1 WAN link on 2 Routers running HSRP

[Ashish Kumar]

Hey Folks,

Looking for help...

I have 2 ASR 1001X routers  for WAN connectivity for Data Center. In this scenario, ISP is giving a single WAN connection (x.x.x.x/30) with 2 physical links.

Now I have 2 physical connections but only 1 IP at my end. Internally I'm running HSRP at local LAN side.

Any idea how to connect both routers in redundancy with /30 subnet.

Regards, 

Ashish.

[Richard Burts]

You do not tell us what kind of WAN links these are. If they were serial links which could be configured to use PPP encapsulation then Multilink PPP would be an option which could achieve your objective. With MLPPP multiple serial interfaces operate as a bundle and have a single IP, so the /30 could work. If you do not have the option to use MLPPP then it would be difficult to implement two links to the ISP with a single /30.

Thinking way outside the box there is one alternative that occurs to me which might work. If you connect both ISP links in a switch and configure the two ports in a port channel, then you could assign one IP to your end of the port channel and the ISP would need to have a corresponding setup with the two links connected to a switch and configured as part of a port channel with the other IP. Then you could connect both of your ASR to the switch in a different vlan and do inter vlan routing on the switch.

Other than that I am not clear how you could utilize two ISP links with a single /30. Perhaps you can ask the ISP how they would suggest using two links with a single /30 subnet.

HTH

Rick  

[Ashish Kumar]

Thank You Rechard,

These two links are connected to Gig port of ASR routers, i don't have serial link.

The basic requirement of customer is to have router level redundancy if one ASR fails another to take over in host standby.

Regards,

Ashish.

[Richard Burts]

Asish

I find it puzzling that someone would negotiate with an ISP for two links and only a single /30 subnet. The traditional solutions for providing router redundancy would be:

- use 2 subnets (one for each router) and perform equal cost load sharing on two links to ISP. But that would require 2 subnets with /30.

- use HSRP for the router connections. But HSRP would require at least 4 usable addresses in the subnet (one for the virtual address, one each for the router physical addresses, and one for the ISP).

The only solution I can think of is the one I suggested in my previous post which uses port channel.

The optimum solution for providing router redundancy with no single point of failure is two ISP links, two subnets to connect to ISP, and equal cost load sharing.

HTH

Rick