Troubleshooting BGP

 Most network engineers think troubleshooting BGP is complicated.

It's actually very simple.

There's a single Cisco command that can tell you what's wrong in 10 seconds or less:

👉 show ip bgp summary

This command shows the status of all the BGP neighbors on the device.

The only column you really need to care about is:

State/PfxRcd

If the neighborship has not been established, this field shows you the current status (Idle, Active, OpenSent, etc). (see link to my post about FSM states in the comments)

If the neighborship has been established, it shows you the number of prefixes received from that neighbor.

In short, it answers the questions:

Is the BGP session up?
If not, why not?
If it's up, am I actually receiving routes?

If you're not receiving the correct number of routes, you can troubleshoot further with:

show ip bgp neighbors [ip address] [advertised-routes | received-routes]

That's really all you need to know to troubleshoot most BGP issues.

But if you're curious, here's what the other columns tell you:
✅ V – BGP version (almost always 4)
✅ AS – Neighbor’s autonomous system
✅ MsgRcvd / MsgSent – BGP messages exchanged (helps spot stuck sessions)
✅ TblVer – BGP table version (should match between peers)
✅ InQ / OutQ – Queued messages (non-zero = potential problem)
✅ Up/Down – How long the session has been established (or down)

💬 Have you used this command before? How do you usually troubleshoot BGP?