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Say we have a router that connects to other routers and they connect to lan networks, does that router have a network card for each router it connects with but a single forwarding table for all? or even each network card has its own forwarding table?

Or a more simple case where a router that connects between two LANs like in the picture below.

Since we see that each side has a different mac address, I'm led to believe that it has at least two network cards, but wouldn't that mean if we have for example a router that connects hundreds of other routers or networks, does it also have hundreds of network cards?

enter image description here

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  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
    – Ron Maupin
    Aug 14 '17 at 20:59
  • Questions should decay after a while so they don't keep poping up, @RonMaupin
    – shinzou
    Aug 14 '17 at 21:23
  • We get a lot of questions that get bumped to the top (about a dozen so far today, and many more over the weekend), and people have asked me to do something about it. I have gotten dozens and dozens of accepted answer for question with answers, but no accepted answers. It is also courteous to the people that have taken the time to provide answers to accept one that has helped you.
    – Ron Maupin
    Aug 14 '17 at 21:26
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A router (or routing instance) will have a single layer-3 forwarding table for all interfaces, not one per NIC. Except for an aggregation router as used in an ISP (which will not necessarily be Ethernet, so your ideas about NICs probably don't apply), most routers (as opposed to L3 switches) will have only a few or a few tens of IP subnets attached.

Where you may find very many subnets is with a L3 switch such as in a large data centre, and these may have hundreds of ports (possibly distributed across multiple racks) but will also have dot1q VLAN tags on many ports as mentioned by Viktor. However in this case the L3 interface is not associated with any physical port, and the MAC address used for each L3 interface will be defined by software.

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Single card can have multiple interfaces. In addition to that on a single interface you can use do1q tagging and transport multiple services over 1 physical link.

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