C1111 dynamic and static IP on same interface

[train00wreck]

Hi, I have a C1111-4P device in front of a Comcast internet connection. Recently Comcast changed things and now if you want to access the diagnostic page of a standalone cable modem connected to your router, you have to NAT outgoing packets to be within a specific private IP subnet space (192.168.100.0/24, the modem takes .1 so your traffic needs to look like it is coming from .2 through .254). I have solved this on my Linux router by adding "192.168.100.2/24" as an additional IP on the WAN interface, then adding a NAT rule so that traffic from internal subnets is source NATted 192.168.100.2. Right now the interface config on the Cisco looks like:

interface GigabitEthernet0/0/0
 ip address dhcp
 ip nat outside
 zone-member security OUTSIDE
 negotiation auto
 ipv6 dhcp client request vendor
 ipv6 dhcp client pd hint ::/60
 ipv6 dhcp client pd PREFIX
 ipv6 address dhcp
 ipv6 address autoconfig default
 ipv6 enable
 ipv6 nd ra suppress

How do I add the 192.168.100.2/24 address to the interface? It seems like the CLI only allows "ip address" to be either a static address or "dhcp". In this scenario I need both here. Let me know any ideas, thanks.

[Flavio Miranda]

@train00wreck 

 This is not possible. Either you choose DHCP or the IP address as you already saw.

[train00wreck]

lmao are you serious??

[Flavio Miranda]

I am.

[MHM Cisco World]

You can add second IP as secondary but the only rule here primary (via dhcp) and secondary must not use same subnet 

MHM

[MHM Cisco World]

If you want to use IP in same subnet for NATing then simply use NAT pool' add IP to pool and use it in NAT

MHM

[train00wreck]

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@MHM Cisco World wrote:

If you want to use IP in same subnet for NATing then simply use NAT pool' add IP to pool and use it in NAT

MHM

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Well no, it will never be the same subnet. The DHCP address is the global one provided by Comcast, the cable modem subnet is 192.168.100.0/24. They should actually never be the same subnet...

[MHM Cisco World]

If you sure it not in same subnet you can use secondary IP.

MHM

[train00wreck]

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@MHM Cisco World wrote:

You can add second IP as secondary but the only rule here primary (via dhcp) and secondary must not use same subnet 

MHM

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um ok, that sounds kind of like what I want.... like the DHCP address will always be global and should be used for the outgoing NAT address for all traffic, EXCEPT traffic destined for 192.168.100.1. So I need to add 192.168.100.2/24 as a secondary IP? How would I do that? thanks

[MHM Cisco World]

As I mention secondary use only when primary and secondary subnet not same' since both IP in same subnet you can not use secondary.

Instead 

Here you can use 192.168.100.2 as static NAT 

Use 192.168.100.1 in Pool and use Pool for dynamic NAT

MHM