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New Member

BGP, two ISPs, and a Class B

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!

1 ACCEPTED SOLUTION

Accepted Solutions

Re: BGP, two ISPs, and a Class B

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

6 REPLIES

Re: BGP, two ISPs, and a Class B

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).

Re: BGP, two ISPs, and a Class B

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

New Member

Re: BGP, two ISPs, and a Class B

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

Silver

Re: BGP, two ISPs, and a Class B

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.

Re: BGP, two ISPs, and a Class B

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

New Member

Re: BGP, two ISPs, and a Class B

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

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