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connecting to two different ISPs

Unanswered Question
Apr 30th, 2006
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Right now I have one ISP link. In future we are getting another ISP link. At present our all servers are using present ISP public IPs.

My doubt is even though getting second ISP link, if first link goes down, how second ISP route the traffic to our servers which are using first ISP public ISPs.

So we are planning to implement BGP on internet router. Then how to implement BGP on it. We didn't own public AS number.



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vladrac-ccna Sun, 04/30/2006 - 10:22
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if you use BGP, you wont have any problems routing traffic to the second ISP, if the link to the first goes down.

And for the AS number, you dont actually need it.

You can you a private AS and you or the ISP can you use the following command:

neighbor {ip-address | peer-group-name} remove-private-as

to remove this private-as you are using, and you'll have no problems. (but this is not always necessary too).

How to implement BGP will depend on what you'll be doing? primary-backup ISPs? or load-share between the ISPs?

It not difficult to implement BGP on only 2 routers connected to the ISP, but will these routers be in different internal sites? are there other routers connecting these 2?

To give you a straight answer I'd need more information.


if it does, Id appreciate if you rate this post.


sivakondalarao Sun, 04/30/2006 - 23:38
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Hi Vlad,

We have only one router. It is connecting to two ISPs. Our servers are using public IPs provided by first ISP.



vladrac-ccna Tue, 05/02/2006 - 08:42
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So, the problem would be , how to reach those servers with IP on the 1st ISP if this ISP is down and your only connection out is using the 2nd ISP IPs?

Not sure if this will work, but could NAT be a solution?

then you'd be Natting iT only on the interface that goes to ISP2?


mounir.mohamed Sun, 04/30/2006 - 20:34
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Dear sivakondalarao,

First you need to get your (PI) address from your near {RIRs}, APNIC, AFRINIC, LACNIC,ARIN, BTW once you get your address range u will be able to run BGP with any whatever numbers of ISP's but regarding the ASN issue its RECOMENDED to own your ASN to be the orginator of your address but in the same time No problem to use private ASN as soon as your both providers agreed on that, I Belive its very early to talk about the configurations now because you have to talk to both ISPs first about which ASN gone be used if thay agreed on one private ASN it will be nice but if thay give you different AS numbers So you need to immplement AS translation anyhow i'm always recomend to my customer to use his public ASN to be full control about his address.

Please rate helpful posts

Best Regards,

Mounir Mohamed


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