If you have a Mac with more than one Ethernet port and you’re finding that you have a need for greater network bandwidth, then you can combine them into one virtual Ethernet port. This is known as “link aggregation”. The combined Ethernet ports appear as a single IP address to your computer and applications.
Combining ports provides increased bandwidth by merging the bandwidth of the individual ports. This also provides for load-balancing your network traffic and providing for an automatic network failover in the event that you have an individual ethernet port or cable that fails (the other port/cable picks up the rerouted traffic, though your bandwidth is now reduced to what the single port or cable can bear.)
Here’s how you can set this up on your own Mac with two built-in ethernet ports :
1. Open System Preferences
2. Go to System Preferences -> Network
3. Select the small cog in the bottom left side (next to the + and –) and choose Manage Virtual Interfaces…
4. Select the + in the bottom left and choose New Link Aggregate…
5. Then you select the two Ethernet interfaces and name the new interface whatever you want. Once finished, click the Create button.
6. After that it will appear in the network list as one network interface with a bond ID.
7. Click Apply to activate the new virtual Ethernet service.
Apple also has a KBase article available on this subject: http://support.apple.com/kb/PH8356