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  • Status: Solved
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new outside router ip

Hello I have a client that there isp is changing the outside ip address.
Here are the (old and the) new settings for the router and the mail server:
old IP address block: (subnet
new IP address block: (same)
old mail server address:
new mail server address: 2.2.2..22

how do I accompish they have a cisco 1600 router
1 Solution
Too many "it depends".. we'd need to see the existing config of that 1600 router. Is it doing NAT to the mail server? Does it have access-lists restricing inbound ports to specific addresses? Is the current config using "ip unnumbered Eth0" ?

>old IP address block: (subnet <== no way, jose. This mask is not correct

>new IP address block: (same) <== not with the above mask..

Basic router config:
router#config t
router(config)#interface serial 0
router(config-if)#ip address <new ip> <mask>

"new IP address block: (same)"

That should be

old IP address block: (subnet
new IP address block: (subnet


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