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New Member

help needed with multihomed NAT

I trying to configure Cisco's 1841 router acting as gateway with NAT.

I have two ISPs and each of them gives me one IP.

Now I need to configure inside web and DNS servers to be accessible from outside via both ISPs addresses.

I think it is possible to realise by using route-maps with static translations.

Can someone suggest me rigth direction on how exactly it can be done, or some document where I can find additional info?

Here is first string from "show version" command:

"Cisco IOS Software, 1841 Software (C1841-ADVSECURITYK9-M), Version 12.3(8)T7, RE"

VIP Purple

Re: help needed with multihomed NAT


you are right about the route-maps and static translations, have a look at the document below for a sample configuration:

NAT - Ability to Use Route Maps with Static Translations

Regarding the DNS, this document might be useful:

White Paper

Enabling Enterprise Multihoming

with Cisco IOS Network Address Translation (NAT)



New Member

Re: help needed with multihomed NAT

do you regard own multiple ip block without own your AS and BGPsetting?

New Member

Re: help needed with multihomed NAT

I don't sure that I understand you rigth

Yes, I didn't own any AS and have only two IP addresses - one from ISP1 and one from ISP2

And because of this I didn't run any routing protocol

New Member

Re: help needed with multihomed NAT

i guess outgoing traffic from your inside PC, would be probably right action with upper configuration in URL

but, incoming packet to your WEB server(f.e) would choose one direction and 1 IP address from ISP#1 or #2

because you'd get IP1 from ISP#1 is belong to ISP#1s AS, and theother too.

I have no idea 'bout multiple dns records and multiple web servers' diffrent network.

I heard some other vendor's machine works pretty good with like yours.

New Member

Re: help needed with multihomed NAT


if u could post ur router configuration so we start a work around based on it , thanx

New Member

Re: help needed with multihomed NAT

I would really like to take part in this as I have a similar situ. One 1841, two ISPs, AND two /27s. Plan is to program the outside interface on our PIX [which is pointing "out" to the 1841] with IPs from ISP A [a T1]. The primary default gateway on the 1841 points to ISP A. Now, if the T1 goes down, the "plan" is to xlate the STATIC PIX IP to an IP on the address block from ISP2, which is a DSL connection. Since the source address is on the ISP2 network, packets from the PIX going out that way should be OK for inside users ... Yes?

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