Why are there two ethernet ports on my Mac Pro?

The second port could be used for a high-speed (1 Gbps) link between computers and file servers while the first is used for internet. Internet modems don't have 1 GBPS ports, so sharing one port on the computer would reduce the bandwidth available for file transfers.

You can connect to two different networks at the same time, or to one network with (almost) twice the bandwidth.

Hi, how do I connect two network cables to my router? Just as I would connect two computers?

Thanks

You probably can't do it with your router, and anyway there would be no point. Your router connects you to the Internet, and Internet speeds are far lower than what a single Ethernet link can handle. Some high-end Ethernet switches allow link aggregation. That's for connecting between local networks.

Practically speaking, the only real use of the two Ethernet ports to you would be to use the Mac Pro itself as your router. I do that, and it works well, but the setup is very complex.

I think that the real reason there are two was to support XSAN. One port for the "private" storage network and one port for the "public" network.

The two ports can be used for link aggregation. You bond the ports together to get a 2Gbps network. This will only be helpful for your internal LAN, as nobody I know of has an internet connection like that.

In order to use link aggregation, you will need some external hardware, specifically an intelligent switch. The switch can be configured to aggregate two of the ports into a single logical connection. I have a Netgear GS724T-300, as well as an 8 port version. The 8 and 16 port versions can only have 2 aggregate links, while the 24 port can have 4.

So, if you have two ethernet cables from your mac pro to the switch, and have a few other computers in your house (like I do), then your server can move data faster between multiple clients.

The other think you can do, is get a NAS that has dual links, and then you can plug the NAS into two switch ports and aggregate that also. Now you have a 2Gb/s link between your server and your NAS, which allows the server to move data much faster.

Most commonly, probably "share my internet connection" with a 2nd computer instead of going thru a router or if there is no router port available.