Step 1: R1 and R3 IBGP Connectivity Using Loopback0
To establish IBGP between R1 and R3 using their Loopback0 interfaces and ensure updates originate from Loopback0, configure the following:
On R1:
router bgp 100
neighbor 10.3.3.3 remote-as 100
neighbor 10.3.3.3 update-source Loopback0
On R3:
router bgp 100
neighbor 10.1.1.1 remote-as 100
neighbor 10.1.1.1 update-source Loopback0
neighbor update-source Loopback0 ensures that the BGP updates are sourced from Loopback0.
Verify the BGP peering: show ip bgp summary
Step 2: R3 Can Ping R2 Loopback0 (10.2.2.2/32)
To allow R3 to reach R2's Loopback0, configure R1 to redistribute the route from EBGP to IBGP.
Ensure next-hop resolution works correctly:
On R1:
router bgp 100
neighbor 10.3.3.3 next-hop-self
next-hop-self: This changes the next-hop IP to R1's IP when advertising routes to R3. This ensures R3 can resolve the next-hop for R2's loopback.
Step 3: R1 Advertises Only Summary Route (172.16.100.0/22)
To advertise only the summary route 172.16.100.0/22 to both R2 and R3:
On R1:
router bgp 100
network 172.16.100.0 mask 255.255.252.0
aggregate-address 172.16.100.0 255.255.252.0 summary-only
aggregate-address 172.16.100.0 255.255.252.0 summary-only advertises the summary route and suppresses more specific routes.
Verification Commands:
Verify IBGP Peering: show ip bgp summary
Verify BGP Advertisements: show ip bgp
Verify R3 Reachability to R2's Loopback: ping 10.2.2.2 source Loopback0 Verify the Summary Route Advertisement on R2 and R3: show ip bgp IBGP Peering: Use Loopback0 and configure update-source.
Next-Hop Resolution: next-hop-self ensures reachability for EBGP routes.
Summary Route: Use aggregate-address with summary-only to advertise a summary route.