Routing

Yes, there can be a bandwidth advantage to multi-homed servers if it's done correctly.

Each NIC needs to be connected to a separate collision domain (separate switch ports if using switches, separate router ports if using hubs and routers).

Each NIC will have a different IP address. The servers' clients will connect to a specific address, which will determine which NIC is used.

One example of the advantage of this configuration is where you have a separate backup server. The backup server might be configured to talk to one of the NICs, while regular clients use the other. While a backup is in progress, the regular clients won't see any increase in network congestion and probably won't notice that a backup is running. This would not be the case if you just had one NIC.

There are a couple of different reasons to have multiple NICs in a server.

A "multi-homed" server is configured to provide network services to more than one subnet so it primarily addresses routing and segmentation rather than bandwidth issues. In my environment, we use this strategy to allow a single server to efficiently serve two VLANs on different subnets.

Another reason to use multiple NICs is to increase bandwidth between the server and the network core. As one example, a Compaqserver and a Cisco switch can be configured to bond four FastEthernet full-duplex connections into a single virtual connection with a potential bandwidth of 800mbps.

A third reason might be to provide routing redundancy so if one path to the server fails, there is another path available. As with the first case, there is not a direct bandwidth advantage but there is a reliability advantage.

And finally, as the first answer suggested, a second NIC can be used to segregate backup traffic from production traffic and that has a definite bandwidth advantage.

So the answer to your question is: "It depends". And what it depends on is the rest of the system design.

paul

If you are using hubs, there can be an advantage in reducing collisions. For example, if your setup is as follows:
SubnetA <-> ServerAB <-> SubnetB <-> ServerBC <-> Subnet C
If nodes in subnet A rarely require resources from subnet B or C, then routing reduces traffic.

However, if you are using switches, I think that multi-homed servers are a waste. Switches create virtual dedicated networks.

Regardless of whether you are using hubs or switches, I would not configure a LAN with numerous multihomed servers. There is more administrative overhead, an increased chance of WINS corruption, and you are bound to have browser problems.

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