CCIE Pursuit Blog

January 27, 2008

Internetwork Expert Volume III: Lab 4 – Section 5

Exterior Gateway Routing – 6 Points

5.1 BGP Peerings

This was a pretty easy BGP peering task.  You need to set up a confederation, so you’ll need to be familiar with:

bgp confederation identifier

bgp confederation peers

I did mess up a little bit. I configured “neighbor 150.1.5.5 ebgp-multihop” on r4.

r4 (AS 100) <— r6 (no BGP) —> bb1 (AS 54)

It turns out that I don’t need this command because r6 is bridging, not routing.

neighbor ebgp-multihop

I also missed “neighbor 152.1.37.3 next-hop-self” on sw1, but I did eventually catch that error when I found that I was not installing the bb2 routes on r3:

Without “neighbor 152.1.37.3 next-hop-self” on sw1:

r3#sh ip route bgp
B    119.0.0.0/8 [200/0] via 152.1.125.5, 00:28:44
B    118.0.0.0/8 [200/0] via 152.1.125.5, 00:28:44
B    117.0.0.0/8 [200/0] via 152.1.125.5, 00:28:44
B    116.0.0.0/8 [200/0] via 152.1.125.5, 00:28:44
B    115.0.0.0/8 [200/0] via 152.1.125.5, 00:28:44
B    114.0.0.0/8 [200/0] via 152.1.125.5, 00:28:44
B    113.0.0.0/8 [200/0] via 152.1.125.5, 00:28:44
B    112.0.0.0/8 [200/0] via 152.1.125.5, 00:28:44

r3#sh ip bgp | i Network|192.10.1.254
   Network          Next Hop            Metric LocPrf Weight Path
*  205.90.31.0      192.10.1.254             0    100      0 (7000) 254 ?
220.20.3.0       192.10.1.254             0    100      0 (7000) 254 ?
*  222.22.2.0       192.10.1.254             0    100      0 (7000) 254 ?

r3#sh ip route 192.10.1.254
% Network not in table

With “neighbor 152.1.37.3 next-hop-self” on sw1:

r3#sh ip route bgp
B    119.0.0.0/8 [200/0] via 152.1.125.5, 00:30:15
B    118.0.0.0/8 [200/0] via 152.1.125.5, 00:30:15
B    222.22.2.0/24 [200/0] via 152.1.37.7, 00:00:15
B    117.0.0.0/8 [200/0] via 152.1.125.5, 00:30:15
B    220.20.3.0/24 [200/0] via 152.1.37.7, 00:00:15
B    116.0.0.0/8 [200/0] via 152.1.125.5, 00:30:15
B    115.0.0.0/8 [200/0] via 152.1.125.5, 00:30:15
B    114.0.0.0/8 [200/0] via 152.1.125.5, 00:30:15
B    113.0.0.0/8 [200/0] via 152.1.125.5, 00:30:15
B    112.0.0.0/8 [200/0] via 152.1.125.5, 00:30:15
B    205.90.31.0/24 [200/0] via 152.1.37.7, 00:00:15

r3#sh ip bgp | i Network|152.1.37.7
   Network          Next Hop            Metric LocPrf Weight Path
*> 205.90.31.0      152.1.37.7               0    100      0 (7000) 254 ?
*> 220.20.3.0       152.1.37.7               0    100      0 (7000) 254 ?
*> 222.22.2.0       152.1.37.7               0    100      0 (7000) 254 ?

r3#sh ip route 152.1.37.7
Routing entry for 152.1.37.0/24
  Known via “connected”, distance 0, metric 0 (connected, via interface)
  Routing Descriptor Blocks:
  * directly connected, via FastEthernet0/0
      Route metric is 0, traffic share count is 1

5.2 BGP Bestpath Selection

“Configure the network so that AS 100 routes through r1 to reach prefixes originated in AS 254.”
“Use MED to accomplish this.”

set metric (BGP, OSPF, RIP)

I had the right idea for this task, but I boned it up.  IE used an aggregate-address on sw1 to ensure reachability to all networks advertised by the backbone routers.  They have a short writeup to explain their method.

aggregate-address

I REALLY need to study BGP some more.

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