bgp synchronization

[Tony JOrdan]

HI Everyone,

just a quick question concerning the bgp synchronization. Why was synchronisation ever created ? ie in view of the IGP having to know the route ( in a transit AS) for connectivity to be maintained (bgp being distributed into the IGP thus uable to support a full internet table)

thanks

tjskier 

[Richard Burts]

The reason that synchronization was originally a requirement was to prevent the possiblity of a black hole that could be created if BGP knew of some routes but those routes were not known in the IGP.

HTH

Rick

[Tony JOrdan]

Ok thanks Rick,

I can understand that too. What I seem confused with is why would any one design or have a transit AS with an IGP involved in the first place knowing the constraints of IGP's handling an internet route table to avoid blackholing?

Cheers

Tony

[Giuseppe Larosa]

Hello Tony.

BGP synchronization is an old concept and it is now disabled by default in modern IOS versions.

In modern SP networks there is no need to redistribute the BGP into the IGP, even if there are internal nodes not speaking BGP the key technology is MPLS.

The P nodes internal in MPLS clould do not route they switch MPLS PDUs without examining the inner payload.

Combining an IGP for instrastructure only (to advertise loopback addresses), MP BGP and MPLS (either LDP or RSVP-TE) the SP have built a really scalable signalling plane.

However, it is good to know what BGP synchronization is and this has been explained by Rick.

Hope to help

Giuseppe