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BGP Route Anouncements... any ideas?

chrisbyrd

OSNN Junior Addict
#1
This isnt really specific to windows, but it seemed like the most appropriate forum

This might sound like an odd one...
Does anyone know how long it takes for BGP to reanounce routes to enough neighbour routers to get decent Internet connectivity restored?

For example:

Moving away from a single ISP to multihomed using BGP (not including original ISP). The IPs are all on private PI space. Completely new router with the same IP as the old one - so the old one needs to be turned off before the new one can be turned on (atleast on the same IP as the old one). Therefore, the neighbour routers of the old ISP will still be advertising that they can route the IP block... when they cant :(

What I'm basically asking is, does it take seconds, minutes or hours for BGP route information to be anounced?

Anyone got any ideas? :D
 
#2
well. We recentl had to shift 90% of our level3 routes to tiscallie and that took seconds after we stopped advertising them to level3, and seconds to mvoe back so I think thats your answer :D
 

Reg

eXperienced!
#3
The amount of time depends on your BGP configuration. The default settings are 60:180. Thus, at most it would take 180 for the propegation to take effect. However, most people run a 30:90, thus cutting the time in half that it would take to change.
 

chrisbyrd

OSNN Junior Addict
#4
LordOfLA said:
well. We recentl had to shift 90% of our level3 routes to tiscallie and that took seconds after we stopped advertising them to level3, and seconds to mvoe back so I think thats your answer :D
ah right. cool stuff

any particular reason why you moved away from level3? we're looking at using them as our main transit provider.
 
#6
chrisbyrd said:
any particular reason why you moved away from level3? we're looking at using them as our main transit provider.
our gateway router with them (meaning the router our fibre eventually ends up at after leaving our premsis) decided it wasnt going to route 90% of our traffic, so we just stopped advertising to level3 for the 15 minutes it took to get the issue resolved.

Since then Level3 has been fantastic and are still our prefered transit provider for reaching NYC in under 80ms.
 

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