Multi-homing/Multiple IP addresses

When you have multiple ip addresses configured on a server, is there a way to specify one of the secondary ip address to be used as the source ip address, rather the primary?

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Claymoore

It's basic routing - Windows will use whatever card has the best route to the destination address as long as the addresses are on different subnets. You can also add static routes to the routing table and specify the interface to use.

pham0329

All the IP are on the same subnet. Static routes wont wont because they all exit out the same interface, to the same ip address. Perhaps an example will clear things up

NIC1

10.0.0.1 - primary
10.0.0.2
10.0.0.3

I want to source ip from 10.0.0.3, however, since 10.0.0.1 is the primary, all traffic shows up with a source ip of 10.0.0.1

Everyone

Change the binding order of the NICs. The NIC that is first on the binding order should get used first.

Zartanasaurus

Why do you have multiple NICs with IPs in the same subnet?

pham0329

I have ONE nic, with multiple IP addresses...

Everyone

pham0329 wrote: »

I have ONE nic, with multiple IP addresses...

Then NO. Traffic originating from the server will always appear to come from the primary IP. It will listen and respond on the other IPs you have configured, but everything it initiates will always come from the primary.

pham0329

That's what I figured...good to know. Thanks.

Everyone

pham0329 wrote: »

That's what I figured...good to know. Thanks.

FYI it's only "Multi-homing" if you have more than 1 NIC, and at least 1 of the NICs is configured to use a different default gateway than the others.

Lunchbocks

just for my own knowledge, why would you have multiple IP addresses attached to a NIC from the same subnet? Currently I have 7 IP addresses attached to my NIC, but they are from different subnets.

tex3030

Couldn't you be using multiple NIC for additional throughput? I would think that it should be all on the same address, but they would all still need to be on the same subnet.

MentholMoose

Lunchbocks wrote: »

just for my own knowledge, why would you have multiple IP addresses attached to a NIC from the same subnet? Currently I have 7 IP addresses attached to my NIC, but they are from different subnets.

One use case is a web server running multiple sites. Historially to use SSL you have needed a dedicated IP for each site due to how SSL works. The exception is if all the sites are subdomains of one domain name so all the sites can share a wildcard cert. There is a relatively new method called SNI that lets you have multiple SSL-enabled sites with their own certs on a single IP but it only works on relatively new servers and browsers.

Lunchbocks

Very good to know, thanks for the info.

creamy_stew

Everyone wrote: »

FYI it's only "Multi-homing" if you have more than 1 NIC, and at least 1 of the NICs is configured to use a different default gateway than the others.

Is it really a requirement that a different default gateway be configured? What's it called when you have two NICs/Networks and one DG?