Routing and Subnet Question?

Question

I support a small network that was already implemented. The DHCP assigns IPs for 192.168.11.x and 192.168.10.x (The default gateways are x.x.x.1 respectively.)

If I have a Cisco router that has one ethernet port configured as 192.168.11.1 and 192.168.10.1, would the two networks be able to talk to each other.

Its not like the router has a separate card configured with each IP. One card, two IPs. Can both be used as the gateway for the two networks.

Supposed someone on the 10 network needs to get to the 11 network. The packet gets sent to the router, but does the router know to send that packet back into the same port which it came to find the 11 network.

I always thought that differents networks should have thier own gateway and then create rules on the router to forward packets to the other networks.

Answer 1

Another posible solution is to use DOT1Q trunks if you also have a cisco switch and the router supports them.



Create two dot1q subinterfaces on the router and a trunk interface on the switch.



You then configure the switch for two VLANs placing the ports in each.



The advantage of this is you can now easily add more VLANS and subnets than just 2.



A good search string for this type of solution is "router on a stick"



This conf will also improve security as well and allow you to implement ACLs if you want



IN answer to the question above as well is the configuration will work fine

Answer 2

It is supported, either through secondary or through dot1Q trunking, but I would recommend the trunking option as another poster mentioned. The issue becomes DHCP, when you forward on the DHCP request, the primary address is always inserted into the packet, not the secondary, so the response usually comes back with an ip/dg accordingly. Using subinterfaces and trunking will fix that issue.



You can use smart-relay, but you need 12.4 IOS and I have heard little about it...



Hope this helps.

Answer 3

The router should work fine if it is configured properly. It should know from its routing table to send it back out the same port for the .11 network.



The two networks do have their own gateway (logical). They are just using the same physical interface.

Answer 4

Don't listen to them- it can be done very easily...



What you need to do is configure a secondary ip address on the router interface:



router(config-if)# ip address 192.168.10.1 255.255.255.0

router(config-if)# ip address 192.168.11.1 255.255.255.0 secondary



packets will route between the two subnets. each subnet will still have its own default gateway.

Answer 5

Only one IP per port. Your last comment is correct. If you are working with cisco routers, I recommend purchasing Cisco 1 and 2 books.