squirrelworks
Border Gateway Protocol (BGP) is the fundamental "language" of the internet, functioning as a Path Vector protocol that manages how packets are routed across the globe. This lab focuses on establishing external eBGP adjacency between AS 100 (Core) and AS 200 (ISP), verifying prefix propagation, and hardening the interface against unauthorized traffic using Extended Access Control Lists. Mastering BGP is essential for ensuring redundant, stable connections in enterprise and campus environments where traffic must traverse multiple external providers.
! Define Core interface and establish neighbor relationship
Router0(config)# int g0/0
Router0(config-if)# ip addr 192.168.1.1 255.255.255.252
Router0(config-if)# no shut
Router0(config-if)# router bgp 100
Router0(config-router)# neighbor 192.168.1.2 remote-as 200
Router0(config-router)# network 10.10.10.0 mask 255.255.255.0
! Establish neighbor relationship and verify prefix receipt
Router1(config)# int g0/0
Router1(config-if)# ip addr 192.168.1.2 255.255.255.252
Router1(config-if)# no shut
Router1(config-if)# router bgp 200
Router1(config-router)# neighbor 192.168.1.1 remote-as 100
Router1# show ip route bgp
! Define Extended ACL: Deny ICMP, permit BGP (TCP 179) and other IP traffic
Router0(config)# access-list 101 deny icmp any any
Router0(config)# access-list 101 permit tcp any any eq 179
Router0(config)# access-list 101 permit ip any any
Router0(config)# int g0/0
Router0(config-if)# ip access-group 101 in
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.1, timeout is 2 seconds:
UUUUU
Success rate is 0 percent (0/5)
The lab is successful. We have established eBGP adjacency while simultaneously securing the interface. The "UUUUU" (Unreachable) status on Router1 verifies that ICMP packets are dropped, confirming that the Extended Access Control List is correctly blocking management-plane traffic while the control-plane (BGP/TCP 179) remains active.