BGP Table Status Codes

Verifying BGP

One of the best commands to verify and troubleshoot your BGP configuration is show ip bgp to see the BGP topology database. This is such an important command that it's worth looking at in depth. The command output lists a table of all the networks BGP knows about, the next hop for each network, some of the attributes for each route, and the AS path for each route. The sample output from this command was taken from an actual Internet BGP peer.

route-server>show ip bgp
BGP table version is 22285573, local router ID is 12.0.1.28
Status codes: s suppressed, d damped, h history, * valid, > best, i
 - internal,
       r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete

  Network     Next Hop         Metric LocPrf Weight Path
* 3.0.0.0     12.123.137.124                  0     7018 2914 9304
 80 i
*>            12.123.1.236                    0     7018 2914 9304
 80 i
* 3.51.92.0/23 12.123.137.124                 0     7018 ?
*             12.122.125.4     2366           0     7018 ?
*>            12.123.1.236                    0     7018 ?
* 8.6.6.0/24  12.123.137.124                  0     7018 701 14744
 14744 14276 i
*             12.123.145.124                  0     7018 701 14744
 14744 14276 i
*>            12.123.1.236                    0     7018 701 14744
 14744 14276 i
        

Networks are listed in numerical order, smallest to largest. The first three columns list each route's status. An asterisk (*) in the first column means that the route has a valid next hop. Some other options for the first column include the following:

Key BGP Table Status Codes

1. Best Path:

• The asterisk (*) indicates a valid route.
• The greater than symbol (>) denotes the best path among multiple available paths.
• This path is chosen based on BGP's path selection algorithm and is used for routing traffic.

2. d - Dampened:

• Routes marked with 'd' are dampened, meaning they are temporarily suppressed due to route flapping (frequent changes in route availability).
• This prevents instability and excessive updates in the network.

3. s - Suppressed:

• The 's' indicates that the route is suppressed, usually because the route is part of a summary route.
• Only the summarized route is advertised to peers, reducing the size of the routing table.

4. h - History:

• Routes with 'h' are in history state, indicating that the route was once available but is not currently reachable

5. r - RIB-Failure:

• The 'r' denotes a route that failed to install in the Routing Information Base (RIB).
• This failure could be due to a variety of reasons, such as administrative restrictions or other higher-priority routes.

6. S - Stale:

• 'S' marks a stale route, typically used in Graceful Restart scenarios.
• It indicates routes that are kept temporarily while BGP sessions are reestablished to ensure minimal disruption.
• Used with nonstop forwarding to indicate that the route is stale and needs to be refreshed when the peer is re-established.

Practical Application

Understanding these codes helps network administrators in multiple ways:

• Troubleshooting: Quickly identify and resolve issues related to route availability and path selection.
• Optimization: Ensure the best possible paths are used for efficient data routing.
• Stability: Maintain network stability by understanding the impact of route flapping and suppression.

Conclusion

BGP table status codes are an indispensable tool for network administrators, providing critical insights into the state of routes. Mastering these codes allows for effective troubleshooting, optimization, and maintenance of a stable and efficient network infrastructure.

Sources

https://notes.networklessons.com/bgp-table-status-codes

https://www.ciscopress.com/articles/article.asp?p=1565538&seqNum=7