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Cisco Router Commands

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I have a simple network, but can't find the answer. \
I want to conect 2 different private networks with 1 router in the middle (2621) The first network is a 10.0.0.0 and the second 192.168.0.0. I just want to PC's on one side to see the other side.

Is it more then IP routes?

9 replies

by joseph moore

Does your router have 2 Ethernet interfaces in it? If so, then this is actually very easy. Lets say you do a SH INT (or a SH IP INT BRIEF) and you see that you have an E0 and E1 ethernet interfaces.
Ok, that is good. Just configure E0 to be on the 10.0.0.0 network with a valid IP, and configure E1 to be on the 192.168.0.0/24 network with a valid IP. For example, say E0 can be 10.0.0.10 and E1 can be 192.168.0.10. Do this
ENABLE
CONF T
INTERFACE E0
IP ADDRESS 10.0.0.10 255.255.255.0
NO SHUT
EXIT
INTERFACE E1
IP ADDRESS 192.168.0.10 255.255.255.0
NO SHUT
ctrl+Z

Ok, do a SH IP INT BRIEF and it should list both interfaces with the new IP addresses you assigned them.

Ok, now plug the E0 interface into the switch/hub that you use for your 10.0.0.0 network, and the E1 interface into the switch/hub that you use for your 192.168.0.0 network (or VLANs or however you are segmenting the 2 networks).

by joseph moore

Ok, now do a SH IP ROUTE and it should look similar to the following:

router#sh ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 -OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route

Gateway of last resort is not set

10.0.0.0/24 is subnetted, 1 subnets
C 10.0.0.0 is directly connected, Ethernet0
C 192.168.0.0/24 is directly connected, Ethernet1

See how I have 2 C routes defined? Those are directly connect routes that the router know of. YOu see, for each network a router has a leg on, it then has a preferred route to that network. The administrative cost to that route is 1, the best you can get (unless you change it). So now, this router can route to either 10.0.0.0 or 192.168.0.0.

Now as for your client workstations, here are your options as I can see them:
1) set up a static route on whatever device you are using asthe "default gateway" for the 10.0.0.0 network, pointing the 192.168.0.0 network to the E0 interface on your router. Then on whatever device is the "default gateway" for your 192.168.0.0 machines, set up a static route on that device pointing the 10.0.0.0 network to the E1 interface of your router.

by joseph moore

or 2) you could set up static routes on all of your clients (every workstation and server) on the 10.0.0.0 network pointing the 192.168.0.0 network to the E0 interface of your router. Then set up static routes on each device on the 192.168.0.0 network, pointing the 10.0.0.0 network to the E1 interface of your router.

As you can see, it is easier to do option 1. Just add a route to your default gateways, pointing the other network to the appropriate interface of the router. You see, your clients on 10.0.0.0 will want to forward the 192.168.0.0 requests to the 10.0.0.0 default gateway anyway (since it is the gateway to other networks!). So, why not set up the routes on the gateways!

Now, this is just a simple 2 network routing issue.Imagine when you have dozens of networks!!!

by joseph moore

One last thing. With the router on each network leg, that removes the need of running any routing protocols on the router. YOu won't need them. So, if someone is telling you that you need RIP or IGRP or OSPF or something else, tell them that it is not necessary....
unless your router has only a single Ethernet interface. If so, then things get real interesting!

hope this all helps. Routing is very complex and exact.

by courtney

sorry I dont know how to respond to you. This did help.

great, thanks for your help. The part about the clients helped the most. I belive I have the router setup fine. It is the same way you did it. On the 10.0.0.0 side I have a PIX 501as the default gateway, so would I put a static staement on there pointing to the 192.168.0.0 networ? How would that look?

As far as the 192.16.0.0 network, it s default gateway is the router. Would I then add a static starem to the router? How would that look?

by courtney

great, thanks for your help. The part about the clients helped the most. I belive I have the router setup fine. It is the same way you did it. On the 10.0.0.0 side I have a PIX 501 as the default gateway, so would I put a static staement on there pointing to the 192.168.0.0 networ? How would that look?

As far as the 192.16.0.0 network, it s default gateway is the router. Would I then add a static starem to the router? How would that look?

by joseph moore

Ok so I understand your network better now. So, you do have the router set up correctly on the 10.0.0.0 network and 192.168.0.0 network. Good. Now, here is why you can't route between them.

>On the 10.0.0.0 side I have a PIX 501 as the default gateway

Yes, you need to put a route in on the Cisco PIX that points all 192.168.0.0 traffic to the 10.0.0.0 network IP address of your router. YOu do that, and that will be it! You will then be able to route between the two networks.
The reason the routing is not working now is that routing is really a 2-way street: you need a route to a remote network AND that remote network needs a route to you! So, your 192.168.0.0 machines can actually hit your 10.0.0.0 machines through the router, but the packets FROM the 10.0.0.0 don't know where to go. They hit the PIX, which does not know where to route them, and they are dropped there.
There should be something in the logs of the PIX relating to this.

Unfortunately, I have never touched a Cisco PIX, so I don't know how to set up a static route on it. I suggest this: post a new question stating you need to put a static route on a PIX and you don't know how. Copy the URL of this question and post it in the new question as a point of reference. Someone else here at TR will be able to tell you how to put that route on the PIX.

Once you do that, routing should be working and all will be well with your network.

Good luck.

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