bgp neighbor relationship, bgp timers.

[sarahr202]

  Hi everybody.

R1--------------R2

Assume R1 and R2 are bgp neighbors. We power them on.

R1 sends open mesage to R1

R2 sends open message to R2

R1 compares Capabilities listed in received open message from R2 to its own, If they are a match, R1 moves to open confirmed state.

My question is what capabilities R1 is comparing? What capabilities must match on order for R1 to move to " open confirmed state" ?

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Timers in BGP

We have hello timers which is 60 second and holddown timer  which is180 sec.  Do they have to match  for neighbor relationship to form ?

How often updates are sent? Do bgp send flash update ?

thanks and have a great weekend.

[Nagendra Kumar Nainar · Accepted solution]

Hi,

By default when you configure BGP, IPv4 address family will be enabled. Assume you have IPv6 address family enabled on one side while not on otehr side, R1 will send capability that is not enabled on otehr side resulting in sending notification message and session will not come up.

We have hello timers which is 60 second and holddown timer  which is180  sec.  Do they have to match  for neighbor relationship to form ?

- Regarding the timers, you can have different timers on both side. Keepalive and holdtime will settle down to the lowest of both.

How often updates are sent? Do bgp send flash update ?

- BGP is incremental update based protocol. Also the BGP session is over TCP which is a reliable protocol. So there is no need for periodic update. It only send the update once and when it need to withdraw the prefix, it will send a BGP WITHDRAW message.

-Nagendra