Redundant Link Internet Access

Unanswered Question
Apr 16th, 2007
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i have got 2 Routers & 2 ISP's. Router-A connected to ISP-A, Router-B connected to ISP-B, now my requirement is, i shouldn't find any down time when ISP-A/Router-A fails, still i should able to access internet via ISP-B/Rotuer-B, that too without changing the Gateway IP on the user's PC, what is the best way?

at present 50% users are connected via Router-A & rest 50% users are connected via Router-B for accessing internet, when ever Router-A failz i will b changing the gateway IP address to Router-B, whomsoever where connected earlier on Router-A.

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saurabh1969 Mon, 04/16/2007 - 19:26
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You need to setup BGP. YOu need to have atleast class "C" from one of the ISP. Please check with your ISP as you need to advertise your network to both of them.

Anand Narayana Mon, 04/16/2007 - 20:28
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Hi Saurabh,

class A ipaddress with "Class C" subnet. with this how i configure.

Danilo Dy Mon, 04/16/2007 - 19:34
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Do you have your own AS and Public IP Address?

Are these two routers are in the same location (i.e. building)?

Anand Narayana Mon, 04/16/2007 - 20:31
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Hi Medan,

Yeah v hav the public address from 2 different ISP's, ofcourse two routers are nearby.

saurabh1969 Tue, 04/17/2007 - 13:38
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Which routers are those? You should start talking to your ISP about BGP and get an ASN from ARIN as that is the first step towards setting up BGP.

wil_amaya Tue, 04/17/2007 - 19:54
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if you decide to go bgp, you can take your two individual routers and use HSRP. you will then end up with one virutal ip address. you can then assign that as your gateway. what you would do is use the addressing assigned to you from your class c. Oh, btw, you only need one class c, not one from each provider. due to shortage of ip addresses, they make you fill out a bunch of forms to get approval for a class c.

anyway, back to topic - here is an example:

your assigned class c address is /24

on your router inside interfaces, you would assign as follows (your outside interfaces would have /30 addressing assigned to you by your provider).

router 1 -

router 2 -

standby ip router address - ( this is your hsrp)

configuring HSRP is a different story but its a good way to add redundancy and be able to use a single gateway even if you're using two ISPs.

Anand Narayana Tue, 04/17/2007 - 20:22
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understood abt the HSRP i using it over here, bcoz that was my idea earlier b4 posting this, but 2 different ISp. but 1 thing i wanted to get clear, for Router-1 you have mentioned the IP address & Router-2 & standby as, is correct or instead of u typed by mistake as

wil_amaya Wed, 04/18/2007 - 05:18
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you're right, that was a typo, i meant


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