question on advertise IGP routes into an EGP?

[vodka1101]

How would you advertise IGP routes into an EGP: by redistributing routes from IGP to EGP or via static network statements? or some other ways. can someone please Explain it to me.

thanks

[pkhatri]

Hi,

The safest approach is to use network statements. When you do so, you know exactly what routes are going to be redistributed. However, that only works for static situations where you know the routes in advance. When you don't know the precise routes that you will be learning from your IGP, redistribution (with appropriate route-maps) is the approach to use.

So, in a nutshell, the choice depends on your situation.

Hope that helps - pls rate the post if it does.

Paresh

[mheusinger]

Hello,

just an additional remark to the post of Paresh. In case you talk about the internet, then you also need to take into account two requirements coming from the ISPs. First any announcement should be /24 or larger, because many large ISPs discard smaller networks anyhow. Second many ISPs use route flap dampening. This means if you withdraw-announce-withdraw-announce and so on, your networks will be dampened (i.e. not used and not announced) within many ASs. So you will have connectivity problems. This is the reason to use something like:

router bgp 65000

network 1.1.0.0 mask 255.255.0.0

ip route 1.1.0.0 255.255.0.0 Null0 250

which will provide the required stability in IP routing.

In case you use the EGP to f.e. an MPLS VPN you might want to announce any internal network - as fast as possible - because you use the EGP internally within your own VPN.

As Paresh wrote: it depends on your requirements - within your AS you can do what you want, when peering with another AS you have to take into account their rules as well.

Hope this helps! Please rate all posts.

Regards, Martin