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New Member

NAT configuration in Transition Mode

I have been tasked with moving a Backup server supporting in excess of 200 servers to a new network for expansion purposes.

The Server current address is

I have configured a Gigabit port on a 6506 IOS 12.1(8a)e with an IP address of as the IP NAT outside and connected this to the switch supporting the current network.

I have configured an Etherchannel Port-Channel 1 on the same 6506 with an IP address of directly connected to the Backup server which has an IP address of and set this as the IP NAT inside

I then configured an "IP NAT Source Static" statement.

When I execute a ping from the server to the I can see the source address being translated and I get a response. If I then send a Ping to an address in the network I get no response although I see the Source address being translated.

Examining the ARP Cache entry of the switch supporting the subnet I see the entry for the device as being "incomplete" I am expecting it to show the same MAC address as the address.

If I try and ping from a device in the network to the device I get no response and can see no translation being executed on the 6506.

The configuration is based on the Cisco "Configuring NAT Getting started" document Example using NAT during a network transition.


Re: NAT configuration in Transition Mode

Try doing traceroutes from the server to the devices that you were not getting a response from and from the devices to the server. Maybe there is a routing issue that is the cause of the problem.

New Member

Re: NAT configuration in Transition Mode

Thank you for you response. I have managed to fix it now.

The problem is because the Cisco IOS for Routers default is to enable IP Proxy-Arp but the IOS for MSFC/Switches defults to No IP Proxy-Arp. By enabling IP Local-Proxy-Arp on the interface that faces the original network the MSFC/Switch started to respond to messages for the NAT address.

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