Origin Type
Motivation
In BGPs Best Path Selection Algorithm at step 3 the origin type of a prefix is evaluated. The following origin types exist (in descending order of preference):
- IGP - the prefix was generated statically with a BGP network statement
- EGP - the prefix was received via EGP (the predecessor protocol of BGP which no longer exists)
- Incomplete - the prefix was redistributed from another routing protcol (including static route) into BGP.
This rule has been overlooked for a long time, as the originator of a prefix sets this attribute and, according to RFC4271, it should not be changed by any AS forwarding the announcement.
However, it has been discovered that certain transit providers manipulate this attribute in order to attract more traffic. Keep in mind that this is evaluated after Local Preference and AS path length but before MED, so if a customer AS sets the same local preference to all its transit providers, a transit provider which modifies Origin Type from Incomplete to IGP attracts more traffic (if the AS paths have the same length).
Countermeasure
It is currently not possible to skip the evaluation of Origin Type in best path selection. So the only way to counter this behaviour of certain transit providers is to reset Origin Type for all received prefixes to the same value. This should only be done if you are a stub-AS and do not have any AS-customers.
Configuration
route-policy import-all
set origin igp
end-policy
route-map import-all permit 100
set origin IGP
/routing filter rule
add chain=import-all rule="set bgp-origin igp"
VyOS has two modes (operational and configuration mode). Enter configuration mode with
configure to make changes. Use commit to apply them and save to keep them after reboot.
set policy route-map import-all rule 100 action permit
set policy route-map import-all rule 100 set origin igp