BGP Lab 8 Configuring iBGP (CCNP Level)

Download Lab: GNS3

Image requirements:
 Cisco IOSv        (vios-adventerprisek9-m.vmdk.SPA.156-2.T)

This lab retains configurations from the previous lab, you need to configure iBGP within autonomous system 250, before enabling iBGP peers it is necessary to configure IGP to advertise the loopback IP address of AS250 internal routers.

Lab tasks:

1. Configure routing protocol OSPF with process id of 20 within AS250, use router's Loopback0 IP addresses as router-id for the OSPF process. Enable the OSPF process on the interfaces, do not advertise interfaces facing other autonomous systems. All routers belonging to AREA 0, make sure to advertise loopbacks.

2. Configure iBGP neighbors by using loopback0 interfaces, a full mesh logical topology has to form between all routers within AS250.

3. Verify that every router has iBGP neighborship to every other router in the AS250.

4. Routers R1 and R2 have to advertise their public subnets from network by means of redistribution of connected routes, using route-maps and ip prefix-list, configuration example will not contain this information use examples from previous labs.

5. Verify that routers ER1 and ER2 have learned about R1 and R2's public subnets.

6. Routers ER1 and ER2 have to advertise the summary route of to their eBGP peers. Use the aggregate-address command.

7. Verify that other ISPs are receiving the summary route of AS250. 

8. Save configurations on all affected routers.

Configuration example:
ER1(config)# router bgp 250
ER1(config-router)# no synchronization
ER1(config-router)# neighbor remote-as 250
ER1(config-router)# neighbor update-source lo0
Verify iBGP:
ER1# show ip bgp summary
ER1# show ip bgp neighbor

Change iBGP next-hop-address:
Because by default bgp router when passing down routes into iBGP cloud from eBGP peer will advertise routes with the next-hop address of its peer, other iBGP routers will have reachability issues, you can fix this problem by redistributing into iBGP network IP addresses of eBGP peers or you can use the neighbor next-hop-self command to change next-hop address.

In this topology, routers ER1 and ER2 will send routes from other autonomous systems to its iBGP neighbors with the next-hop addresses of routers ISP1 and ISP2, since routers C1, C2, R1, and R2 do not have routes in their ip routing tables to reach the next-hop address of upstream ISPs, these routes will not be flagged as best routes, meaning that there would be ip connectivity issue. Use the configuration below to fix this problem.

Configuration example:
ER1(config)# router bgp 250
ER1(config-router)# neighbor next-hop-self




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