Lab Objective
Establish an eBGP session between two routers in separate autonomous systems, advertise a local network from each router into BGP, and verify each router learns the other's advertised network.
Lab Purpose
eBGP is the protocol connecting separate organizations, and even a CCNA-level engineer benefits from understanding basic eBGP peering, since many enterprise networks maintain at least one eBGP session toward an ISP. This lab builds the foundational skill of establishing a session and confirming routes are actually exchanged.
Lab Topology
R1 (AS 65010) ---- Serial0/0/0 ---- Serial0/0/0 ---- R2 (AS 65020)
R1: 172.30.1.1/30, Loopback0: 192.168.100.0/24
R2: 172.30.1.2/30, Loopback0: 192.168.200.0/24Task 1: Configure Basic Interface Addressing
Configure the serial link addresses and a loopback interface on each router representing that router's local network to be advertised.
Task 2: Configure BGP and the eBGP Neighbor
Enable BGP on each router with its assigned AS number, and configure a neighbor relationship pointing to the other router's serial address and remote AS number.
Task 3: Advertise Each Router's Local Network
Use the network command within BGP configuration mode to advertise each router's loopback network.
Task 4: Verify the BGP Neighbor Relationship
Confirm the neighbor state reaches Established.
Task 5: Verify Route Exchange
Confirm each router's IP routing table contains the other router's advertised network, learned via BGP.
Solution and Verification
R1(config)# interface serial0/0/0
R1(config-if)# ip address 172.30.1.1 255.255.255.252
R1(config-if)# no shutdown
R1(config-if)# exit
R1(config)# interface loopback0
R1(config-if)# ip address 192.168.100.1 255.255.255.0
R1(config-if)# exit
R1(config)# router bgp 65010
R1(config-router)# neighbor 172.30.1.2 remote-as 65020
R1(config-router)# network 192.168.100.0 mask 255.255.255.0R2(config)# interface serial0/0/0
R2(config-if)# ip address 172.30.1.2 255.255.255.252
R2(config-if)# no shutdown
R2(config-if)# exit
R2(config)# interface loopback0
R2(config-if)# ip address 192.168.200.1 255.255.255.0
R2(config-if)# exit
R2(config)# router bgp 65020
R2(config-router)# neighbor 172.30.1.1 remote-as 65010
R2(config-router)# network 192.168.200.0 mask 255.255.255.0R1# show ip bgp summary
Neighbor V AS MsgRcvd MsgSent State
172.30.1.2 4 65020 8 9 EstablishedR1# show ip route bgp
B 192.168.200.0/24 [20/0] via 172.30.1.2
R2# show ip route bgp
B 192.168.100.0/24 [20/0] via 172.30.1.1Key Takeaway
Unlike an IGP's network command, which simply enables the protocol on matching interfaces, BGP's network command specifically advertises that exact prefix into BGP only if a matching entry already exists in the local routing table — an easy detail to overlook when a network is not actually being advertised as expected.