This is a subnetting problem. NT Server will NOT forward packets to addresses
which are supposed to be in the same block. The block is determined by the
Subnet mask. Take a look at the following table:
Subnet mask: Block size (usable) Blocks in a
Class C address
255.255.255.0 256 addresses 1 block
255.255.255.128 128 addresses each 2 blocks (0-127,
255.255.255.192 64 each 4 blocks
Note: Each Block is delimited by two unusable addresses (first and last), so
a .192 mask actually defines 62 USABLE addresses.
Now that we've covered that, keep in mind what we stated earlier, which is that
NT does not forward packets within the same block. IF both NIC's are part of
the same block, NT assumes that there is some direct cabling scheme somehow
connecting both NIC's and that the two sides will eventually get the message.
(you would want it to assume this if you DO in fact have two NIC's on the same
side for performance reasons, since it will cut down on your network chatter).
Trick here is to cut you assigned block into pieces, and put the NT server
between the two pieces. For example:
IP address Subnet Mask
NIC1 (internal) a.b.c.1 255.255.255.128
NIC2 (external) a.b.c.129 255.255.255.128
if you refer to above, the two NIC's are not part of the same block, so routing
and packet forwarding will occur.
Problem here is to "keep" as many IP addresses on the Internal side as you can,
and keep the outside small. Ideally, you could request a single IP address for
NIC2 from your ISP. Just make the address something outside of your block, and
life is grand. Otherwise, try this example:
NIC1 a.b.c.1 255.255.255.128
NIC2 a.b.c.252 255.255.255.248
You would then have to add some additional routes to your routing table, all of
them pointing to a.b.c.1. In this example:
ROUTE ADD A.B.C.128 255.255.255.192 A.B.C.1 ("recovers" 62
ROUTE ADD A.B.C.192 255.255.255.224 A.B.C.1 ("recovers" 30
ROUTE ADD A.B.C.224 255.255.255.240 A.B.C.1 ("recovers" 14
ROUTE ADD A.B.C.240 255.255.255.248 A.B.C.1 ("recovers" 6
It's a royal pain to set up, but it does work and it is quite stable once you
Hope this helps.
> I have an internal network with C Class Ip address, and a router (Cisco
> 2500) as gateway to the Internet.
> I want to set up an NT server (Alpha-based) with two NIC card, with
> different IP address of my subnet.
> One card is used to see the internal network, the other, connected to the
> Cisco, to see the Internet.
> The Cisco has IP xxx.xxx.xxx.1
> The server has IP xxx.xxx.xxx.10 (internal, connected to an hub)
> The server has IP xxx.xxx.xxx.11 (external, connected to the router)
> I can see, from the server, the Internet and my internal network, but from
> the network I can't see the Internet and viceversa.
> I checked IP forwarding, but nothing happened.
> I Installed the RRAS from MS, activated the RIP, but nothing
> I set up my pc on the netowrk to use the xxx.xxx.xxx.10 as default gateway:
> I can ping this card from the network, but not the external one (NIC B).
> | |
> | |
> INTERNET =====CISCO==|==NIC A ---NIC B===| LAN
> | |
> | |
> I seems that the the routing doesn't happens.
> How can I use static route?
> I need to set as gateway for NIC A the CISCO and NIC B?
> I need to set as gateway for NIC N the NIC A?
> What about default gateway for the server?
> I need to modify my Router configuration?
> I need help because I read a lot, and it seems I made everithing right but
> it doesn't work.
> Thanks in advance.
> Sergio Novelli
> Please, write also in my mailbox, because next two weeks i'll be away.