HELP: BGP configuration for 2 ISP's

[md_s_mannan]

Hi All,

I need help to configure the following case: I need to establish BGP neighbor's with two ISP's. Then have to advertise my network through those ISP's. But need to control my packets flow. ISP1 will be prioritized for all packets flow. If it goes down then ISP2 will takeover. Which BGP feature I should follow to implement.

Thanks  in advance.

[Richard Burts]

You have not provided much detail about your environment and so our responses must deal in generalities. To configure what you have described you would use these BGP features: EBGP session to each ISP, use of weight or local preference to prefer one ISP over the other (this will control your outbound traffic), and prepend in your advertisement to the secondary ISP (this will control your incoming traffic).

HTH

Rick

[md_s_mannan]

Thanks very much Rick. Here is a brief about my environment. Voice packets will be traversed through the ISPs. Both the ISPs are connected to the same AS. Actually both the ISPs are introduced to work as an Active/Standby. Let me know more about specific environment requirements. Thanks again. It would be better if I could have similar, very similar kind of case studies.

Expecting a positive response soon.

//

Mannan

[Richard Burts]

Mannan

I find some parts of your response confusing. You mention that voice packets will traverse through the ISPs. But you do not mention anything about any other type of traffic.

I also do not understand what you mean when you say that "Both the ISPs are connected to the same AS" or what you mean when you say that "both the ISPs are introduced to work as an Active/Standby".

HTH

Rick

[md_s_mannan]

Hi Rick,

There is only Voice traffic. The voice traffics will traverse to specific AS (private AS). Those AS's are connected to both the ISP's. My concern is to establish neighborship to both the ISP's in such a way that, if one goes down then other can take over the traffic. Moreover to priorities one ISP to the other, so that incoming and outgoing traffics can traverse through the same ISP. This will ensure QoS.

Thanks Again.

//

Mannan

[Tagir Temirgaliyev]

do you have your own AS and Provider Independent IP subnet /23-/24 ?

without it use ip sla

[md_s_mannan]

I do have my own AS and two /24 IP block. And my ISP side has provided me /30 peering IP block.

Thanks.

[Richard Burts]

Mannan

Thank you for the additional information. Based on this I believe that the suggestions that I made in my previous response would be what you are looking for. You should configure EBGP between your router(s) and the ISPs. If you have a single router running BGP then there is no need for IBGP. And if you are using two routers for BGP then you need to configure IBGP between your routers.

It would help if we knew what the ISPs will be advertising to you and in particular to know if both ISPs are advertising exactly the same things (it might be only a default route, it might be partial Internet routes, or it might be full Internet routes). To the extent that they are advertising the same things you want to configure so that one ISP is primary and the other is secondary. If you are using a single router for BGP then you could use either weight or local preference to make one ISP primary. If you are using two routers then you would need to use local preference to make one ISP primary. This would control the traffic sent from your network using the primary ISP and if there is a problem with that ISP then traffic will automatically switch to the secondary ISP.

You would need to advertise your address blocks to both ISPs. You could use prepending to make one ISP primary and the other ISP secondary. This will control traffic that is sent to you and if the primary ISP is active traffic will flow through this one and if there is a problem then traffic will automatically switch to the secondary ISP.

HTH

Rick

[md_s_mannan]

Hello Rick, thanks for your broad reply. It really helps alot. To clarify more:

1. I do have single router, So EBGP is enough.

2. ISP's will advertise the default route only.

3. Both ISP's are going to advertise the same. Therefore, one ISP is primary and the other is secondary. So here I can use either weight or local preference (as single router) to make one ISP primary.

4. I need to advertise my address blocks to both ISP's. Here, I've to use prepending to make one ISP primary and the other ISP secondary.

I hope this clarifies me alot. Thanks for your prompt response, and waiting to have same on the next reply.

Thanks very much Rick.

//

Mannan

[Richard Burts]

Mannan

Based on what we know of your environment your understanding seems to be correct.

- You will need EBGP with both ISP and there is no need for IBGP.

- To make one ISP as primary and the other as backup you could use either weight or local preference. This will help to control how you send traffic out and will send traffic through the primary as long as it is available and if the primary fails then traffic will automatically be sent through secondary (and traffic will switch back to primary when it becomes available).

- You do need to advertise your routes to both ISPs and prepending will indicate to them that traffic from outside to you should come through the primary as long as it is available.

HTH

Rick

[md_s_mannan]

Rick, Thanks very much. Thanks a lot. Let me study on the aforementioned features, and prepare a dummy script and simulation as well. I'll share it with you. I hope there is nothing wrong to share the script and simulation file here.

Thanks again.

//

Mannan

[Richard Burts]

Mannan

It should not be a problem to share the script and simulation here.

HTH

Rick