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Metalshark
Asked: 2015-08-24 14:43:02 +0800 CST

Cisco IP Redirection (static NAT?) for non existant IP Range

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We are moving office and our managed service provider has let us down badly. We have a Cisco 4500 stack with 5 VLANS configured of interest. These are:

interface Vlan200
 description FLOOR0 Gateway
 ip address 172.17.0.1 255.255.252.0
!
interface Vlan201
 description FLOOR1 Gateway
 ip address 172.17.4.1 255.255.252.0
!
interface Vlan202
 description FLOOR2 Gateway
 ip address 172.17.8.1 255.255.252.0
!
interface Vlan203
 description FLOOR3 Gateway
 ip address 172.17.12.1 255.255.252.0
!
interface Vlan204
 description FLOOR4 Gateway
 ip address 172.17.16.1 255.255.252.0

Our old network was 10.0.0.0/8 (inherited it). An example server would be 10.0.0.81. Our entire environment (several thousand devices) cannot be reconfigured to point at our new 172.17.4.81 address as the package deployment for SCCM has just collapsed.

The 10.0.0.0/8 range is not on the 4500's (as it was handled over our MPLS so the MPLS default gateway on the 4500's sent traffic to it anyway).

Is it possible to use static NAT or similar for requests to 10.0.0.81 to point to 172.17.4.81? I became nervy when all examples show applying inside/outside rules to interfaces (I don't have one for 10.0.0.81/8 but could always create a stub VLAN). Also didn't know the consequences of applying it to the VLAN interfaces above (in case I lost access to our production network).

Guessing that adding inside/outside NAT would be harmless but would like to know how you Cisco geniuses would tackle this.

UPDATE:

We've fixed SCCM but for future reference it would still be great to know the best way to handle this.

cisco

1 Answers

  1. Best Answer

    Translate a whole network range is possible by using static NAT (aka Net Static). Anyway the problem here is that old network is a /8, while the new can be 172.16.0.0/12 at most (you forgot to specify this).

    So, unless you want to specify the translation of each IP needed, a good idea could be to select a subnet of 10.0.0.0/8 with the same size of your new network.

    Because you're talking about 172.17.4.81, and because the config shows 172.17.4.0/22, these commands can be used to translate 10.0.0.0/22 to 172.17.4.0/22:

    int vlan201
 ip nat inside
int vlanX # Every other VLAN
 ip nat outside

ip nat inside source static network 172.17.4.0 10.0.0.0 255.255.252.0
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