Networking Problem

Post by **gannon** » Wed Mar 16, 2005 6:58 pm

I've been having a networking problem, so I figured since I can't seem to figure it out I might aswell ask here. Anybody with knowledge in that area?

Nightmare · Post by **Nightmare** » Wed Mar 16, 2005 7:05 pm

Try expanding the question a little...

What kind of problems? What OS are you running?

peppers · Post by **peppers** » Wed Mar 16, 2005 7:20 pm

whats your problem? noone can help you if you dont tell them what the problem is
I have lerned a lot about it from meny networking headaces myself

edit: I read below I onley know about option 1 and to a lesser extent 3 sorry

Post by **gannon** » Wed Mar 16, 2005 7:45 pm

I wanted to know what people knew of networking before I threw the question out there. The problem is not OS related at all actually.
I have a network setup with 2 gateway routers. 1 gateway connects the network to the internet, and the other segments a subnetwork. Right now the subnetwork has no connectivity with the rest of the network. There are a few solutions to throw out there, but I don't have access to them all.
Option 1: Go into each computer and manually add the second gateway to the routing tables
Option 2: Set up IRDP on the subnetwork's gateway router and use a flaw in windows to add the 2nd gateway to the routing tables
Option 3: Go into the local DNS server and add the 2nd gateway to it's routing table

Options 1 & 3 aren't really a viable option to me at the moment, and I couldn't get option 2 working correctly.

Any help would be appreciated

HK-47 · Post by **HK-47** » Wed Mar 16, 2005 8:27 pm

But can the subnetwork get to the internet? Can it even see the gateway?
And are you sure its not a hardware problem? Ex. Broken cables, something of the sort?

Post by **gannon** » Wed Mar 16, 2005 8:36 pm

I did option 1 to one of the machines outside the subnetwork and I got connectivity, so it's not a hardware problem.

Post by **Black Six** » Wed Mar 16, 2005 8:45 pm

So is router 1 connected to the internet and a few computers and router 2 is connected to a few more computers and then uplinks to router 1? In that case wouldn't you have all the computers on 2 go to 2 as a gateway and then 1 treats 2 just like another computer and lets it out to the internet or the other comps? I'm sure my dad could help, he's in the network security industry, knows all about that kind of stuff, whereas I'm stuck with the odds and ends that rub off in conversation...

metal_mattt · Post by **metal_mattt** » Wed Mar 16, 2005 9:59 pm

black six's method sounds like it would work. i have some network simulation software i can use to see if it works

Post by **gannon** » Wed Mar 16, 2005 10:02 pm

b6: That's kinda right, but because the 2nd router is a gateway to the subnetwork each ip in the subnetwork gets shown.
Say in the first network I have IP 10.0.255.254, the subnetwork's gateway is 10.0.255.255, and an IP in the subnetwork is 192.168.255.254. When I try and ping from 192.168.255.254 to 10.0.255.254 through the gateway, 10.0.255.254 sees 192.168.255.254 as the IP to reply to, but it doesn't notice that 10.0.255.255 is a gateway and that the subnetwork 192.168.255.0 needs to be accessed through it.

It's just that the routing tables in the first network don't know how to route through the 2nd router as a gateway.
I could try some NAT and multihoming on the subnetwork's gateway, but that's a kinda complex process.

diggerdanh · Post by **diggerdanh** » Thu Mar 17, 2005 12:11 am

Gannon,

Something is fishy.

(You probably know all this, but I am logically thinking through this myself, so bear with me)

Routers used as gateways as you have described have 2 interfaces (2 IP addresses) - one for the external network and one for the internal network.

For example, your gateway 1 has an external IP address - a public IP address on the internet - and an internal IP address, probably 10.0.255.1. All the computers in the main network refer to 10.0.255.1 as their gateway, including gateway 2.

Gateway 2 also has 2 interfaces: its interface in the primary network: 10.0.255.255, and its interface on the subnet, probably 192.168.255.1. All the computers on the sub network should refer to 192.168.255.1 as their gateway (not the ip address of the gateway on the primary network).

So if you ping from 192.168.255.254 (a computer on sub network) to 10.0.255.254 (a computer on primary network), 10.0.255.254 should see the IP to reply to as 10.0.255.255 - the IP address of gateway 2, not the sub network IP address of the specific machine.

Check to make sure that you have gateway 2's sub network IP (probably 192.168.255.1) setup as the gateway for all machines on that subnet and not the IP address of gateway 1.

Also, I may be mistaken, but I thought that the final .255 address should not be used by a specific machine - it is the IP address for an "all call" for all IP addresses in the network. I vaguely remember something about that, but I could be mistaken. You might want to change the IP address on the primary network of gateway 2 to something other than 10.0.255.255.

Let us know what you find out.

Post by **gannon** » Thu Mar 17, 2005 6:09 am

The IPs I just gave were just examples, not the real ones

Anyways, when I route a packet through the 2nd gateway, the MAC address gets stripped from it, but not the original IP address. To strip the IP address I need to do some NAT, or I could try multihoming the ethernet port on the router so that it has multiple IPs.
My main goal though would be to allow each client on the network to recognise the 2nd gateway. Once I succesfully get IRDP running on the router the gateway will be recognised and everything will route fine.

MajorLag · Post by **MajorLag** » Thu Mar 17, 2005 4:31 pm

Wait a minute.... why isn't there just a static entry in the internet gateway router pointing to the subnetwork gatway for that subnet? Sure it sounds awkward, but it should work.

Post by **gannon** » Thu Mar 17, 2005 4:38 pm

Oh yeah, forgot to mention that I don't have access to the main router.
I'm gonna try and ask the networking teacher at my school next week (I'd ask the tech admins if they weren't total dumbbums (see? I can follow the language rules!!

)

MajorLag · Post by **MajorLag** » Thu Mar 17, 2005 5:46 pm

gannon wrote:Oh yeah, forgot to mention that I don't have access to the main router.

Well that makes it somewhat harder. I'll need more information, what kinds of routers are we talking about here? The main router doesn't happen to be running a routing protocol does it (I doubt it, that would make it too easy)?

Post by **gannon** » Thu Mar 17, 2005 6:13 pm

Cisco 2500 series routers

I could give you the running config dump of one of them though. If all else fails I guess I could try and work on the DNS server to get the gateway discovery working right