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Issues with 32 bit mask on Wan link


I am trying to setup two 877 routers so that they talk to each other over GRE/IPSEC . However I need to be able to set my ATM0.1 (Dialer0) to static rather that assigned so that I can then setup the tunnel. However whenever I try to add the Public IP address in of 85.x.x.180 I get a bad mask /32 error.

After looking around I found an article that said set Dialer0 to unumbered and point to a Loopback address which is set to 85.x.x.180. I can do this but then Nat does not work. Could someone please help

Here is a copy of the config


Re: Issues with 32 bit mask on Wan link

did you got 85.x.x.180 public IP from ISP?

generally it should be /30 mask and not /32, you can ask your ISP as what is the subnet mask for this public IP.

you can also try to config subnet mask as instead of and see if it works for you.

hope to help ... rate if it does ...

Cisco Employee

Re: Issues with 32 bit mask on Wan link

Use the loopback interface instead of the dialer interface as follow:

ip nat inside source list 3 interface lo0 overload

It should solve the issue.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
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