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Since almost all motherboards come with Ethernet ports, what's the purpose of having a separate network card in a server?

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up vote 8 down vote accepted
  1. Standardizing on a specific network card controller, so that you can reuse the same driver, and therefore maintain operating system image stability (for automated OS installation).

  2. Needing more ports than the (typically 2 or 4 ports) the server ships with.

  3. Needing or wanting a 'better' NIC than the server built-in, fx with better drivers, TCP offload engine, iSCSI boot capability, etc.

  4. Some things may look like network cards, but aren't really. Examples are remote management cards or RAID controllers with Ethernet interfaces for remote data gathering & management.

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+1 re-use a well-tested driver – Oskar Duveborn Dec 24 '10 at 0:27
+1, Additional NIC features are a MAJOR reason for adding even a single port. The built in NICs for the major server vendors are pretty good, but add-ins have extras they just can't fit in onboard. – sysadmin1138 Dec 24 '10 at 0:27
what would be a use case where a single server needs more than 1 port? Also can you give some examples of the extras you mentioned? – Esha Dec 24 '10 at 0:56
Servers can use multiple NICs to attach to back end networks like one dedicated to storage, database or backup. This keeps the load of those services off the front end network and allows better security. They can also use multiple front end ports to provide redundant connections in case of NIC failure. It happens more often than you would think when you have a room full of servers. – Chris Nava Dec 24 '10 at 3:37
Thanks. I have another Q: Can you connect two servers directly through ethernet? or do they both need to be connected to a router? – Esha Dec 24 '10 at 5:53

When I'm building VMware ESX servers we typically install between 12 and 14 Gigabit ports ( 2 for Management, 2 for vMotion, 2 for Fault Tolerant VM logging, 3-4 for iSCSI, 2-5 for production VM traffic). Even with 10Gbit on board NICs I like to have a couple extra so I can keep certain things fully isolated.

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One school of thought is that if a NIC goes out on a motherboard, you would have to replace the motherboard which is not as easy to do as replacing just a bad NIC.

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Except for the fact Helvick mentioned, that many times a whole lot more ports are needed than the integrated ones, many on-board network cards have really crappy drivers or in some other way limits throughput and/or increases latency (notably a bunch of HP servers used for electronic trading) so for services that rely on top-of-the-line network performance or low latency - add-in cards are sometimes the only reasonable solution, depending on what's integrated.

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They can be either multiport cards, special cards that offload the network processing from the CPU, or cards for specialized networks such as InfiniBand or 802.11.

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Some network cards even have tiny version of Linux on them.. Some companies might need very low latency for their networks.. so that is why a card with its own cpu/memory comes in handy.

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In the server world, It´s usual to have one nic for services and another one for administration. I mean, you always have a secure private network to administrate your servers through an especific LAN and a Service LAN where the server pushes its traffic to the firewall.

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