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totaramFlag for United States of America

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HSRP Between the two Routers

We have two WAN Routers that connect to ISP. We want to run HSRP between the two nodes, but have only /30 IP Addresses, how do we set the virtual IP address for HSRP? 


Thanks 

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Predrag Jovic
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By simple networking rules -  you can't, since minimum 6 IP addresses are required - 1 for ISP and 3 your routers (+ network address + broadcast address). /29 is minimum required for this.


However, if your routers allow change of broadcast address there might be a solution.


Example:

10.0.0.0/30 - Range assigned by ISP

10.0.0.0 - network address

10.0.0.1 - ISP router

10.0.0.2 - your router

10.0.0.3 - broadcast address

ip route 0.0.0.0/0 10.0.0.1


If you would configure on your end:

10.0.0.3/29 - broadcast address (to match broadcast address on ISP router)

10.0.0.4/29 - router 1

10.0.0.5/29 - router 2

10.0.0.2 - HSRP virtual IP address

ip route 0.0.0.0/0 10.0.0.1


it might work :)


But, you should also have in mind that ISP most likely will assign next free /30 to other company and that network range will not be reachable from your network routers (in the example above 10.0.0.4/30).

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ASKER

Can one use the private IP Range just for HSRP and public IP range (/30) for regular P2P?

HSRP virtual IP address has to be from the same IP address range as IP address public IP address range. So, no, except where you are using HSRP to trigger event based response.


With event based response you could configure to failover traffic from primary to secondary router if interface ISP connected interface on primary router is down, but it requires careful planning.

Example of a script that could be modified to your case:
https://community.cisco.com/t5/routing/how-to-failover-based-on-line-errors/td-p/3062023





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noci

you may want to consider using VRRP instead. Which may allow voting & presence be measured on a different address.
(using aliases on the same I/F if needed.)

I'm not following you.


If you've got two WAN links, then you've got two IP addresses (one for each link).  


And you want to run HSRP on the WAN side? 

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ASKER

Yes Don, on the WAN links

@pedrag: extending the addresses depend on the last bit of your current "network"  address if the /30  is odd (f.e. 10.0.0.124/30)...10.0.00000000.111111XX   then it extends downward and needs no adjustment of broadcast and the network below is added.).

Have you been given a public IP range other than the /30? If not, you can't do it.

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Don Johnston
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ASKER

Don;

The ISP has agreed to provide Active/Standby among their PEs , not sure if we can drop the idea of HSRP between the WAN Links? Is it is either / Or kind of situation?

Do you have two circuits with /30s assigned to them? If so, have you been given any BGP info from the ISP?

The ISP has agreed to provide Active/Standby among their PEs , not sure if we can drop the idea of HSRP between the WAN Links? Is it is either / Or kind of situation?


I think you would be better off just running a routing protocol with your ISP.