Information Technology Reference
In-Depth Information
Step 3: Create iBGP Mesh Sessions and Intraconfederation eBGP Sessions
Create a peer group called Internal for intramember AS peers, and assign R5, R6, and R7
to the peer group. Create additional peer sessions for intermember AS peers. Thus, R4 peers
with R1 and R2. Physical addresses are used as peer IDs in this chapter, but loopback
addresses can be used as well. During the changeover, R1, R2, R4, R5, R6, and R7 might
complain that the peer is in the wrong AS. Ignore these messages; they are expected during
this phase of the migration. Additionally, R3's iBGP session with R4 is down, as expected.
Example 8-28 shows the new BGP configurations on R4.
Example 8-28
BGP Configurations on R4
router bgp 65001
no synchronization
bgp router-id 192.168.100.4
bgp log-neighbor-changes
bgp confederation identifier 100
bgp confederation peers 100 65000
neighbor Internal peer-group
neighbor Internal remote-as 65001
neighbor Internal update-source Loopback0
neighbor 192.168.14.1 remote-as 100
neighbor 192.168.24.2 remote-as 100
neighbor 192.168.100.5 peer-group Internal
neighbor 192.168.100.6 peer-group Internal
neighbor 192.168.100.7 peer-group Internal
no auto-summary
Step 4: Update the Configurations on R1 and R2 to Peer with R4
Because R1 and R2 are already part of the confederation, the configuration modification is
to change the current iBGP peering with R4 to eBGP peering, as shown in Example 8-29.
Physical addresses are used for the peering addresses here.
You can use several methods to make R8 reachable in a different member AS inside
confederation 100:
•
Make the link between R1 and R8 part of the IGP if the entire confederation shares
the same IGP. This is the recommended approach.
•
Reset the next hop to R1 using a route map for external routes only, and leave the next
hop of internal and confederation eBGP routes unchanged. This is probably the most
flexible method.
•
Set
next-hop-self
on R1 for all iBGP and confederation eBGP sessions. You should
avoid this method when migrating a network to or from a confederation architecture,
because temporary loops might form between routers in the confederation. This case
study demonstrates the danger of using this method and ways to avoid loops.
