IP Networking

Hi;

I have a UNIX box (SCO 5.0.2) with two (2) NIC cards. One card (NIC1) talks to a network 57.14.65.x/27. The other card NIC2) talks to users on 57.14.103.x and 57.14.105.x with subnet mask of 255.255.0.0. If I set NIC2 to this subnet mask (255.255.0.0) it seems like the NIC traffic is now going to this one so we changed the NIC2 subnet mask to 255.255.0.0 which now works with 57.14.103.x and 57.14.105.x but I loose the 57.14.65. If I change the subnet mask to 255.255.255.0, everything work but I loose communication with the users at 57.14.105.x.

NIC1: IP Address: 57.14.65.166 subnet mask: 255.255.255.224
NIC2: IP Address: 57.14.103.220 subnet mask: 255.255.0.0

We know that NIC1 settings work OK so we don't want to mess around NIC1. We replaced NIC2 and now the system is having this problem. Any suggestions are welcomed.

Thank you

The netmask is quite literally that, a mask.

If you configure with 255.255.0.0 and 255.255.255.224 as netmasks on the networks you mentioned, you are defining one as overlapping the other, so the system behaves as you have already seen, 255.255.0.0 means the every machine with an address starting with 57.14 is on this subnet, all 67840 of them.

You need to know the correct size for the netmask on that subnet, it's probably something like 255.255.252.0 that you're looking for, but you really need to find out from your networking people what size the subnet is.

Yes, reborg is right, there is no meaning of having a network ID of 57.14.103.x with a subnet mask of 255.255.0.0 since it'll match every thing after 57.14.x.x, here is proof for this:

Code:

Address:   57.14.103.0           00111001.00001110 .01100111.00000000
Netmask:   255.255.0.0 = 16      11111111.11111111 .00000000.00000000
Wildcard:  0.0.255.255           00000000.00000000 .11111111.11111111  
=>
Network:   57.14.0.0/16          00111001.00001110 .00000000.00000000
Broadcast: 57.14.255.255         00111001.00001110 .11111111.11111111
HostMin:   57.14.0.1             00111001.00001110 .00000000.00000001
HostMax:   57.14.255.254         00111001.00001110 .11111111.11111110
Hosts/Net: 65534

Since you are trying to connect two networks with one IP address, its not possible with a subnet mask of 24, you can go for a 20 bit subnet mask e.g. 57.17.96.x subnetmask 255.255.240.0 and here is the data:

Code:

Network:   57.14.96.0/20         00111001.00001110.0110 0000.00000000 
Broadcast: 57.14.111.255         00111001.00001110.0110 1111.11111111
HostMin:   57.14.96.1            00111001.00001110.0110 0000.00000001
HostMax:   57.14.111.254         00111001.00001110.0110 1111.11111110
Hosts/Net: 4094

It'll match 57.14.96-111.x like you are trying to match 57.14.103.x and 57.14.105.x, hope it helps.

Regards,
Tayyab