Solved: BGP, two ISPs, and a Class B

aweise · ‎07-14-2009

Hello,

My organization has internet service through the same ISP, but with two separate physical circuits. We are doing BGP with them and having them route our Class B such that one portion is routed through circuit 1 and another is routed through circuit 2.

For example, 1.2.0.0/19 is announced to the ISP via circuit #1 and 1.2.224.0/19 is announced via circuit #2. They take care of announcing the entire 1.2.0.0/16 to the rest of the internet.

My question - can this same thing be done if circuit #2 was with a second ISP? Even though it is a Class B (of which we own the entire block), can two providers announce separate /19 subnets of it?

Thanks!

Mohamed Sobair · ‎07-16-2009

Hi Andrew,

you could definetely do that with two differnet ISPs, and control the traffic based on what you want.

As for /19, it shouldnt be a problem because some ISPs not all reuires minimum /24, Of course thier is always exceptional cases.

HTH

Mohamed

View solution in original post

Collin Clark · ‎07-14-2009

Typically the minimum size subnet a provider will announce is a /24 so a /19 shouldn't be a problem. You will have to work with both providers to make sure the advertisements work (you did state that your current provider summarizes your network).

Danilo Dy · ‎07-14-2009

Current practice is to allow minimum /24 network. It should be announce aggregated.

u1kumar2002 · ‎07-15-2009

yes, you can announce your both netork to both isp & fine tune the attributes as per your requirement for high availibilty of your networks.

Rest of the things will be taken care by the ISP's

Rick Morris · ‎07-16-2009

If you announce the routes out to two different providers via bgp then you MUST have your own ASN. This way the routes will be seen from your AS and not your providers. Since you will be multihomed in this set-up.

If your ISP is summarizing your traffic then you will need to make sure they stop that other wise you will never use one side. If you announce then the ISP should just forward your announcement upstream and you will be allowed to traffic shape and make adjustments however you want.

Mohamed Sobair · ‎07-16-2009

Hi Andrew,

you could definetely do that with two differnet ISPs, and control the traffic based on what you want.

As for /19, it shouldnt be a problem because some ISPs not all reuires minimum /24, Of course thier is always exceptional cases.

HTH

Mohamed

aweise · ‎07-22-2009

Thank you, everyone. This is the information I was looking for.