notes: BGP Process

- BGP is a path vector protocol.
- TCP port 179 is used for reliable transport.
- BGP has no periodic updates, it uses triggered updates:
     - Every 5 seconds for internal peers.
     - Every 30 seconds for external peers.
- Periodic keepalives used to verify TCP connectivity:
    -Default every 60 seconds.
- Holdtime interval: Time if passed with no received keepalive, before a notification message is sent, (default = 180 seconds).
- Only the holdtime is sent in updates. Two peers will agree on the lowest holdtime value between them, and then calculate the
keepalive value based on this holdtime value.

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COMMANDS
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1. - Enables BGP routing process

router bgp {as-number}

2. - Configures the RID for BGP Process, not used like the IGPs

bgp router-id {ip}

3. - Changes the default value of BGP scanner process runs (max/default = 60 sec)
- The BGP scanner walks the BGP table and confirms the reachability of next hops
- The BGP scanner process is also responsible for conditional advertisement check
and performing route dampening

bgp scan-time {scanner-interval}

4. - Changes the default values (60sec, 180sec) of BGP timers
- Only the holdtime value is communicated in the BGP open message
- Smallest configured holdtime value between BGP peers are used by both peers and
used to determine the keepalive

timers bgp {keepalive} {holdtime}

 5. - Changes the default time interval in the sending of BGP routing
updates for a specific neighbor
- If lowered, can improve convergence, but can consume considerable resources
in a jittery network if value is too low. (Range 0 to 600 seconds)
- Default values: 30 sec for eBGP neighbors, 5 sec for iBGP neighbors

neighbor {ip|peer-group} advertisement-interval {sec}

6.   - Changes the default values of BGP timers per specific neighbor or peer group
- Per neighbor timer overwrites the process timers

neighbor {ip|peer-group} timers {keepalive} {holdtime}