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Community Member

HSRP possible with one public IP?

I have a site with a router that I would like to make redundant. My connection to the ISP is ethernet all the way, and I currently have only one public IP

address between my last hop and the ISP. Is it possible to use HSRP to make this router redundant on both eth0 and eth1 interfaces? I was successful in

setting up HSRP for the eth1 interfaces, but I have plenty of public IP's to use on the eth1 side. I attempted to create a standby ip for the eth0 interfaces using my eth0 IP address, but the router

complained that the IP was currently in use by eth0.

I also tried creating bogus IP addr's on eth0 with the legit IP for the standby IP, but that failed to route traffic to the ISP.

My goal is that if either link (eth0 or eth1) goes down on the active router, the standby router will then take over.

Note BGP is not an option as the ISP is unwilling to support.

Thanks

3 REPLIES
Community Member

Re: HSRP possible with one public IP?

This is a lame diagram that should help explain.

Bronze

Re: HSRP possible with one public IP?

HSRP won't work unless the standby ip is on the same subnet as the interface's real IP's. The reason is the routers use there real interface IP's and MAC's when forwarding traffic on the HSRP segment.

Daniel

Silver

Re: HSRP possible with one public IP?

Hi

I didn't read your files, so I'm using exampel adresses for this config.

I'm not sure if this config is working, but it's worth to try.

router_1

int eth0

ip address 192.168.1.2 ( faked address )

standby ip 192.168.1.1

standby ip 1.2.3.4 secondary ( real adress )

ip route 0.0.0.0 0.0.0.0 1.2.3.3 eth 0

ip route 1.2.3.0 eth 0

router_2

ip address 192.168.1.3 ( faked address )

standby ip 192.168.1.1

standby ip 1.2.3.4 secondary ( real adress )

ip route 0.0.0.0 0.0.0.0 1.2.3.3 eth 0

ip route 1.2.3.0 eth 0

regards

Mike

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