BGP: Difference between revisions
Content added Content deleted
Line 568: | Line 568: | ||
= ASPath Prepend = |
= ASPath Prepend = |
||
Source: [https://www.noction.com/blog/as-path-and-as-path-prepending noction.com] |
|||
* AS path is a well-known mandatory attribute, which means that it’s present for all prefixes exchanged between BGP neighbors. |
|||
{{UC}} |
|||
* When a BGP router sends out an update to a neighbor in a different autonomous system (i.e., an external or eBGP neighbor), it adds its own AS number to the front (left side) of the AS path. |
|||
* So the AS path lists all the ASes that need to be traversed to reach the location where the prefix that the path is attached to is advertised from. |
|||
* As such, a traceroute should encounter those same ASes. |
|||
* The main purpose of the AS path is to avoid loops. |
|||
* Prepending means adding one or more AS numbers to the left side of the AS path. |
|||
* Normally this is done using one’s own AS number, using someone else’s AS number for this can have unintended side effects. |
|||
Config: |
|||
router bgp 65123 |
|||
neighbor 198.51.100.90 remote-as 65456 |
|||
neighbor 198.51.100.90 description IX peer |
|||
neighbor 198.51.100.90 route-map prepend out |
|||
! |
|||
route-map prepend permit 10 |
|||
set as-path prepend 65123 |
|||
= BGP Route Dampening = |
= BGP Route Dampening = |