Configure 4331 ISR Interface with a /32 IP Address

[ralph.davis]

Hi All,

My company has shipped a Cisco 4331 ISR to one of our remote offices.  The ISR (with Security option) will interface to the remote office's ADSL modem and out to the Internet.  The modem is capable of passing-through the IP address handed out by the office's ISP.  My issue is the ISP gave this office 1 IP address, so I'm dealing with a /32 address.  If I try to configure one of the interfaces on the ISR as a WAN interface with a /32 address the ISR rejects it with an "invalid mask".  I'm unsure what to do at this point.  Can someone point me in the right direction on this?

[Richard Burts]

Is it really a /32 address? I can certainly understand why IOS would not accept configuration of a /32 on a LAN or WAN address which is supposed to connect to some other device on an Ethernet interface. I would think it would work to configure the interface with a valid subnet mask and let it communicate through the modem. Part of the trick will be determining what address the router should use as its default gateway. Once you determine the gateway address choose a subnet mask for your interface that puts the router address and the gateway address in the same subnet.

HTH

Rick