BGP Route Advertisements

[dscarfe]

Hi, I have peering sessions with multiple ISPs.  I am currently advertising a public /16 to these peers, but I would like to gain more control on my inbound traffic by breaking my bgp advertisements into /24's.  My plan is to add 256 network statements to my bgp configuration.  I currently utilize a static /16 route to direct traffic back toward my firewall which enables the bgp route advertisement.  My preference is to use static routes to get the routes into my bgp router's routing table, but I would be happy to entertain other suggestions.

Is there any way to accomplish this without configuring 256 static routes?

Many thanks

Dave

[milan.kulik]

Hi,

I don't see any other easy way.

But is it really a good idea?

I remember from some other discussion, some ISPs were blocking/aggregating prefixes smaller then /19?

(In some older IOS version there was a limit of maximum 200 network statements, but it's gone already.)

BR,

Milan

[dscarfe]

Thanks for the reply Milan.

My ISPs have assured me that they will take up a /24 prefix with no downstream aggregation by them.  I think that what I was describing was an extreme scenario.  I'll probably start with something like a series of /19 and give myself the option of further splitting things up if I still can't balance things nicely. I would still like something a bit more elegant if possible....

Later,

Dave

[milan.kulik · Accepted solution]

Hi Dave,

the question is:

Wouldn't some other providers block /24 (somewhere  on other continent, e.g.)?

Regarding some more elegant solution:

You just need to get proper prefixes to your routing table. Then you can apply the BGP network command.

You could peer by some IGP (OSFP, e.g.)  with your FW.

But most people don't consider this safe.

BR,

Milan

[dscarfe]

Thanks Milan,  I see at least 71000 /24 routes in my bgp table, so not  accepting /24 upstream seems unlikely.  I can see where upstream providers may aggregate,  but I realize that I can't control that. If I do it, however, I'll keep that in mind if there are reachability issues reported.

Thanks for the suggestion of using an IGP...I'll have to take a closer look at that option....

Later,

Dave