I just ran across some timers and realized I need to sort things out for myself to be able to repeat before the lab exam.
What timers do we need to know with BGP and what do they do?
- BGP Scanner
- BGP I/O
- BGO keepalive/holdtime interval
BGP scanner is a function that runs per BGP process. It runs through all prefixes in the BGP table and checks the NEXT_HOP reachability for each prefix to verify that its still valid. It also runs conditional advertisement, route-injection and route-dampening. It imports new routes into the BGP table from RIB via network statement and redistribute commands.
I/O handles BGP Update and keepalive messages and is configured per neighbor. Since it tells the router how often it should update its neighbor with BGP update messages, this implicitly configures prefix batching. With a higher update timer, potentially more prefixes would be sent in same update. With an update-timer of 0, each prefix update would be sent with individual update messages and would not be batched at all.
Update/keepalive is configured per neighbor with the command “advertisement interval”
Configures keepalive advertisement and holdtime for the entire BGP process which is used to verify if a BGP session is alive or dead. Default values are 60 and 180 seconds.