troubleshooting Question

Cisco 5510 ASA route 2 subnets through same inside interface

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EvaUnit01Flag for United States of America asked on
RoutersHardware FirewallsSwitches / Hubs
13 Comments1 Solution984 ViewsLast Modified:
Hello fellow experts! I need some advice on a problem I have. My network is running out of IPs and after evaluating the different ways to create more IPs I decided to add a new subnet. We have a Cisco ASA 5510 and some 3com Layer 3 switches. We decided not to use Vlans to achieve routing between to the 2 subnets. We added a secondary IP to the 3com switch. We know we have to change the gateway of any device on the original subnet (is now currently the ASA) to the IP of the 3com switch in order to achieve proper internal routing between to the subnets. Here are the specifics of the network below.

Cisco ASA:
Inside interface:

3com 5500G:
2nd IP:

We have tested routing through the 3com by connecting a workstation to it and manually assigning it an IP of with as the gateway and another with with as its gateway. Traffic goes through fine.

The problem I have is on the Cisco side. It still routes the subnet fine with access to the internet and our other sites in different countries(site to site VPNs). The new subnet does not seem to have outside access. Since the 3com switch was able to route traffic to a laptop in the network it would also reason that it would route to the ASA(same subnet). Obviously all of these devices are connected to the 3com switch directly. So I must be missing something on the ASA.

I have added a dynamic NAT rule on the inside interface to allow traffic from the subnet to be translated to the outside interface. Just as there is one already on their for the subnet. I am currently working on my ccent/ccna so I am somewhat novice when it comes to this, can another expert point out what I am missing? Also I cannot ping the ASA from the laptop on the subnet.

Thanks, Marco.

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