1.5.f Other BGP features

1.5.f i Multipath, add-path

BGP routers and route-reflectors propagate only their best path over their sessions. The advertisement of a prefix replaces the previous announcement of that prefix (known as an implicit withdraw). While this achieves better scaling, it comes at a cost of preventing path diversity. BGP additional path is a BGP extension that allows the advertisement of multiple paths for the same prefix without the new paths implicitly replacing any previous paths, thus promoting path diversity and a reduction in MED oscillations.

router bgp <AS> 
 address-family ipv4 
 bgp additional-paths send receive 
 bgp additional-paths select group-best all 
 neighbor <ip address> advertise additional-paths best <number> 

1.5.f ii Soft reconfiguration, Route Refresh

Soft reconfiguration stores everything received from a peer in a separate table before applying any policy.  Since this is stored on a per-neighbor basis, this isn’t very efficient. 

Route refresh allows you simply request a neighbors prefixes again.

clear ip bgp <ip address | *> <in | out | soft>