What is IP Forwarding and when do I use it?

[RCNetAdmin]

What is IP Forwarding and when do I use it?

 

[bcastner]

Both bridging and IP Forwarding allow XP to act as a router between subnets. You would use this if you have two different network segments and you need to have traffic from both available. This is particularly useful if the two network segments are of different media types.

The network bridge allows you to connect LAN segments by selecting the appropriate network connection icons and clicking Bridge Connections. Similar buttons allow you to enable the bridge and add connections to it. The network bridge manages your LAN segments and creates a single subnet for the entire network. There is no configuration required, and you do not need purchase additional hardware such as routers or bridges. IP addressing, address allocation, and name resolution is highly simplified in a single subnet IP network.

The network bridge can create connections between different types of network media. In a traditional network, if you are using mixed media types you need a separate subnet for each type of media, and packet forwarding is required between each one of the network's multiple subnets. Packet forwarding is required because different protocols are used for different types of media. Network Bridge automates the configuration that is required in order to forward information from one type of media to another.

If you just need to enable Netbios traffic, you can use the XP native support for Bridging. For TCP/IP you need to make a registry entry to enable IP forwarding.

Set this key to 1 to enable routing, or 0 to disable (disabled is the default):
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\IPEnableRouter

See:

http://www.microsoft.com/technet/treeview/default.asp?url=/technet/columns/cableguy/cg0102.asp

 

[victorv]

Suppose you have 2 NETs in your company with no
physical connection

NET A:
net=192.168.1.0 NM=255.255.255.0 DG=192.168.1.251

NET B:
net=192.168.2.0 NM=255.255.255.0 DG=192.168.2.251

192.168.1.251 and 192.168.2.251 are 2 routers one for
each network

If you ping a PC of NET B from one of the NET A you see timeout.

The best way to understand this is to think your
Pc with 2 nics (also if it is not mandatory).

you wire nic 1 on Lan A and give IpAd = 192.168.1.100
you wire nic 2 on Lan B and give IpAd = 192.168.2.100

Now the 2 network are linked by your PC :
from your PC you can ping address of both net, but other PC
of NET A cannot still see PC of NET B.

In one PC of net A, you can add a another gateway putting the adress of your PC (192.168.1.100)

In one PC of net B, you can add a another gateway and you
can put the 2nd adress of your PC (192.168.2.100)

If you activate IP-Forwarding, (probably you have a NT4)
your PC can acts as router between networks.

If this is clear, think that the 2 networks can be on the
same lan ( just 1 hub whith machines on diff networks)
and your pc may have just 1 nic with 2 ip address.

bye