Nokia SR OS BGP Implementation and Troubleshooting
Nokia SR OS BGP Implementation and Troubleshooting
This domain tests whether you can configure SR OS BGP with MD-CLI or classic CLI and diagnose a session or route problem with the right command instead of guessing.
Where things live
BGP configuration hangs off configure router bgp within the router instance, with groups, neighbors, families and policy references; route policy lives under configure router policy-options. Key show commands: show router bgp summary (peer state, uptime, prefixes received), show router bgp neighbor <ip> (timers, capabilities, families, last error), show router bgp neighbor <ip> received-routes and advertised-routes (what policy actually did), show router bgp routes <prefix> detail (attribute-by-attribute view of the decision), and show router bgp routes <prefix> hunt (every source, including rejected).
Diagnostic sequence
- Is the session Established? If Active or Connect, the problem is below BGP: no route to the peer, wrong local-address, TTL too low without multihop, or a filter on TCP 179.
- Established but no routes: check the negotiated family, then the import policy. A default-action reject with no matching entry silently drops everything.
- Routes present but not best: read the detail output - usually an unreachable next hop or a lower LOCAL_PREF.
- Best but not installed: compare the BGP route-table preference against other protocols.
Worked example
A new iBGP neighbor is Established but receives zero prefixes while other clients of the same RR are fine. show router bgp neighbor 10.0.0.9 shows the IPv4 family negotiated; received-routes is empty. The RR's export policy has default-action reject and one entry matching community "clients", but the new neighbor's routes were never tagged on import, so nothing matches. Fixing the import policy to add the community restores advertisement.
Traps
Using show router bgp routes when you need hunt to see rejected paths; assuming an empty advertised-routes is a bug when export policy is doing its job; and clearing a session with clear router bgp neighbor as a first step, which resets uptime and destroys evidence.