Subnet to Subnet Routing on LAN using Cisco router 1

[rootn5th]

Hi,
I've been trawling the web for days and cannot get the answer I need. I wonder if anyone can help?

Problem:

I need to communicate between to subnets on my LAN. The ideal solution would be a layer 3 switch - too expensive. Another would be a Router On A Stick configuration- still too expensive due to purchase of switch *and* router.

I really want to be able to do this with one piece of Cisco hardware such as an 851 or 861. These have two ethernet ports and I *think* they might do the job using RIP or similar, but rather than blow £200 to find out that they don't, has anybody got any experience doing this sort of thing?

Many thanks!
Sam.

 

[silverhairb]

What are your subnets?

[the other] Bill

 

[Lemon13]

just get any old cisco with 2 fastethernet ports, or get a pc with 2 nics to do the routing

 

[rootn5th]

Thanks for replies!

Well, the specifics of the subnets are irrelevant, but let's say:

192.168.1.0/24
192.168.2.0/24

1 windows server on each subnet and I need to get clients to see certain apps on each server from each subnet. Apps aren't important as they're easy.

I need to implement this on about 25 sites so, as you can imagine, costs can soon build up.

As for the suggestion of an old cisco with two fast ports, that sounds good. However, a new router with two fast ethernet ports sounds better as warranty, etc comes into play. I believe the 851 and 861 have two ethernet ports but I just don't know if they can both be configured on LANs with seperate subnets.

It's funny, I've set up site-to-site VPNs between Cisco boxes, modem-dialup backup systems, etc, etc, which have been quite complex, but there isn't a great deal out there on doing this simple job. Maybe it can't be done the way I want and I'll have to invest in a layer 3 switch for each site? Ouch!

Cheers...

 

[burtsbees]

I am not sure about the 851, but if the ethernet ports are L3, you're set---one subnet on each. However, some of those 800 series routers will have only L2 ports (L3 logical), like the 837, and ome can do vlans with a few L3 SVI's in them (like the 871). You'll have to research this, or maybe someone who has an 851 can enlighten us. This should not be a problem.
The best way is to try and put an IP address on each of the two ethernet interfaces.

Burt

 

[silverhairb]

For those two addresses, just change your subnet mask to 255.255.240. That would let those addresses communicate across the same LAN.



[the other] Bill

 

[rootn5th]

Thanks again. Some interesting comments here.

I can see what Burtsbees is saying - the switch ports might be just layer 2 ports and I'll not be able to configure them as I wish. A bit of research found this article:

http://articles.techrepublic.com.com/5100-10878_11-6102399.html

Seems like the 871 might do the trick with VLANS. I'm sure Cisco say that the 851 and 861 have VLAN support but maybe not to the same extent. Thanks for the prompt here.

As for subnetting, perhaps Silverhairb might be on to something.

I could do with more than 14 hosts per subnet but I can see that applying a different subnet mask might just work. I could of course use a class b mask for more flexibility.

Question is, do I need a router for this or would I just need to change the settings on the DHCP on the Windows server? This might cause issues with printers and things but might be worth it...

 

[silverhairb]

I meant to say use a subnet mask of 255.255.240.0. That would give you over 4000 hosts on the same network. 255.255.224.0 might be better since there are 25 different sites (one subnet address range for each site).

My understanding is that you should change the mask on the DHCP server and any device that has a fixed IP address. That might mean hitting the printers if they have fixed addresses. Probably need to change the mask on the router.

[the other] Bill

 

[silverhairb]

I don't think the 851 fastethernet LAN ports are L3. I think they are just L2. The 871 LAN ports are L3.

[the other] Bill

 

[rootn5th]

Thanks, I think I realised that but did my maths wrong and confused myself. It's one of those "why didn't I think of that?" moments! Great idea and cheers for responding.

My only dilemma now is that the ADSL routers are managed by the ISP and we can't change the internal IP address. I think an 851 between LAN and ADSL router will be able to route between the two and I won't have to worry about VLANs or Layer 3 ports and the like.

Cheers,
Sam.

 

[burtsbees]

You can set a layer 3 SVI for a vlan in the 851, but I don't know how many.

Burt