kb/s, now supports speeds of up to 2.048Mb/s.
  • X.21 – ITU-T standard for synchronous digital communications. Uses a 15-pin D-connector.

WAN protocols are not able to run over LAN technologies, such as Ethernet and vice versa because the frame formats, encapsulation methods and the signaling at the physical layer differ from WAN to LAN.

WAN connections are generally grouped in three connection types: Point-to-Point, Circuit-switched and Packet-switches. In your preparation for the CCNA exam you must study Circuit-switched and Packet-switched technologies.

Circuit-switched networks are networks that are establishing a dedicated circuit between nodes and terminals before users may communicate. Let’s take for example a connection between two modems. The first one tries to make a connection with the other one by dialing its number. The dialed number is used to set the switches in the exchanges along the route of the call so that there is a continuous circuit between the two modems. However, the internal path between the exchanges is shared with a number of other connections. Time-division multiplexing (TDM) assures that a fixed capacity is allocated to each connection. Examples of Circuit-switched networks are the Public Switched Telephone Network (PSTN) and Integrated Services Digital Network (ISDN).

Packet-switched networks, unlike circuit-switched, route packets over a shared network. They do not require a circuit to be established and they allow multiple devices to communicate over the same channel. The switches are able to determine the link required to be used for forwarding the packet to the next switch or device using the addressing information found in each packet. The link determination can be made in two ways: connectionless or connection-oriented. Connectionless systems carry full addressing information in each packet and each switch must evaluate the address to be able to figure out where to send it, while connection-oriented systems are able to predetermine the route for a packet and each packet carries only an identifier. In packet switched networks, because the internal links are shared by many users, you may encounter delays and jitter (variability of delay).

The predetermined routes in a packet-switched network are called virtual circuits (VCs). A VC is a logical circuit between two network devices through the shared internal network. There are two types of VCs:

  • Permanent Virtual Circuit (PVC) – PVCs are used when data transfer between devices is constant.
  • Switched Virtual Circuit (SVC) – is an on-demand VC. The virtual circuit comes up when a data transfer begins and terminates when the transfer is complete. The first phase in a SVC is to establish the VC itself and then the data transfer begins. When the transfer completes, the VC disconnects from the remote device. SVCs are cheaper than PVCs.

Examples of packet-switched connections include: X.25, Frame Relay and ATM.

We will go deeper in this CCNA topic by studying different circuit-switched and packet-switched connections.

Analog dialup and ISDN are examples of circuit switched connections.

Analog dialup is using the traditional telephony copper cables. The data is modulated and demodulated by a modem and sent through the local loop to the CO. Advantages of using analog dialup are simplicity, available and low implement costs, but the main disadvantage is the low data rate, 56kb/s due to the PSTN network limitations. If your company needs a data connection only occasionally and is not sending or receiving large amounts of data, this connection may be adequate. However, voice and video traffic is not supposed to work at these lot bit rates.

Integrated Services Digital Network, or ISDN for short, are also circuit-switched networks. They allow a local loop to carry digital signals, resulting in higher data rates. ISDN turns the analog signals to time-division multiplexed (TDM) digital signals. TDM allows two or more signals to be transferred as subchannels in one communication channel. ISDN connections are using 64kb/s bearer channels (B) for voice or data and a signaling delta channel (D) for call setup and other purposes.

There are two types of ISDN interfaces:

  • Basic Rate Interface (BRI) – provides two 64 kb/s B channels and a 16kb/s D channel.
  • Primary Rate Interface (PRI) – allows for higher speeds. In North America, an ISDN PRI deliver 23 B channels at 64kb/s and one D channel, also at 64kb/s, totaling to 1.544MB/s, corresponding to a T1 connection. In the other parts of the world, PRI provides 30 B channels and one D channel, totaling to 2.048MB/s, corresponding to an E1 or a J1 connection.

Common packet-switched technologies used today include X.25, Frame Relay and ATM.

X.25 is a packet-switched technology mainly used these days for point-of-sale (POS) card readers. X.25 works at the Network Layer. Subscribers are provided with a network address. SVCs are established using call request packets and are identified using a channel number. Available speeds vary from 2400b/s to 2Mb/s, but they rarely exceed above 64kb/s. Due to the speed limitations, this type of networks are now being replaced by other technologies such as Frame Relay, ATM and ADSL.

Frame Relay is a protocol that works at the Data Link Layer, implementing flow control. Frame relay offers speeds up to 4Mb/s, and is able to carry both voice and data traffic. The VCs in Frame Relay are identified using an unique DLCI. You will find more details about Frame Relay in its dedicated lesson.

Asynchronous Transfer Mode (ATM) has a cell-based architecture. You may find someone referring to ATM as a cell-switched network. ATM cell are always 53 bytes, containing a 5 byte ATM header followed by 48 bytes of ATM payload. ATM networks are suitable for voice, video and data traffic. However, due to its small cells, it’s is less efficient than X.25 and Frame Relay and you need at least 20% more bandwidth than Frame Relay to carry the same amount of data. The biggest advantage of ATM is that it is able to operate at very high speeds – from T1/E1 to OC-12 (622Mb/s) and higher. In most cases, ATM uses PVCs, but can be configured as a SVCs too and allows multiple VCs on a single leased-line connection.

This concludes our lesson today. We hope you find it useful in your preparation for the CCNA exam. Understanding these key WAN concepts is very important, as well as for taking the CCNA certification but for real-life scenarios too.

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CiscoKits CCNA Security 640-553 Lab Workbook Download!

February 20th, 2010 by CiscoKits

Today is going to be a real short post introducing the ability to download our brand new CCNA Security 640-553 Lab Workbook in eBook format. We have had many customers who do not want to wait for a physical copy to arrive via UPS. I understand that as you want to get to doing your CCNA Security labs as quickly as possible. So we are offering a solution in which you can purchase to download our CCNA Security 640-553 Lab Workbook. You can review the contents of the CCNA Security Lab Workbook here are our store at this link:

http://www.ciscokits.com/ccna-security-640-553-workbook/

CiscoKits CCNA Security 640-553 Lab Workbook Download!

One of the nice things about the download version, is that you can download the CCNA Security Lab Workbook and preview some of the chapters FREE that are not password protected. If you like it, you can purchase a license to unlock the entire CCNA Security Lab Workbook.

So without further ado, here is the link to the electronic version of our CCNA Security Lab workbook

http://www.ciscokits.com/ebooks/CiscoKits-CCNA-Security-640-553-Lab-Workbook.zip

We hope you enjoy this new offering from CiscoKits assisting in your CCNA Security exam studies!

slabworkbook

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Cisco Certification 640-802: Open Shortest Path First – OSPF Part II

February 12th, 2010 by CiscoKits

Cisco Certification 640-802: Open Shortest Path First – OSPF Part II

Now on to part II of our CCNA certification topic of OSPF.

OSPF however, can be a challenge in Multiaccess Networks. Creating adjacencies for every two routers in your network can result to a great number of unnecessary adjacencies and this leads to LSA flooding. To better understand the result, the formula to figure out how many adjacencies will be creating in this scenario is (n stands for the number of routers): n(n-1)/2. Making the calculations for a 5 router scenario this gives us 10. That’s not that much, but let’s do the math for 20 routers: 20(20-1)/2 = 190. Now try to imagine what’s happening when the routers are sending out LSAs. The solution for this problem is to elect a Designated Router (DR).

 

Designated Routers (DR) is a router elected to distribute the LSAs. This way, large scale networks can avoid LSA floods. After the election of the DR a Backup Designated Router (BDR) is also elected, in case of DR failure. With a DR present in your network, the other routers, instead of flooding LSAs around the network, they only send them to the DR and the BDR using the multicast address 224.0.0.6 ( also known as ALLDRouters). After the DR receives the LSA, it sends it to the other routers in the network using the 224.0.0.5 (also known as ALLSPFRouters).

               

The election process is a fairly simple one. The DR is the router with the highest OSPF interface priority, the BDR is the one with second highest OSPF interface priority. If their interface priorities are equal, the router with the highest router ID wins. The show ip ospf neighbor command shows the status of the routers.

 

Router# show ip ospf neighbor                                                      

                                                                                

   ID          Pri   State        Dead Time     Address         Interface       

10.199.199.137  1    FULL/DR       0:00:31    192.168.80.37      Ethernet0       

172.16.48.1     1    FULL/DROTHER  0:00:33    172.16.48.1        Fddi0          

172.16.48.200   1    FULL/DROTHER  0:00:33    172.16.48.200      Fddi0           

10.199.199.137  5    FULL/DR       0:00:33    172.16.48.189      Fddi0          

 

The DR router should be a powerful one to handle it’s job. In almost every network you will see many models, some newer, some older. To make sure the router you want will become DR, you can manually set the priority with the ip ospf priority priority interface command (priority is between 0 and 255).

 

In some cases you may find that the update interval of Hello and Dead packets it’s not appropriate for your network. In this case you can adjust them with the ip ospf hello-interval seconds and ip ospf dead-interval seconds interface commands.

 

One of the must-have skills for every network administrator is the ability to use the show commands. Every time when you are in doubt about the good operation of your OSPF network, the show ip ospf command is here to assist you. To check if two routers have become neighbors, you must use the show ip ospf neighbors command. Also, show ip ospf interface interface-name will give you information about Hello and Dead times.

 

 

1)   show ip protocols

 

Router#show ip protocols                                                        

                                                                                   

Routing protocol is “ospf 1”                                                       

  Outgoing update filter list for all interfaces is not set                       

  Incoming update filter list for all interfaces is not set                          

  Router ID 192.168.0.1                                                         

  Number of areas in this router is 1. 1 normal 0 stub 0 nssa                   

  Maximum path: 4                                                               

  Routing for Networks:                                                         

    192.168.0.0 0.0.0.255 area 0                                                 

    10.0.0.0 0.0.0.31 area 0                                                    

  Reference bandwidth unit is 100 mbps                                          

    Routing Information Sources:                                                

      Gateway         Distance     Last Update                                  

      192.168.0.2          110     11:29:29                                     

      10.0.0.2             110     11:29:29                                     

    Distance: (default is 110)                                                  

 

2)   show ip ospf

 

Router# show ip ospf                                                              

                                                                                

Routing Process “ospf 1″ with ID 192.168.0.1                                    

 Supports only single TOS(TOS0) routes                                          

 Supports opaque LSA                                                            

 Supports Link-local Signaling (LLS)                                            

 Initial SPF schedule delay 5000 msecs                                           

 Minimum hold time between two consecutive SPFs 10000 msecs                     

 Maximum wait time between two consecutive SPFs 10000 msecs                     

 Incremental-SPF disabled                                                        

 Minimum LSA interval 5 secs                                                     

 Minimum LSA arrival 1000 msecs                                                  

 LSA group pacing timer 240 secs                                                 

 Interface flood pacing timer 33 msecs                                           

 Retransmission pacing timer 66 msecs                                           

 Number of external LSA 0. Checksum Sum 0×0                                      

 Number of opaque AS LSA 0. Checksum Sum 0×0                                    

 Number of DCbitless external and opaque AS LSA 0                               

 Number of DoNotAge external and opaque AS LSA 0                                 

 Number of areas in this router is 0. 0 normal 0 stub 0 nssa                     

 External flood list length 0                                                    

     Area BACKBONE(0)                                                             

         Number of interfaces in this area is 2                                 

         Area has message digest authentication                                 

         SPF algorithm executed 4 times                                          

         Area ranges are                                                        

         Number of LSA 4. Checksum Sum 0×29BEB                                  

         Number of opaque link LSA 0. Checksum Sum 0×0                           

         Number of DCbitless LSA 3                                              

         Number of indication LSA 0                                             

         Number of DoNotAge LSA 0                                               

         Flood list length 0                                                     

 

3)   show ip ospf interface interface-name

 

Router# show ip ospf interface ethernet 0                                          

                                                                                  

Ethernet 0 is up, line protocol is up                                                

Internet Address 192.168.0.202, Mask 255.255.255.0, Area 0.0.0.0                 

AS 201, Router ID 192.168.0.1, Network Type BROADCAST, Cost: 10                  

Transmit Delay is 1 sec, State OTHER, Priority 1                                   

Designated Router id 192.168.0.10, Interface address 192.168.0.10                

Backup Designated router id 192.168.0.28, Interface addr 192.168.0.28             

Timer intervals configured, Hello 10, Dead 60, Wait 40, Retransmit 5            

Hello due in 0:00:05                                                             

Neighbor Count is 8, Adjacent neighbor count is 2                                

  Adjacent with neighbor 192.168.0.28  (Backup Designated Router)                 

  Adjacent with neighbor 192.168.0.10  (Designated Router)                      

 

Every OSPF route in show ip route has an O at the beginning like in the following example:

 

Router# show ip route                                                                   

                                                                                  

Codes: I – IGRP derived, R – RIP derived, O – OSPF derived,                       

       C – connected, S – static, E – EGP derived, B – BGP derived,               

       * – candidate default route, IA – OSPF inter area route,                    

       i – IS-IS derived, ia – IS-IS, U – per-user static route,                    

       o – on-demand routing, M – mobile, P – periodic downloaded static route,     

       D – EIGRP, EX – EIGRP external, E1 – OSPF external type 1 route,           

       E2 – OSPF external type 2 route, N1 – OSPF NSSA external type 1 route,   

       N2 – OSPF NSSA external type 2 route                                       

                                                                                 

Gateway of last resort is 10.119.254.240 to network 10.140.0.0                                                                                                   

O E2 172.150.0.0 [160/5] via 10.119.254.6, 0:01:00, Ethernet2                     

E    172.17.10.0 [200/128] via 10.119.254.244, 0:02:22, Ethernet2                

O E2 172.70.132.0 [160/5] via 10.119.254.6, 0:00:59, Ethernet2                   

O E2 10.130.0.0 [160/5] via 10.119.254.6, 0:00:59, Ethernet2                       

E    172.30.0.0 [200/128] via 10.119.254.244, 0:02:22, Ethernet2                     

If OSPF is not correctly configured, you, as a network administrator, should be able to figure out what’s missing or what’s the reason it doesn’t work from the output of the show commands. Study the output of these commands carefully in a working environment. Try to break something, study the output again and compare it with the one before. This way you will be able to recognize errors faster.

We hope you found this CCNA topic covering OSPF useful. We are proud to deliver top notch Cisco CCNA certification articles for you making your CCNA certification exam easier.

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Cisco Certification 640-802: Open Shortest Path First – OSPF Part I

January 25th, 2010 by CiscoKits

Open Shortest Path First – OSPF

Today we will talk about the OSPF dynamic routing protocol, as required for Cisco’s CCNA Exam. You should learn this protocol carefully, not only because Cisco requires a good knowledge for the CCNA certification, but you will find it in many network deployments today. From all Interior Gateway Protocols (IGPs), OSPF is probably the most common one.

OSPF (Open Shortest Path First) is probably the most widely-used Interior Gateway Protocol (IGP). The reason it became so popular is because it’s a link-state routing protocol. Link-state routing protocols are able to create the topology of your network by gathering information from all the other routers. By having the map of your network, the link-state protocol is able to select the best path to any destination in your network. Unlike distance vector routing protocols, link-state routing protocols are not sending periodic updates(this is an important CCNA concept to know), instead, after the network has converged, they advertise updates only when the topology changes. Having this behavior, OSPF is able to recalculate the routes very fast in case the topology changes or a link is failing.  This is definately a concept you want to memorize for your CCNA exam as you will definatley see it on your Cisco certification exam.
 
As defined by RFC 2328, OSPF is using an arbitrary value called cost for its metric. Cisco decided to use bandwidth as the OSPF cost metric.
 
OSPF’s advantages are its fast convergence and its scalability, which allows for large network scenarios. Currently, OSPFv2 is used for IPv4 networks and OSPFv3 for IPv6 networks. OSPF also supports Variable-Length Subnet Masking (VLSM) and Classless Inter-Domain-Routing (CIDR).
 
OSPF uses areas to manage the network. Areas are 32-bit numbers. Those numbers can either be in decimal form or in octet-based dot-decimal notation, just like IPv4 addresses. Area 0 (or 0.0.0.0) represents the backbone of an OSPF network.

The OSPF package header is included in every OSPF packet. In the IP packet header, the protocol field is set to 89 and the destination address is set to the ALLSPFRouters address, 224.0.0.5.

The OSPF protocol is sending the following packet types which will be covered on your CCNA 640-802 exam:
1. Hello – used to discover the neighbors, establish the parameters on which the routers must agree, build adjacencies, elect Designated Router (DR) and Backup Designed Router (BDR).
2. DBD – Database Description is used to check if the database is synchronized between the sending and the receiving router.
3. LSR – Link-State Request is used to request specific link-state records.
4. LSU – Link-State Update packets are used to reply to LSRs and also to announce new informations or changes to the current topology.
5. LSAack – Link-State Acknowledgement is send by the receiving router to confirm the receipt of an LSU.

OSPF uses the Dijkstra’s shortest path first alhorithm (SPF) to create the SPF tree.

The default Administrative Distance is 110, which makes OSPF preferred over other IGPs, like IS-IS and RIP.

To protect your network routers from receiving unsolicited and bogus OSPF information, the protocol is able to encrypt and authenticate the routing information. This way, the routers will receive information only from routers configured with the same authentication information.

To enable OSPF on a router, you must enter router ospf process-id in the global configuration mode, where process-id is a number between 1 and 65535. This number does not have to be the same on all routers and can be randomly selected. Its influence takes place only locally and it’s not advertised on the network.
 
To announce a route through OSPF, the network network-address wildcard-mask area area-id command is used in router configuration mode. For example, to announce the network 192.168.0.0/24 you must enter network 192.168.0.0 0.0.0.255 area 0. The wildcard mask is calculated by subtracting the netmask from  255.255.255.255. For example, the wildcard mask for 255.255.255.224 is 0.0.0.31.

Router(config)#router ospf 1                                                    
Router(config-router)#network 192.168.0.0 0.0.0.255 area 0                          
Router(config-router)#network 10.0.0.0 0.0.0.31 area 0                          

OSPF has 3 methods to determine the router-id in the following order: 1) use the IP address configured with the router-id command; 2) use the highest IP address of any Loopback interface; 3) use the highest IP of any other interface. If you didn’t configure the router ID, you can find out which one is it with the show ip protocols command. However, if the Router ID is automatically assigned and you decide to change it with the router-id command, you must use the clear ip ospf process command. Please note that, if you decide to use a Loopback or a physical interface, the above command may not work and you may have to reload your router.

Router(config)#router ospf 1                                                      
Router(config-router)#router-id 192.168.0.1                                         
Router(config-router)#ctrl-Z                                                     
Router#clear ip ospf process                                                    

The metric of OSPF can be easily determined with the following formula: 10^8 / speed of the interface in bps. For example, the metric of an Ethernet interface is 10^8 / 10,000,000 bps = 10. The metric of T1 (1.544Mbps) is 10^8 / 1,544,000 bps = 64. Considering this formula, any Fast Ethernet or faster interface has a metric of 1. Also, please note that the value of the metric in OSPF from the router to a network is the accumulated value of all metrics until it reaches that network. For example, if R1 needs to get to R3 through R2, and the metric between R1 and R2 is 1 and the metric from R2 and R3 is 64, the total value of the metric is 65.
 
However, if you are using for example a serial interface, which is able to support a T1 link but you have only a 128kbps link, you must use the bandwidth or the ip ospf cost  interface command to set the appropriate value. Without it, OSPF may not be able to calculate the real cost and you may get an undesirable routing behavior.

Router(config)#interface serial 0/0/0                                             
Router(config-if)#bandwidth 128                                                 

Router(config)#interface serial 0/0/0                                           
Router(config-if)#ip ospf cost 781                                              

Of course, today’s networks have even higher speed links, and you may have for example 10GigE interfaces along with 1GigE and Fast Ethernet. The problem here is that the metric for all these interfaces will be 1 which can lead to an unexpected behavior. To solve this problem, you can adjust the reference-bandwidth (the value is in Mbits per second):

Router(config)#router ospf 1                                                    
Router(config-router)#auto-cost reference-bandwidth 10000

Please return next week to see Part II of our Cisco CCNA Certification 640-802 OSPF topic where we will be covering some of the challenges of OSPF in a multi-access environment.

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CCNA Certification 640-802: Open Shortest Path First – OSPF

January 25th, 2010 by CiscoKits

CCNA Certification: Open Shortest Path First – OSPF

 

Today we will talk about the OSPF dynamic routing protocol, as required for Cisco’s CCNA Exam. You should learn this protocol carefully, not only because Cisco requires a good knowledge for the CCNA certification, but you will find it in many network deployments today. From all Interior Gateway Protocols (IGPs), OSPF is probably the most common one.

 

OSPF (Open Shortest Path First) is probably the most widely-used Interior Gateway Protocol (IGP). The reason it became so popular is because it’s a link-state routing protocol. Link-state routing protocols are able to create the topology of your network by gathering information from all the other routers. By having the map of your network, the link-state protocol is able to select the best path to any destination in your network. Unlike distance vector routing protocols, link-state routing protocols are not sending periodic updates(this is an important CCNA concept to know), instead, after the network has converged, they advertise updates only when the topology changes. Having this behavior, OSPF is able to recalculate the routes very fast in case the topology changes or a link is failing.

               

As defined by RFC 2328, OSPF is using an arbitrary value called cost for its metric. Cisco decided to use bandwidth as the OSPF cost metric.

               

OSPF’s advantages are its fast convergence and its scalability, which allows for large network scenarios. Currently, OSPFv2 is used for IPv4 networks and OSPFv3 for IPv6 networks. OSPF also supports Variable-Length Subnet Masking (VLSM) and Classless Inter-Domain-Routing (CIDR).

               

OSPF uses areas to manage the network. Areas are 32-bit numbers. Those numbers can either be in decimal form or in octet-based dot-decimal notation, just like IPv4 addresses. Area 0 (or 0.0.0.0) represents the backbone of an OSPF network.

 

The OSPF package header is included in every OSPF packet. In the IP packet header, the protocol field is set to 89 and the destination address is set to the ALLSPFRouters address, 224.0.0.5.

 

The OSPF protocol is sending the following packet types:

1.Hello – used to discover the neighbors, establish the parameters on which the routers must agree, build adjacencies, elect Designated Router (DR) and Backup Designed Router (BDR).

2.DBD – Database Description is used to check if the database is synchronized between the sending and the receiving router.

3.LSR – Link-State Request is used to request specific link-state records.

4.LSU – Link-State Update packets are used to reply to LSRs and also to announce new informations or changes to the current topology.

5.LSAack – Link-State Acknowledgement is send by the receiving router to confirm the receipt of an LSU.

 

OSPF uses the Dijkstra’s shortest path first alhorithm (SPF) to create the SPF tree.

 

The default Administrative Distance is 110, which makes OSPF preferred over other IGPs, like IS-IS and RIP.

 

To protect your network routers from receiving unsolicited and bogus OSPF information, the protocol is able to encrypt and authenticate the routing information. This way, the routers will receive information only from routers configured with the same authentication information.

 

To enable OSPF on a router, you must enter router ospf process-id in the global configuration mode, where process-id is a number between 1 and 65535. This number does not have to be the same on all routers and can be randomly selected. Its influence takes place only locally and it’s not advertised on the network.

               

To announce a route through OSPF, the network network-address wildcard-mask area area-id command is used in router configuration mode. For example, to announce the network 192.168.0.0/24 you must enter network 192.168.0.0 0.0.0.255 area 0. The wildcard mask is calculated by subtracting the netmask from  255.255.255.255. For example, the wildcard mask for 255.255.255.224 is 0.0.0.31.

 

Router(config)#router ospf 1                                                    

Router(config-router)#network 192.168.0.0 0.0.0.255 area 0                          

Router(config-router)#network 10.0.0.0 0.0.0.31 area 0                          

 

OSPF has 3 methods to determine the router-id in the following order: 1) use the IP address configured with the router-id command; 2) use the highest IP address of any Loopback interface; 3) use the highest IP of any other interface. If you didn’t configure the router ID, you can find out which one is it with the show ip protocols command. However, if the Router ID is automatically assigned and you decide to change it with the router-id command, you must use the clear ip ospf process command. Please note that, if you decide to use a Loopback or a physical interface, the above command may not work and you may have to reload your router.

 

Router(config)#router ospf 1                                                       

Router(config-router)#router-id 192.168.0.1                                         

Router(config-router)#ctrl-Z                                                     

Router#clear ip ospf process                                                     

 

The metric of OSPF can be easily determined with the following formula: 10^8 / speed of the interface in bps. For example, the metric of an Ethernet interface is 10^8 / 10,000,000 bps = 10. The metric of T1 (1.544Mbps) is 10^8 / 1,544,000 bps = 64. Considering this formula, any Fast Ethernet or faster interface has a metric of 1. Also, please note that the value of the metric in OSPF from the router to a network is the accumulated value of all metrics until it reaches that network. For example, if R1 needs to get to R3 through R2, and the metric between R1 and R2 is 1 and the metric from R2 and R3 is 64, the total value of the metric is 65.

               

However, if you are using for example a serial interface, which is able to support a T1 link but you have only a 128kbps link, you must use the bandwidth or the ip ospf cost  interface command to set the appropriate value. Without it, OSPF may not be able to calculate the real cost and you may get an undesirable routing behavior.

 

Router(config)#interface serial 0/0/0                                             

Router(config-if)#bandwidth 128                                                 

 

Router(config)#interface serial 0/0/0                                           

Router(config-if)#ip ospf cost 781                                               

 

Of course, today’s networks have even higher speed links, and you may have for example 10GigE interfaces along with 1GigE and Fast Ethernet. The problem here is that the metric for all these interfaces will be 1 which can lead to an unexpected behavior. To solve this problem, you can adjust the reference-bandwidth (the value is in Mbits per second):

 

Router(config)#router ospf 1                                                    

Router(config-router)#auto-cost reference-bandwidth 10000        

This will conclude part 1 of our Cisco CCNA 640-802 Certification topic of OSPF.  Please come back next week to see the conclusion of this CCNA topic where we will discuss the challenges of PSPF in a mult-access environment.             

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CCNA Certification: EIGRP 640-802 Concepts

January 19th, 2010 by CiscoKits

EIGRP Concepts

In this lesson, we will introduce you to EIGRP, as requested by the Cisco CCNA certification exam.

Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco proprietary, distance vector, classless routing protocol used for routing inside a network (IGP). In addition to other distance vector routing protocol, like RIP and IGRP, EIGRP has some unique features like: Reliable Transport Protocol (RTP), which provides reliable and unreliable delivery of EIGRP packets, Bounded Updates, Diffusing Update Algorithm (DUAL) to guarantee loop-free paths and backup paths, Neighbor and Topology Tables. EIGRP can operate as a classful routing protocol, as well as a classless one.

Unlike other distance vector routing protocols, EIGRP does not send periodic updates, so the route entries to not age out, instead, EIGRP uses a lightweight Hello protocol to monitor connection status with its neighbors.

Every EIGRP packet includes the EIGRP Packet Header. The important fields in this header are the Opcode field and the Autonomous System Number field. The Opcode specifies the packet type, which can be Update, Query, Reply and Hello. The Autonomous System (AS) Number specifies the EIGRP routing process. Unlike RIP, a Cisco router can run multiple instances of EIGRP. The AS number is used to track multiple instances of EIGRP.

Reliable Transport Protocol (RTP) is used by EIGRP for the delivery and reception of EIGRP packets. RTP sends packets to either unicast address or the reserved multicast address 224.0.0.10.

As we already told you, EIGRP uses five different packet types:

·         Hello packets – are used to discover neighbors and form adjacencies with them. These packets are multicast and use unreliable delivery and are sent typically every 5 seconds.

·         Update packets – are used to propagate the routing information. Update packets are sent only when a change in the topology occurs and only to those routers who require them. EIGRP update packets use reliable delivery and are sent to the multicast address when multiple routers require them, and to the unicast address when they are required by a single router.

·         Acknowledgement (ACK) packets – are sent when reliable delivery is used. They contain a nonzero acknowledgement number and are always sent to the unicast address.

·         Query and Replay packets – are used by DUAL when searching for networks and other tasks. Queries are sent to the multicast address and use reliable delivery, while replies are sent as unicast and they are also using reliable delivery.

In EIGRP, the default administrative distance (AD) is 170 when used as an Exterior Gateway Protocol (EGP), 90 when used as an IGP and 5 for EIGRP summary routes.

EIGRP also supports authentication to ensure the information transmitted over the network is authentic and from a trusted source.

To better understand EIGRP, we will use the following topology to configure an EIGRP network.

eigrp 

First, let’s configure the IP addresses on the interfaces of the routers.

R0(config)#int Fa0/0
R0(config-if)#ip addr 172.16.1.1 255.255.255.0
R0(config-if)#no shutdown
R0(config-if)#int Fa0/1
R0(config-if)#ip addr 192.168.1.1 255.255.255.0
R0(config-if)#no shutdown

R1(config)#int Fa0/0
R1(config-if)#ip addr 172.16.1.2 255.255.255.0
R1(config-if)#no shutdown
R1(config-if)#int Fa0/1
R1(config-if)#ip addr 192.168.2.1 255.255.255.0
R1(config-if)#no shutdown

R2(config)#int Fa0/0
R2(config-if)#ip addr 192.168.1.2 255.255.255.0
R2(config-if)#no shutdown

R3(config)#int Fa0/0
R3(config-if)#ip addr 192.168.2.2 255.255.255.0
R3(config-if)#no shutdown

Now, let’s enable EIGRP and specify what networks to advertise to our neighbors. We will use EIGRP autonomous system (AS) 1.

R0(config)#router eigrp 1
R0(config-router)#network 172.16.1.0 0.0.0.255
R0(config-router)#network 192.168.1.0

Optionally, in EIGRP, you can specify the wildcard bits when you chose to advertise a network. By default, when using the network command and a classful network address such as 172.16.1.0, all interfaces will be enabled for EIGRP. Although this is not our case, if you don’t want to enable all of them, you must specify the wildcard mask. To calculate the wildcard mask, you must substract the subnet mask from 255.255.255.255. For example, the wildcard mask for 255.255.255.252 is 255.255.255.255 – 255.255.255.252 = 0.0.0.3.

Let’s continue to configure the other routers now.

R1(config-router)#router eigrp 1
R1(config-router)#network 172.16.1.0
R1(config-router)#
*Mar  1 00:14:27.267: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.1.1 (FastEthernet0/0) is up: new adjacency
R1(config-router)#network 192.168.2.0

R2(config)#router eigrp 1
R2(config-router)#network 192.168.1.0
R2(config-router)#
*Mar  1 00:16:17.475: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 192.168.1.1 (FastEthernet0/0) is up: new adjacency

R3(config)#router eigrp 1
R3(config-router)#network 192.168.2.0
R3(config-router)#
*Mar  1 00:17:02.279: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 192.168.2.1 (FastEthernet0/0) is up: new adjacency

Now, let’s check the routing table.

R3#show ip route
Codes: C – connected, S – static, R – RIP, M – mobile, B – BGP
       D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area
       N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2
       E1 – OSPF external type 1, E2 – OSPF external type 2
       i – IS-IS, su – IS-IS summary, L1 – IS-IS level-1, L2 – IS-IS level-2
       ia – IS-IS inter area, * – candidate default, U – per-user static route
       o – ODR, P – periodic downloaded static route

Gateway of last resort is not set


D    172.16.0.0/16 [90/307200] via 192.168.2.1, 00:00:35, FastEthernet0/0
D    192.168.1.0/24 [90/332800] via 192.168.2.1, 00:00:35, FastEthernet0/0
C    192.168.2.0/24 is directly connected, FastEthernet0/0

As you can see, the routing table is already populated with the routes. Let’s check the neighbors.

R0#show ip eigrp neighbors
IP-EIGRP neighbors for process 1
H   Address                 Interface       Hold Uptime   SRTT   RTO  Q  Seq
                                            (sec)         (ms)       Cnt Num
1   192.168.1.2             Fa0/1             10 00:04:27    8   200  0  4
0   172.16.1.2              Fa0/0             13 00:06:17    6   300  0  9

The fields of this command show you the following:

·         H column – lists the neighbors in the order they were learned.

·         Address – the IP address of the neighbor.

·         Interface – the local interface on which the Hello packet was received.

·         Hold – the current hold time. Every time a Hello packet is received, this value is reset to the maximum hold time for that interface and then counts down to zero. If zero is reached, the neighbor is considered down.

·         Uptime – amount of time since the neighbor was added to the neighbor table

·         SRTT (Smooth Round Trip Timer) and RT0 (Retransmit Interval ) – used by RTP to manage reliable EIGRP packets.

·         Queue Count – should always be zero, else EIGRP packets are waiting to be sent.

·         Sequence Number – used to track updates, queries and reply packets.

As with the other routing protocols, you can use the show ip protocols command to check detailed information about your routing protocols.

R0#show ip protocols
Routing Protocol is “eigrp 1”
  Outgoing update filter list for all interfaces is not set
  Incoming update filter list for all interfaces is not set
  Default networks flagged in outgoing updates
  Default networks accepted from incoming updates
  EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
  EIGRP maximum hopcount 100
  EIGRP maximum metric variance 1
  Redistributing: eigrp 1
  EIGRP NSF-aware route hold timer is 240s
  Automatic network summarization is in effect
  Automatic address summarization:
    192.168.1.0/24 for FastEthernet0/0
    172.16.0.0/16 for FastEthernet0/1
      Summarizing with metric 281600
  Maximum path: 4
  Routing for Networks:
    172.16.1.0/24
    192.168.1.0
  Routing Information Sources:
    Gateway         Distance      Last Update
    (this router)         90      00:16:06
    172.16.1.2            90      00:11:56
  Distance: internal 90 external 170

When automatic summarization is enabled or at least one subnet was learned via EIGRP, EIGRP includes a summary route. Null0 is the interface used for summary routes. This is a “virtual” interface used only for advertising purposes.

R0#show ip route
Codes: C – connected, S – static, R – RIP, M – mobile, B – BGP
       D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area
       N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2
       E1 – OSPF external type 1, E2 – OSPF external type 2
       i – IS-IS, su – IS-IS summary, L1 – IS-IS level-1, L2 – IS-IS level-2
       ia – IS-IS inter area, * – candidate default, U – per-user static route
       o – ODR, P – periodic downloaded static route


Gateway of last resort is not set

     172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
D       172.16.0.0/16 is a summary, 00:37:40, Null0
C       172.16.1.0/24 is directly connected, FastEthernet0/0
C    192.168.1.0/24 is directly connected, FastEthernet0/1
D    192.168.2.0/24 [90/307200] via 172.16.1.2, 00:33:30, FastEthernet0/0

To calculate the preferred path on a network, EIGRP uses the following values in its composite metric:

·         Bandwidth

·         Delay

·         Reliability

·         Load

The default composite formula is: metric = [K1 * bandwidth + K3*delay]

By default, K1 and K3 are set to 1, and K2, K4 and K5 are set to 0. These values can be changed with metric weights tos k1 k2 k3 k4 k5 EIGRP router configuration command.

To find out the values used by EIGRP for the bandwidth, delay, reliability and load use the show interface interface interface-number command.

R0#show interface Fa0/0
FastEthernet0/0 is up, line protocol is up
  Hardware is Gt96k FE, address is c400.039f.0000 (bia c400.039f.0000)
  Internet address is 172.16.1.1/24
  MTU 1500 bytes, BW 10000 Kbit/sec, DLY 1000 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Half-duplex, 10Mb/s, 100BaseTX/FX
  ARP type: ARPA, ARP Timeout 04:00:00

When you use Serial interfaces, the default bandwidth value may not match your real bandwidth which may cause EIGRP to not work properly. In this case, you have to manually configure the bandwidth value for your interface. Although, this is not our case, because we use FastEthernet interface, we will demonstrate you how to accomplish this, with the bandwidth kilobits interface configuration command.

R0(config)#interface Serial 0/0/0
R0(config-if)#bandwidth 1024

EIGRP is one of the most used Interior Gateway Protocols (IGP) used these days. In your preparation for your CCNA exam, you must know the basics of EIGRP and we hope you found this article useful for achieving the basic knowledge required for the CCNA certification exam. Remember that practice is best way to prepare for the CCNA exam, and we can provide you with many training resources, including labs prepared specially for the exam on which you can setup your own EIGRP enabled topologies.

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CCNA Certification 640-802: Inter-VLAN Routing

January 5th, 2010 by CiscoKits

Inter-VLAN Routing

Welcome to a new lesson from the Cisco CCNA exam preparation series. In this lesson, we will talk about Inter-VLAN routing and different methods to accomplish this. Inter-VLAN Routing is used to allow devices on separate VLANs communicate with each other.

Inter-VLAN Routing is the process of routing traffic between VLANs in a network. As we explained to you in the previous lesson about VLANs, VLANs are used to create logical networks from a physical network, isolating hosts from one VLAN from the ones in other VLANs. Most of the times, although you want to create different broadcast domain in your network by creating more logical networks, you want the hosts from those networks to communicate with each other, even if they are not belonging to the same VLAN.

A host belonging to a VLAN attached on a specific physical port, for example VLAN 10 in port FastEthernet0/10 is usually not able to communicate to a host attached to another VLAN, for example VLAN11 attached to port FastEthernet0/11. They belong to different networks, different broadcast domains and switches do not know how to forward packets from one network to another. The process of forwarding packets from a network to another is called routing and you must use a router to accomplish this.

In classic networks that are using multiple VLANs, routing is performed by connecting multiple physical interfaces on the router to multiple physical interfaces on the switch. The switch ports are connected to the router in access mode, and a different static VLAN is assigned to every interface. An access mode switch port can belong to only one VLAN and is usually used to connect to an end user device.

Usually, this is not a desired behavior because you end up using too many physical interfaces, and sooner or later you will run out of interfaces. A typical switch can have up to 48 ports. This means, you can use that switch to route traffic between VLANs for up to 48 VLANs. In smaller networks this may be enough, but in larger enterprise networks, 48 VLANs may not be enough.

“Router-on-a-stick ” is a type of router configuration in which you are able to use a single physical interface to route traffic between multiple VLANs. The router interface is configured as a trunk link and is connected to a trunk switch port. The router is accepting the tagged traffic on the trunk interface and routes it internally using subinterfaces. Trunk links are able to accept multiple VLANs on one physical interface. Switches are able to recognize the VLAN used for a specific packet through the use of encapsulation protocols that encapsulate or tag the frames. The protocols used are 802.1Q or Cisco’s proprietary Inter-Switch Link (ISL). To find out more about these encapsulation protocols check the Trunking Concepts lessons from our Cisco CCNA exam preparation series.

Subinterfaces are virtual interfaces associated with a single physical interface. These subinterfaces have their own IP address and VLAN assignment to be able to operate on a specific VLAN.

However, if your switch is capable of doing Layer 3 functions, you don’t need a router anymore. The switch will handle the Inter-VLAN routing decisions too. These switches are called multilayer switches .

The router acts as a Gateway for devices on a VLAN. The subinterface configured for a particular VLAN has an IP assigned from the range of IPs used in that VLAN. The other devices on the VLAN are sending packets for devices in other VLANs through the router. The router then, takes the routing decision and sends the packet to the destination.

Usually, when you configure a router, you assign IPs to interfaces, and once the IPs are assigned, the routing table shows how to reach the networks those IPs are part of.

Router(config)#interface Fa0/0
Router(config-if)#ip address 172.16.10.1 255.255.255.0
Router(config-if)#no shutdown
Router(config-if)#interface Fa0/1
Router(config-if)#ip address 172.16.30.1 255.255.255.0
Router(config-if)#no shutdown
Router(config-if)#end
Router#show ip route
Codes: C – connected, S – static, R – RIP, M – mobile, B – BGP
D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area
N1 – OSPF NSSA external type 1, N2 – O SPF NSSA external type 2
E1 – OSPF external type 1, E2 – OSPF external type 2
i – IS-IS, su – IS-IS summary, L1 – IS-IS level-1, L2 – IS-IS level-2
ia – IS-IS inter area, * – candidate default, U – per-user static route
o – ODR, P – periodic downloaded static route

Gateway of last resort is not set

172.16.0.0/24 is subnetted, 2 subnets
C 172.16.10.0/24 is directly connected, FastEthernet0/1
C 172.16.30.0/24 is directly connected, FastEthernet0/1

As you can see, the only chance to route traffic between those two networks is to connect both interfaces to the switch. This could be a solution if you have a small number of VLANs on your network and you are sure your network will never evolve, but if you have for example 120 VLANs what would you do?

The solution is to use subinterfaces. When you use subinterfaces,

Router(config)#interface Fa0/0.10
 Router(config-if)#encapsulation dot1q 10
Router(config-if)#ip address 172.16.10.1 255.255.255.0
Router(config-if)#interface Fa0/0.30
 Router(config-if)#encapsulation dot1q 30
Router(config-if)#ip address 172.16.30.1 255.255.255.0
 Router(config-if)#interface Fa0/0
Router(config-if)#no shutdown
Router(config-if)#end
Router#show ip route
Codes: C – connected, S – static, R – RIP, M – mobile, B – BGP
D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area
N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2
E1 – OSPF external type 1, E2 – OSPF external type 2
i – IS-IS, su – IS-IS summary, L1 – IS-IS level-1, L2 – IS-IS level-2
ia – IS-IS inter area, * – candidate default, U – per-user static route
o – ODR, P – periodic downloaded static route

Gateway of last resort is not set

172.16.0.0/24 is subnetted, 2 subnets
C 172.16.10.0/24 is directly connected, FastEthernet0/0.10
C 172.16.30.0/24 is directly connected, FastEthernet0/0.30

As you can see in this example, we use only the FastEthernet 0/0 interface for both VLANs. We have created the Fa0/0.10 and Fa0/0.30 subinterfaces, specified the encapsulation type dot1q which is IEEE’s 802.1Q, and the VLAN they belong to and we assigned an IP address. In this case, the physical interface, FastEthernet 0/0, does not need an IP address configuration, the only thing you must do is to use the no shutdown command so that the interfaces comes up.

If you use a multilayer switch, to enable to routing features you must also enable ip routing .

Switch(config)#ip routing

However, different issue may arise when you use Inter-VLAN Routing. A switch for example can have an incorrect VLAN assigned to a switch port or the switch port may be configured in access mode instead of trunk. A router also, can have the wrong VLAN assigned to an interface or subinterface or the wrong encapsulation type. Assigning an IP address belonging to a class not used in that specific VLAN will also cause Inter-VLAN routing to not function properly. If your network is not working as expected, these are the most common places to look for errors.

This concludes our lesson. When you’ll take your Cisco CCNA certification exam, you must be able to correctly configure and troubleshoot a network using Inter-VLAN Routing. Practicing is the best way to learn how things work and we hope you found our hands-on example a great starting point.

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CCNA Certification: VLAN Trunking Protocol (VTP) Part II

December 26th, 2009 by CiscoKits

When you begin to configure your VTP enabled network you must first make sure that all switches you are going to configure are set to their default settings. A good advice is to configure at least two VTP servers on your network in case one VTP server fails. Also, all switches in a VTP domain must use the same version. Not configuring the VTP version correctly will result in no VTP communication between your switches.

 

On a VTP server you must make sure you configure the following key components:

·         VTP domain

·         VTP version

·         VLANs and trunk ports

 

On the VTP clients you must configure:

·         VTP client mode

·         VTP version

·         Trunks

·         Access ports 

 

First of all, we must make sure that the VTP server’s configuration is the default one.

 

S1#show vtp status

VTP Version                     : running VTP1 (VTP2 capable)

Configuration Revision          : 0

Maximum VLANs supported locally : 1005

Number of existing VLANs        : 7

VTP Operating Mode              : Server

VTP Domain Name                 :

VTP Pruning Mode                : Disabled

VTP V2 Mode                     : Disabled

VTP Traps Generation            : Disabled

MD5 digest                      : 0xFB 0xC2 0×38 0xC1 0×0D 0×1D 0×14 0×10

Configuration last modified by 0.0.0.0 at 0-0-0 00:00:00

 

Looks good. Now, let’s configure the VTP domain name and check again the output of show vtp status.

 

S1#configure terminal

S1(config)#vtp mode server

S1(config)#vtp domain cisco

Changing VTP domain name from NULL to cisco

S1(config)#vtp version 1

VTP mode already in V1

S1(config)#exit

S1#show vtp status

VTP Version                     : running VTP1 (VTP2 capable)

Configuration Revision          : 0

Maximum VLANs supported locally : 1005

Number of existing VLANs        : 7

VTP Operating Mode              : Server

VTP Domain Name                 : cisco

 

Good. We have configured a switch to act as a version 1 VTP server for the VTP Domain cisco. Next, you must create the VLANs and trunks. You can find more details about these operations in our VLAN and Trunking courses from the CCNA Certification series.

Please note that, every added VLAN increases the revision number with 1. The name of a VLAN also increases the revision number with 1. For example, if you have 3 VLANs, you will have 3 VLANs + 3 Names = Revision 6.

 

Next, let’s configure the VTP client switches. The configuration is identical on both switches.

 

The first step is to check if the configuration is the default one with show vtp status, as you did for the VTP server too. Now let’s configure the switch to act as a client.

 

S2#configure terminal

S2(config)#vtp mode client

Setting device to VTP CLIENT mode.

S2(config)#exit

S2#show vtp status

VTP Version                     : running VTP1 (VTP2 capable)

Configuration Revision          : 0

Maximum VLANs supported locally : 1005

Number of existing VLANs        : 7

VTP Operating Mode              : Client

 

The next step is to connect the Client switch to the server. After the switches are connected, check the show vtp status output again and show vtp counters to make sure those switches are exchanging information.

 

S2#show vtp status

VTP Version                     : running VTP1 (VTP2 capable)

Configuration Revision          : 6

Maximum VLANs supported locally : 1005

Number of existing VLANs        : 10

VTP Operating Mode              : Client

VTP Domain Name                 : cisco

 

S2#show vtp counters

VTP statistics:

Summary advertisements received    : 1

Subset advertisements received     : 1

Request advertisements received    : 0

Summary advertisements transmitted : 1

Subset advertisements transmitted  : 1

 

We see that the switch has successfully joined the cisco VTP domain,  got the configuration revision 6, and now has 10 configured VLANs.

The next step is to configure the access ports, for example:

 

 

S2(config)#interface Gi0/18

S2(config-if)#switchport access vlan 20

 

In VTP enabled networks you can encounter different errors. To troubleshoot them you must be sure you the output the the show commands. Common issues you may encounter can be:

·         The VTP version is not configured correctly

·         If you use a VTP password, the password mismatches on the other switches

·         You didn’t correctly configured the VTP mode

·         You don’t have a VTP server in your network.

·         The VTP domain is not configured correctly

·         Before you put the switch on the network, you didn’t reset the revision number

 

This concludes our lesson. We are proud to provide real life examples along with our Cisco CCNA certification courses. Not only you will take the certification exam, but you will also have a valuable hands-on experience.

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CiscoKits CCNA 640-802 Lab Workbook Download!

December 7th, 2009 by CiscoKits

CiscoKits CCNA 640-802 Lab Workbook Download!

Today is going to be a real short post introducing the ability to download our CCNA 640-802 Lab Workbook.  We have had many customers who do not want to wait for a physical copy to arrive via UPS.  I understand that as you want to get to doing your CCNA labs as quickly as possible.  So we are offering a solution in which you can purchase to download our CCNA 640-802 Lab Workbook.  Keep in mind, if you purchase the electronic download copy, you will not also receive a physical copy of the book.  If you want a physical copy of the book, you will order that from our main store here http://www.ciscokits.com/cisco-ccna-lab-workbook/

One of the nice things about the download version, is that you can download the CCNA Lab Workbook and preview some of the chapters that are not password protected.  If you like it, you can buy the electronic version or the physical version.  Now the choice is yours!  So without further ado, here is the link to the electronic version of our CCNA Lab workbook  http://www.ciscokits.com/ebooks/CiscoKits-CCNA-640-802-Lab-Workbook.zip

We hope you enjoy this new offering from CiscoKits assisting in your CCNA exam studies!

labworkbook

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CCNA Certification: VLAN Trunking Protocol (VTP) Part I

November 30th, 2009 by CiscoKits

VLAN Trunking Protocol (VTP)

Welcome to a new lesson for your preparation for the CCNA certification exam. We would like to discuss today about VLAN Trunking Protocol (VTP).  We are going to again break this CCNA conept into two parts so you are not overwhemled.  VTP is very important to udnerstand completely to ensure you pass your CCNA certification exam.

VLAN Trunking Protocol (VTP) is Cisco’s proprietary protocol for managing VLAN networks. As the network grows, creating, modifying and deleting VLANs becomes a time consuming job for the newly CCNA certified administrator. VTP helps network administrators to accomplish this task in just a few minutes. The philosophy of VTP is that a router running as a VTP server should manage the VLAN configuration of the other routers on the network, called VTP clients. VTP can operate with 802.1Q as well as with ISL.

VTP can run in three different modes:

·         Server mode – in server mode you can create, remove and modify VLANs. VTP servers advertise their configuration to the VTP clients in the same VTP domain. The VLAN information is stored in NVRAM and it’s not lost after a reboot.

·         Client mode – clients only get the VLANs advertised by the VTP server. They are not able to modify, create or delete VLANs from their configuration. The VLAN configuration is not stored in NVRAM and will be lost at first reboot (of course, the switch will get the VLAN configuration back after it boots, from the VTP server)

·         Transparent mode – in this mode, the switch does not participate in the VTP domain. You are able to add, delete or modify VLANs from their configuration. The configuration of the VLANs will not be broadcasted over the network. With VTP version 2, a transparent switch is forwarding the VTP messages that he receives out its trunk ports.

 

The first thing you have to do when you begin studying VTP is to understand some key concepts. We will briefly present them to you, as requested by Cisco’s CCNA certification exam.

 

·         VTP Domain – consists of one or more interconnected switch which are sharing the same VLAN configuration. A router or a Layer 3 switch defines the boundary of a VTP domain.

·         VTP Advertisements – are used to distribute the VLAN configuration across the VTP domain.

·         VTP Modes – the modes a switch can be configured in the VTP domain, as described above.

·         VTP Server – a VTP server is used to advertise the VLAN configuration to all VTP enabled switches in the same VTP domain. This is the point where you are able to create, modify or delete the VLAN configuration.

·         VTP Client – is a VTP enabled switch which receives the VLAN information from a VTP Server. You are not able to create, modify or delete the VLAN configuration.

·         VTP Transparent – is a switches that’s not participating in the VTP domain, but forwards VTP advertisements to other switches in the network. VLANs created, modified or deleted on a transparent switch are affecting only that switch and are not broadcasted on the VTP domain.

·         VTP Pruning – By default, a switch sends broadcast, multicast and unknown unicast traffic through all trunk links. The VTP pruning increases network available bandwidth by sending traffic only on those trunk links that the traffic must use to reach the destination device.

 

When you check the VTP configuration on a switch you use the show vtp status command.

 

Switch#show vtp status

VTP Version                     : running VTP1 (VTP2 capable)

Configuration Revision          : 4

Maximum VLANs supported locally : 1005

Number of existing VLANs        : 7

VTP Operating Mode              : Server

VTP Domain Name                 :

VTP Pruning Mode                : Disabled

VTP V2 Mode                     : Disabled

VTP Traps Generation            : Disabled

MD5 digest                      : 0xFB 0xC2 0×38 0xC1 0×0D 0×1D 0×14 0×10

Configuration last modified by 192.168.1.2 at 3-1-93 00:20:31

Local updater ID is 192.168.1.2 on interface Gi0/1 (first layer3 interface found)

 

You can see here some information. The first line shows us the version of VTP the switch is running, currently 1. We can configure the switch to run VTP2 because, as you can see, it’s VTP2 capable. Next we have a configuration revision. The revision number is a 32-bit number that indicates the level of revision for a VTP frame. By default, the number is 0, and it’s incremented every time the configuration changes. We also can see that this switch is supporting 1005 VLANs configured locally, and we currently have 7 VLANs configured on the switch. We find in the next line that this switch is acting as a VTP server. The VTP Domain Name identifies the administrative domain for the switch. By default, VTP Pruning Mode, V2 Mode and Traps Generation are disabled. The MD5 digest is a 15-byte checksum of the VTP configuration.

 

VTP uses the destination MAC address 01-00-0C-CC-CC-CC, which is a reserved multicast address for VTP messages.

 

A VTP advertisement contains the following global informations:

·         VTP domain name – the name of the VTP domain

·         Updater identity and update timestamp – used by client switches to identify who sent the update and when the message was sent.

·         MD5 digest – used by client switches to compare if the checksums match. Also includes the Maximum Transmission Unit (MTU) for each VLAN.

·         Frame format – can be ISL or 802.1Q

 

Also, VTP advertisements carry the following VLAN information:

·         VLAN IDs (IEEE 802.1Q)

·         VLAN name

·         VLAN type

·         VLAN state

·         Additional VLAN configuration specific to the VLAN type

 

VTP is sending different type of advertisements:

·         Summary advertisements

o        Sent every 5 minutes by a VTP server or immediately after a configuration change has been made.

o        Informs VTP enabled switches of the current VTP configuration revision number.

·         Subset advertisements

o        Contains VLAN information.

o        Sent when you:

§         Create or delete a VLAN.

§         Suspend or activate a VLAN.

§         Change the name of a VLAN.

§         Change the MTU of a VLAN.

·         Request advertisements

o        Sent by a VTP client to a VTP server

o        Sent if:

§         The domain name has been change.

§         The switch receives a summary advertisement with a higher revision number than its own.

§         A subset message is missed.

§         The switch has been reset.

In part II of this topic, we will cover how to configure your VTP domains.  So stop back next week as we continue our Cisco CCNA certification study series.  We hope you find this information to be helpful to you in passing your CCNA exam.  If you have any suggestions on how we can improve our CCNA study series, please feel free to post your comments! :)

 

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