An ordinary computer has one network card and that is enough. But servers, NAS units and some workstations have two or more. What is it for and how do you use both at once? Let us explain the options and when it makes sense.

What two network cards are for

Two network cards (NICs) open up several practical options:

  • Higher throughput by joining the cards together.
  • Connection backup (redundancy) when one card or cable fails.
  • Separating two networks on a single machine.
  • Routing and sharing a connection between networks.

Each of these options is suited to something different.

1. Joining cards for speed and backup (bonding)

The best-known use is bonding, that is joining two cards into one logical connection. Depending on the chosen method, you get either higher throughput, or a backup, or both. The topic is covered in detail in a separate article on what bonding and link aggregation are.

Bonding is useful, for example, for a server or NAS accessed by many people at once, or where the connection must not drop.

2. Separating two networks

The second common use is connecting a computer to two separate networks at the same time. Examples:

  • A server on the production and backup network at once.
  • A machine connected to the ordinary and camera network without linking them.
  • Separating the trusted and guest network, a similar principle to network separation via VLAN.

The important thing is that the networks stay separate and traffic does not flow freely between them, which is also safer.

3. Sharing and routing a connection

A computer with two cards can act as a gateway or router: connected to the internet by one card, handing out the connection to the local network by the other. This is how a home server or a firewall built on a computer works.

What to watch for

  • It has to be set up correctly. Two cards on the same network without configuration can cause conflicts.
  • Bonding requires switch support for some methods.
  • When separating networks, make sure they are not linked unintentionally through this computer.

When it makes sense

  • Servers and NAS, where speed and reliability matter.
  • Workstations with large data transfers.
  • Machines at the border of two networks (gateway, firewall).

For an ordinary home computer, one card is enough. If your motherboard’s network card has failed, the article on a laptop without a network card offers a solution, the principle of an add-on card is the same.

Dealing with a server, NAS or network where speed and backup matter? Get in touch, we will design and set up the wiring to measure.