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This Question is Not Answered 1 Correct Answer available (4 pts) 2 Helpful Answers available (2 pts)
1292 Views 9 Replies Latest reply: Oct 5, 2011 2:22 PM by Anthony Sequeira, CCIE,VCP RSS

Currently Being Moderated

bgp in a straight line

Sep 28, 2011 2:42 AM

alef 82 posts since
Mar 19, 2011

I had a question and not sure what the best approach is (or if i understand properly).

 

If i have nodes

 

A-B-C-D

 

And they are configured similar, what should i configure to make sure routes get passed to eachother? I am

redistributing ospf igp routes from router a into bgp. All bgp nodes are connected by their interface address.

 

1. They are not in different AS, it's all ibgp.

2. I would think either a route reflector, or a confederation.

I tried to setup a confederation, with no confed peers (obviously) and i couldn't get it to work.

 

The route reflector, i couldn't get to work neither. But may i botched it up due to misunderstanding. I made router a

a router reflector (configured b,c and as clients), but i guess it only reflects, it doesn't actually passes on it's own bgp routes to neighbors.

 

Ofcourse i could make each router redistribute ospf into bgp, but i really don't want to do that. I want

to overcome the ibgp issue of a full mesh. And i've always been told that either use a route reflector or a conferation.

Maybe in hindsigh router A wasn't such a good pick :-), i guess B or C would have been better as they are partially fully meshed, but there would still

be one node that wouldn't be getting routes (A or D).

 

warm regards,

Alef

  • Anthony Sequeira, CCIE,VCP 1,008 posts since
    Nov 9, 2008
    Currently Being Moderated
    1. Sep 28, 2011 6:37 AM (in response to alef)
    Re: bgp in a straight line

    First - let's make sure you are clear on the rule that is preventing the BGP prefixes from propagating to all devices. It is the iBGP split horizon rule. A will pass the updates to B using the iBGP peering, but B will not pass the routes to C as the rule states, do not pass updates learned from one iBGP peer to other iBGP peers. As you state, a full mesh of iBGP peerings is assumed.

     

    To solve this we can do several things. The two you must absolutely master are route reflection and confederation as you mention.

     

    Let us examine route reflection here. B is receiving the updates and it is not passing them to C as a result of the split horizon rule. If we make B a route reflector and C a client, then the updates will make it to C. But then C will not pass the updates to D as a result of the darn rule again. How about we make C a reflector also and D a client? That should do the trick!

     

    Here are the relevant configurations:

    A#show run

    Building configuration...

     

     

    Current configuration : 901 bytes

    !

    version 12.4

    service timestamps debug datetime msec

    service timestamps log datetime msec

    no service password-encryption

    !

    hostname A

    !

    boot-start-marker

    boot-end-marker

    !

    !

    no aaa new-model

    memory-size iomem 5

    ip cef

    !

    !

    !

    !

    !

    multilink bundle-name authenticated

    !

    !

    !

    !

    !

    archive

    log config

      hidekeys

    !

    !

    !

    !

    !

    !

    !

    interface Loopback100

    ip address 1.1.1.1 255.255.255.0

    !

    interface FastEthernet0/0

    ip address 10.10.10.1 255.255.255.0

    duplex auto

    speed auto

    !

    interface FastEthernet0/1

    no ip address

    shutdown

    duplex auto

    speed auto

    !

    router ospf 1

    log-adjacency-changes

    network 0.0.0.0 255.255.255.255 area 0

    !

    router bgp 100

    no synchronization

    bgp log-neighbor-changes

    redistribute ospf 1

    neighbor 10.10.10.2 remote-as 100

    no auto-summary

    !

    ip forward-protocol nd

    !

    !

    ip http server

    no ip http secure-server

    !

    !

    !

    !

    !

    control-plane

    !

    !

    line con 0

    line aux 0

    line vty 0 4

    !

    !

    end

     

    B#show run

    Building configuration...

     

     

    Current configuration : 971 bytes

    !

    version 12.4

    service timestamps debug datetime msec

    service timestamps log datetime msec

    no service password-encryption

    !

    hostname B

    !

    boot-start-marker

    boot-end-marker

    !

    !

    no aaa new-model

    memory-size iomem 5

    ip cef

    !

    !

    !

    !

    !

    multilink bundle-name authenticated

    !

    !

    !

    !

    !

    archive

    log config

      hidekeys

    !

    !

    !

    !

    !

    !

    !

    interface Loopback100

    ip address 2.2.2.2 255.255.255.0

    !

    interface FastEthernet0/0

    ip address 10.10.10.2 255.255.255.0

    duplex auto

    speed auto

    !

    interface FastEthernet0/1

    ip address 11.11.11.2 255.255.255.0

    duplex auto

    speed auto

    !

    router ospf 1

    log-adjacency-changes

    network 0.0.0.0 255.255.255.255 area 0

    !

    router bgp 100

    no synchronization

    bgp log-neighbor-changes

    neighbor 10.10.10.1 remote-as 100

    neighbor 11.11.11.3 remote-as 100

    neighbor 11.11.11.3 route-reflector-client

    no auto-summary

    !

    ip forward-protocol nd

    !

    !

    ip http server

    no ip http secure-server

    !

    !

    !

    !

    !

    control-plane

    !

    !

    line con 0

    line aux 0

    line vty 0 4

    !

    !

    end

     

    C#sho run

    Building configuration...

     

     

    Current configuration : 913 bytes

    !

    version 12.4

    service timestamps debug datetime msec

    service timestamps log datetime msec

    no service password-encryption

    !

    hostname C

    !

    boot-start-marker

    boot-end-marker

    !

    !

    no aaa new-model

    memory-size iomem 5

    ip cef

    !

    !

    !

    !

    !

    multilink bundle-name authenticated

    !

    !

    !

    !

    !

    archive

    log config

      hidekeys

    !

    !

    !

    !

    !

    !

    !

    interface FastEthernet0/0

    ip address 11.11.11.3 255.255.255.0

    duplex auto

    speed auto

    !

    interface FastEthernet0/1

    ip address 12.12.12.3 255.255.255.0

    duplex auto

    speed auto

    !

    router ospf 1

    log-adjacency-changes

    network 0.0.0.0 255.255.255.255 area 0

    !

    router bgp 100

    no synchronization

    bgp log-neighbor-changes

    neighbor 11.11.11.2 remote-as 100

    neighbor 12.12.12.4 remote-as 100

    neighbor 12.12.12.4 route-reflector-client

    no auto-summary

    !

    ip forward-protocol nd

    !

    !

    ip http server

    no ip http secure-server

    !

    !

    !

    !

    !

    control-plane

    !

    !

    line con 0

    line aux 0

    line vty 0 4

    !

    !

    end

     

    D#show run

    Building configuration...

     

     

    Current configuration : 822 bytes

    !

    version 12.4

    service timestamps debug datetime msec

    service timestamps log datetime msec

    no service password-encryption

    !

    hostname D

    !

    boot-start-marker

    boot-end-marker

    !

    !

    no aaa new-model

    memory-size iomem 5

    ip cef

    !

    !

    !

    !

    !

    multilink bundle-name authenticated

    !

    !

    !

    !

    !

    archive

    log config

      hidekeys

    !

    !

    !

    !

    !

    !

    !

    interface FastEthernet0/0

    ip address 12.12.12.4 255.255.255.0

    duplex auto

    speed auto

    !

    interface FastEthernet0/1

    no ip address

    shutdown

    duplex auto

    speed auto

    !

    router ospf 1

    log-adjacency-changes

    network 0.0.0.0 255.255.255.255 area 0

    !

    router bgp 100

    no synchronization

    bgp log-neighbor-changes

    neighbor 12.12.12.3 remote-as 100

    no auto-summary

    !

    ip forward-protocol nd

    !

    !

    ip http server

    no ip http secure-server

    !

    !

    !

    !

    !

    control-plane

    !

    !

    line con 0

    line aux 0

    line vty 0 4

    !

    !

    end

     

     

    D#

     

    Anthony Sequeira

    http://stormwindlive.tv/demos.html

    Twitter: @compsolv

    Facebook: http://www.facebook.com/compsolv

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  • cadetalain 2,728 posts since
    Sep 18, 2008
    Currently Being Moderated
    2. Sep 28, 2011 6:40 AM (in response to alef)
    Re: bgp in a straight line

    Hi,

     

    Show us routing config of router A, routing table and bgp table of router A

    then bgp table of other routers when you did the the route-reflector config.

     

     

    Alain.

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  • Anthony Sequeira, CCIE,VCP 1,008 posts since
    Nov 9, 2008
    Currently Being Moderated
    4. Sep 28, 2011 7:12 AM (in response to alef)
    Re: bgp in a straight line

    Yes - confederation is also an option to get this working. This creates sub-AS systems and makes things act like eBGP peerings to get around the iBGP split horizon rule. With all due respect, you are not ready to start thinking about that yet - you have a lot of work to do on Route Reflection.

     

    Anthony Sequeira

    http://stormwindlive.tv/demos.html

    Twitter: @compsolv

    Facebook: http://www.facebook.com/compsolv

    Join this discussion now: Login / Register
  • Scott Morris - CCDE/4xCCIE/2xJNCIE 8,426 posts since
    Oct 7, 2008
    Currently Being Moderated
    5. Sep 29, 2011 5:24 AM (in response to alef)
    Re: bgp in a straight line

    Didn't work, or just didn't see any routes?

     

    iBGP has an AD of 200.  You're also running everything is OSPF, which has an AD of 110 meaning that those routes will win!

     

    "show ip bgp" should show some "r>" for RIB failure messages if you have anything exchanged correctly.  But that will tell you whether BGP itself is seeing anything!

     

    The redistribution on the first router should pass along down the line just fine, but won't really affect anything.

     

    HTH,

     

    Scott

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  • Anthony Sequeira, CCIE,VCP 1,008 posts since
    Nov 9, 2008
    Currently Being Moderated
    Re: bgp in a straight line

    Those are my configs Scott. I labbed it up quickly for the student with the point being of how the Route Reflection could be used to solve the iBGP Split Horizon rule.

     

    While quick and sloppy, the configurations demonstrate what he needs to understand.

     

    Anthony Sequeira

    http://stormwindlive.tv/demos.html

    Twitter: @compsolv

    Facebook: http://www.facebook.com/compsolv

    Join this discussion now: Login / Register
  • Scott Morris - CCDE/4xCCIE/2xJNCIE 8,426 posts since
    Oct 7, 2008
    Currently Being Moderated
    Re: bgp in a straight line

    Oh yea, so they are.   

     

    Sorry, didn't pay attention to who posted the configs!

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  • Anthony Sequeira, CCIE,VCP 1,008 posts since
    Nov 9, 2008
    Currently Being Moderated
    9. Oct 5, 2011 2:22 PM (in response to alef)
    Re: bgp in a straight line

    I recommend you start a new thread and ask a carefully phrased question you have about BGP at this point Alef. That will help us to much better help you. If you have a bunch of questions (and it appears you do), consider other threads after we fully resolve your next one.

     

    Anthony Sequeira

    http://stormwindlive.tv/demos.html

    Twitter: @compsolv

    Facebook: http://www.facebook.com/compsolv

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