Routing issue with dual ADSL Router !!!

Answered Question
Apr 25th, 2010

Hi Folks,

I got a situation with my router which is a 1760 with 2 ADSL Wics with 2 diferents ISP. What I want is any traffic that comes from internet to one of my interfaces, goes back for the same interface. I got a default route pointing to internet taking the first ISP with a lowest AD and other as backup, but what happen is when I try to reach the backup interface from internet It doesn't respond, but as soon as I put the backup link as primary the link is reachable again. The reason why I need both links on is because I got a web server behind the router and I want that users from internet can use both links to access it.

I´m wondering if I can solve this with vrf or pbr ?

Regards,

Francis

I have this problem too.
0 votes
Correct Answer by patrickvanham about 6 years 7 months ago

It would also work to set up 3 vrf's, one for isp1, one for isp2 and the third for the webserver. The two isp vrf's imports the rt for the webserver and the webserver imports the rt's for both isp vrf's. The same can be applied for internet access, an internet access vrf which imports both isp rt's and the isp vrf's import the internet access vrf.

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TYLER WEST Mon, 04/26/2010 - 03:58

Are you trying to use two different public addresses for the web server, one for each ISP?  VRF might provide you an option there.  You might be able to do something with PBR depending on how this is set up.

If you are just trying to use one address then I'm afraid you are out of luck.  You would have to advertise that address to the alternate ISP and I just don't think that's going to happen in the DSL world.

Tyler West, CCNP

CWI, Inc.

Francis Garcia Mon, 04/26/2010 - 05:14

Hi Tyler,

As you said I got two public address with 2 diferents isps. But what I cannot figure it out is how to make this set up to work with vrf. If u got a sample I'll be thankfull. I gotta tell u too that I have nat overloading with both ISPs for the local network and I'm just forwading port 80 to the web server from both interfaces.

Regards,

Francis

TYLER WEST Mon, 04/26/2010 - 05:24

I don't have a sample.  Just thinking on paper.  A VRF setup would require either two Ethernet on the private side or one Ethernet using 802.1q and subinterfaces.  One ADSL and one Ethernet (sub)interface would go in one VRF and the other ADSL and Ethernet (sub)interface would go in the other VRF.  The web server would need connections on two different networks or support 802.1q on one interface (which is becoming more common).

The trick would be to overload in the opposite direction toward the web server so that the web server knows which network to go back to.  Yes this would hide the client IPs which may not be desirable.  Modern Linux hosts using the advanced routing in the kernel can make a better determination of which interface to go back out of but that may not be your scenario.

Correct Answer
patrickvanham Mon, 04/26/2010 - 07:02

It would also work to set up 3 vrf's, one for isp1, one for isp2 and the third for the webserver. The two isp vrf's imports the rt for the webserver and the webserver imports the rt's for both isp vrf's. The same can be applied for internet access, an internet access vrf which imports both isp rt's and the isp vrf's import the internet access vrf.

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