BGP Verification
February 15, 2025 - Reading time: 3 minutes
In the previous lesson, we established iBGP peering between two routers in the same Autonomous System (AS 2350) and configured network advertisements.
Last Lesson's Summary:
- iBGP Peering Setup – We configured two routers (Router0 & Router1) to form an iBGP relationship.
- Network Advertisements – Router0 advertised 50.50.50.0/24 and 70.70.0.0/16 into BGP.
- Reachability Requirements – iBGP neighbors must be IP reachable before a BGP session can establish.
- Synchronization & Auto-Summary – The configuration assumes that synchronization is disabled and auto-summary is off to ensure proper route advertisement.
We ended the lesson with a challenge to verify iBGP was properly advertising routes and to advertise Loopback1 on both devices.
Verification Commands
Now that our iBGP session is established, we need to verify the following:
- Check if the BGP session is up
- Confirm advertised and received routes
- Check if the routes are installed in the routing table
1 Check BGP Peering Status
The first step is to verify that the iBGP session is established between Router0 and Router1.
Command:
Expected Output (If Peering Is Up):
Router0#sh ip bgp sum BGP router identifier 70.70.70.1, local AS number 2350 Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 192.168.86.40 4 2350 26 22 3 0 0 00:14:07 0
Key Points to Check:
- Neighbor IP (192.168.86.40) → Matches the configured neighbor.
- AS Number (2350) → Both routers must be in the same AS.
- State = Up → If it shows Active or Idle, the session is NOT established.
- PfxRcd (0) → Number of routes received from the neighbor.
If the peering is in the Active or Idle state, check and use troubleshooting steps below.
2 Verify Advertised and Received Routes
Once the BGP session is up, confirm that routes are being received correctly.
Command to Check Received Routes:
show ip bgp
Expected Output on Router1:
Router1#show ipbgpBGP table version is 3, local router ID is 2.2.2.2 Status codes: s suppressed, d damped, h history, * valid, > best,
i - internal, r RIB-failure, S Stale, m multipath,
b backup-path, x best-external, f RT-Filter Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path *>i50.50.50.0/24 192.168.86.45 0 100 0 i *>i70.70.0.0/16 192.168.86.45 0 100 0 i
What to Check:
- *> → Valid and best route is marked with *>.
- Next Hop (192.168.86.45) → Must point to the neighbor.
- "i" at the end → Indicates the route originated from iBGP.
If routes are not appearing, check the network statement and ensure the routes exist in the routing table (show ip route).
3 Verify If BGP Routes Are Installed in the Routing Table
Even if BGP receives routes, they must be installed in the routing table to be used for forwarding.
Command to Check Routing Table:
show ip route
Expected Output:
If the BGP routes do not appear in show ip route, check:
- Administrative Distance (AD) of BGP (200) – If a more preferred route (lower AD) exists, BGP won't install the route.
- Next-Hop Reachability – If the next-hop is unreachable, the route won't be installed.
Key Troubleshooting Steps
If the BGP session is up but routes are not being learned, check:
- Reset BGP connections
clear ip bgp *
🔍 PocketCLI will reset BGP establishments if needed.
- Neighbor Reachability
ping 192.168.86.40
🔍 If ping fails, check interface status with:
show ip interface brief
- BGP Neighbor Status
show ip bgp summary
🔍 If the session is in Active or Idle, check neighbor configuration. Also try to reset BGP connections.
- Next-Hop Reachability
show ip route
🔍 If the next-hop is not reachable, the route will not be installed.