CCIE Pursuit Blog

January 19, 2008

Internetwork Expert Volume II: Lab 4 – Section 11

Exterior Gateway Routing – 8 Points

11.1 BGP Peering

“The BGP peering session between r4 and r5 should remain up if r4 loses both the frame Relay and Ethernet segments to r5.”

Peer loopbacks between r4 and r5.  These routers have 3 connections between them, so if the Frame and Ethernet drop, the PTP connection will kick in.  Remember to configure ‘ebgp-multihop’ when peering loopbacks.

11.2 BGP Filtering

You need to configure r6 so that it is only advertising the routes shown in a command output to r2.

“Do not use communities, IP access-lists, or prefix-list filtering to accomplish this.”

From my output I need to filter the following routes:

*> 205.90.31.0      141.1.123.2                            0 200 254 ?
*> 220.20.3.0       141.1.123.2                            0 200 254 ?
*> 222.22.2.0       141.1.123.2                            0 200 254 ?

I should be able to filter on as path for these networks based on as_path.  Or does that count as an “ip access-list”?  IE solution guide says “go ahead”.  🙂

ip as-path access-list

r6(config)#ip as-path access-list 71 permit _54$
r6(config)#router bgp 100
r6(config-router)#neigh 141.1.123.2 filter-list 71 out
r6(config-router)#do sh ip bgp neigh 141.1.123.2 adv | b Network
Network          Next Hop            Metric LocPrf Weight Path
*> 112.0.0.0        54.1.1.254               0             0 54 50 60 i
*> 113.0.0.0        54.1.1.254               0             0 54 50 60 i
*> 114.0.0.0        54.1.1.254               0             0 54 i
*> 115.0.0.0        54.1.1.254               0             0 54 i
*> 116.0.0.0        54.1.1.254               0             0 54 i
*> 117.0.0.0        54.1.1.254               0             0 54 i
*> 118.0.0.0        54.1.1.254               0             0 54 i
*> 119.0.0.0        54.1.1.254               0             0 54 i

I think that there is a typo in the output because there are routes from bb3 present, but we are not peering with bb3 in this lab:

bb3#sh ip bgp | b Network
 Network          Next Hop            Metric LocPrf Weight Path
*> 28.119.16.0/24   0.0.0.0                  0         32768 i
*> 28.119.17.0/24   0.0.0.0                  0         32768 i

11.2 BGP filtering – typo?

Or is it a typo?  According to this port bb3 should peer with bb1 and then pass the routes to r6? 

Task 11.2

I’m just going to ignore those routes.  I don’t have a peering between bb1 and bb3 in my lab.

11.3 BGP Connectivity

I hit the wall on this task.  I’ll have to come back and revisit it as I was so wiped from labbing that I just couldn’t handle mucking about with BGP redistribution.  😦

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2 Comments »

  1. I did this lab based on the initial bgp table i had below:

    Rack1R6#sib
    BGP table version is 14, local router ID is 150.1.6.6
    Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
    r RIB-failure, S Stale
    Origin codes: i – IGP, e – EGP, ? – incomplete

    Network Next Hop Metric LocPrf Weight Path
    *> 28.119.16.0/24 54.1.1.254 0 54 i
    *> 28.119.17.0/24 54.1.1.254 0 54 i
    *> 112.0.0.0 54.1.1.254 0 0 54 50 60 i
    *> 113.0.0.0 54.1.1.254 0 0 54 50 60 i
    *> 114.0.0.0 54.1.1.254 0 0 54 i
    *> 115.0.0.0 54.1.1.254 0 0 54 i
    *> 116.0.0.0 54.1.1.254 0 0 54 i
    *> 117.0.0.0 54.1.1.254 0 0 54 i
    *> 118.0.0.0 54.1.1.254 0 0 54 i
    *> 119.0.0.0 54.1.1.254 0 0 54 i
    *> 205.90.31.0 141.1.123.2 0 200 254 ?
    *> 220.20.3.0 141.1.123.2 0 200 254 ?
    *> 222.22.2.0 141.1.123.2 0 200 254 ?

    I created two as-path acls, one inbound route-map from R2 (blocking ^200_ )to get rid of:

    *> 205.90.31.0 141.1.123.2 0 200 254 ?
    *> 220.20.3.0 141.1.123.2 0 200 254 ?
    *> 222.22.2.0 141.1.123.2 0 200 254 ?

    And the an outbound route-map (blocking ^54_50_60 ) to get rid of:

    *> 112.0.0.0 54.1.1.254 0 0 54 50 60 i
    *> 113.0.0.0 54.1.1.254 0 0 54 50 60 i

    The outputs from both commands matched the requirements, but not the solution. The solution has no mention of the routes from as 200. I validated the solution answer has the same end result for the question. It never says using the least command. My question is, would this be considered wrong?

    Comment by Thomas — January 7, 2009 @ 10:37 pm | Reply

  2. Also while I am here (assuming anyone ever reads this).

    This question confused me at first until i figured out what they meant by ‘customers of AS 54’. Once I relized that just meant *anything* not originated by AS 54 it was easy. In fact, the solution for 11.3 seems much more complicated than it should be. Couldn’t you just do:

    –R6–
    ip as-path access-list 5 permit _54$
    !
    route-map BGP2RIP permit 10
    match as-path 5
    !
    router rip
    redistribute bgp 100 metric 1 route-map BGP2RIP

    Comment by Thomas — January 7, 2009 @ 11:49 pm | Reply


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