Cisco Systems Routing between Primary and Seconday IP addresses

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Subject Author Date
Routing between Primary and Seconday IP addresses Paul 02-06-10
Posted by Paul on February 6, 2010, 7:45 pm
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I am using a Cisco 871 router. The internal interface is configured with a
primary IP address of 192.168.1.1 and a
secondary IP address of 10.0.0.1. I also have an Internet facing interface that
gets it's IP address from the ISP's DHCP
lease.

72.x.x.x.x represents the DHCP address on my external interface.

192.168.0.x represents the internal network or LAN.
10.0.0.0 represents a PAT forward to a firewall from the External interface.

I want to replicate behavior that a person would experience coming from the
Internet so I want to route packets between
the 2 IP's. Can this be done?

Posted by Martin Gallagher on February 6, 2010, 9:38 pm
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Paul wrote:

> I want to route packets between the 2 IP's. Can this be
> done?

It's the automatic default behaviour so it should "just work"(tm) unless
you've doen something to stop it.

--
Rgds,
Martin

Posted by JF Mezei on February 7, 2010, 2:55 am
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Paul wrote:
>
> I am using a Cisco 871 router. The internal interface is configured with a
primary IP address of 192.168.1.1 and a
> secondary IP address of 10.0.0.1. I also have an Internet facing interface
that gets it's IP address from the ISP's DHCP
> lease.
>
> 72.x.x.x.x represents the DHCP address on my external interface.
>
> 192.168.0.x represents the internal network or LAN.
> 10.0.0.0 represents a PAT forward to a firewall from the External interface.

What interfaces contain the 192.168 and 10.* IP addresses ? Some BVI
interface ?

I am not sure you want to "route" between the two. You may have to
replicate your IP NAT commands to have the last argument the 10.*
interface instead of the Dialer interface and add the apprpriate IP NAT
inside/outside commands to the interface definitions to "link" the two
subnets.

I haven't done this so not sure it will work.

To route beween two subnets in my case:

I have BVI 10 with 10.0.0.1/16
and Fast/Internet 4 with 10.1.0.1/16

I added "ip route 10.1.0.0 255.255.0.0 fa 4 permanent" to the config.
It appears to work, but have not tested all possible convolutions.

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