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1704 Views 4 Replies Latest reply: Jun 29, 2011 3:43 PM by Brian RSS

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EIGRP Neighbourship

Jun 29, 2011 9:03 AM

Kamalpreet 21 posts since
Jun 6, 2011

I assign secondary IP of f0/0 on both R1 and R2. on R2 i publish network 10.0.0.0, 3.0.0.0, 2.0.0.0. Still router is able to create neighbourship as i have not publish 192.168.1.1 network on R2.


why this happen.

 

 

R1

 

interface Loopback0

ip address 1.1.1.1 255.255.255.0

!

interface FastEthernet0/0

ip address 10.1.1.1 255.255.255.0 secondary

ip address 192.168.1.1 255.255.255.0

duplex auto

speed auto

!

router eigrp 1

network 0.0.0.0

no auto-summary

!

no ip http server

 

 

 

R2

 

interface Loopback0

ip address 2.2.2.3 255.255.255.0 secondary

ip address 2.2.2.2 255.255.255.0

!

interface Loopback3

ip address 3.3.3.3 255.255.255.0

!

interface FastEthernet0/0

ip address 10.1.1.2 255.255.255.0 secondary

ip address 192.168.1.2 255.255.255.0

duplex auto

speed auto

!

router eigrp 1

network 2.2.2.0 0.0.0.7

network 3.0.0.0

network 10.0.0.0

no auto-summary

  • Currently Being Moderated
    1. Jun 29, 2011 1:55 PM (in response to Kamalpreet)
    Re: EIGRP Neighbourship

    in your case R1 you all networks subnets published using 0.0.0.0, means primary address and secondary over R1, where as over R2 you publish only Secondary)

     

    Let's take a look at R2 and R3, which will be using secondary addresses to form an EIGRP adjacency across an ethernet segment.

     

    R2(config)#interface ethernet0

    R2(config-if)#ip address 172.12.23.2 255.255.255.0

    R2(config-if)#ip address 23.23.23.2 255.255.255.0 secondary

    R2(config)#router eigrp 100

    R2(config-router)#no auto-summary

    R2(config-router)#network 23.23.23.0 0.0.0.255          (publised secondary only)

     

     

    R3(config)#interface ethernet0

    R3(config-if)#ip address 172.12.23.3 255.255.255.0

    R3(config-if)#ip address 23.23.23.3 255.255.255.0 secondary

    R3(config)#router eigrp 100

    R3(config-router)#no auto-summary

    R3(config-router)#network 23.23.23.0 0.0.0.255

     

     

    Here's the partial output of show ip eigrp neighbor on R3:

     

     

    R3#show ip eigrp neighbor

     

    IP-EIGRP neighbors for process 100

     

    H Address Interface

     

     

    0 172.12.23.2 Et0

     

    The adjacency has formed! Note the address is actually the primary IP address on the interface, even though we used the secondary network number in the EIGRP network command. Personally, I stay away from secondary network numbers if at all possible, but you should know that secondary IP addresses can be used to create EIGRP adjacencies.

     

    Note: common error with using secondary addresses comes when an address from the same subnet is the primary interface address on one neighbor and the secondary interface address on another.

     

    Let's say we had configured R2 and R3 as follows:

     

    R2(config)#int e0

     

    R2(config-if)#ip address 23.23.23.2 255.255.255.0

     

     

    R3(config)#interface ethernet0

     

    R3(config-if)#ip address 172.12.23.3 255.255.255.0

     

    R3(config-if)#ip address 23.23.23.3 255.255.255.0 secondary

     

     

    On R2, we get this message:

     

     

    01:54:05: IP-EIGRP: Neighbor 172.12.23.3 not on common subnet for Ethernet0 (23.23.23.2 255.255.255.0)

     

     

    Since we configured 23.23.23.2 as a primary interface address on R2, the EIGRP process is looking at the primary interface address on potential neighbors. R3's primary ethernet0 address is 172.12.23.2, so you get the 'not on common subnet' error message - and what you don't get is an adjacency! That's something to be aware of on your 642-901 BSCI exam as well as when working with EIGRP in production networks.

     

     

    vist this link for further details

    http://www.flixya.com/blog/356218/Cisco-CCNP-642-901-BSCI-Exam-Tutorial-EIGRP-Adja

  • Brian 2,971 posts since
    Aug 17, 2009
    Currently Being Moderated
    2. Jun 29, 2011 3:22 PM (in response to Kamalpreet)
    Re: EIGRP Neighbourship

    bottom line, EIGRP can not form neighbor adjacencies over secondary IP addresses.

     

    HTH

  • Currently Being Moderated
    3. Jun 29, 2011 3:30 PM (in response to Brian)
    Re: EIGRP Neighbourship

    neighbors adjacencies can be possible using secondary shows link as made by primary IP, and may have some issues in this case

  • Brian 2,971 posts since
    Aug 17, 2009

    No, EIGRP will not form neighbor adjacencies over secondary addresses.  Check your configuration again.  This is from the EIGRP FAQ.

     

    EIGRP does support secondary addresses. Since EIGRP always sources data packets from the primary address, Cisco recommends that you configure all routers on a particular subnet with primary addresses that belong to the same subnet. Routers do not form EIGRP neighbors over secondary networks. Therefore, if all of the primary IP addresses of routers do not agree, problems can arise with neighbor adjacencies.

     

    HTH

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