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When looking at the contents of a routing table section on the Wikipedia article on Routing Tables, it contains a table as an example of a routing table with two headings which have an unclear distinction to me: Gateway and Interface.

I believe a gateway is where a packet is forwarded to by the router. If this is the case, what is the Interface column? If this is not, what is the Gateway column representing, particularly in comparison with the Interface column?

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  • A gateway is a host on the network that knows how to forward traffic to other networks. That is almost always a router. There may be other reasons for having a gateway other than a router, e.g. a proxy, but you are not to the point of needing to worry about that right now.
    – Ron Maupin ♦
    May 8, 2018 at 19:07
  • 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 can post and accept your own answer.
    – Ron Maupin ♦
    Jan 3, 2021 at 4:22
  • @RonMaupin Hi Ron, none of the answers have left me confidently understanding the difference(and in any case it appears this is the case for many others judging by the question votes compared to the answer votes). I still don't understand what the table is trying to convey, despite now having a much better understanding of corporate networks, IP, ARP, routing, etc., so cannot add my own answer.
    – Alex W
    Jan 4, 2021 at 9:11

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An interface is a connection to a local segment. Generally, it's a network interface or port (layer 1 and 2). A single network port may have multiple IP addresses and represent multiple layer-3 interfaces though. Using VLAN tags (802.1Q), it may also represent multiple layer-2 interfaces.

A gateway is a potential path to a remote network. It needs to be in reach of one or more interfaces, ie. be part of the same segment and subnet. The default gateway is the path to 'everything we don't have a better path for'.

Gateway is the functional name from the perspective of a local segment where a gateway leads 'elsewhere'. Router is the very same thing from the overall perspective of the larger network - a connection between two or more subnets.

Now, the interface in a routing table is that interface which is to be used to talk to the given gateway. A host may have multiple interfaces with the connecting segment and normally chooses the one with the highest link speed (lowest metric).

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  • Just a clarification here port = network device. For anyone coming from software engg background the term port brings Transport layer port to mind.
    – Akshay Hiremath
    Nov 29, 2020 at 2:01
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    Let's say "port on a network device" - a device can have many ports.
    – Zac67 ♦
    Nov 29, 2020 at 8:16
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In this example, the address in the interface column is used to identify the particular interface (your computer may have more than one). Since naming conventions often depend on hardware, it is easier to identify them by IP address.

For example, your routing table shows the default gateway is 192.168.0.1, and it can be reached by using the interface that has the IP address 192.168.0.100.

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    Could you give a physical/practical example of the difference, such as in a standard home network?
    – Alex W
    May 8, 2018 at 19:02
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    @AlexW, home networking is explicitly off-topic here. Based on all your questions, you are trying to learn network engineering, and if you try to look at it from the perspective of home networking and consumer-grade devices, you can end up very confused. Learn the basics first, and you can see how they relate to something like home networking later, but forget about home networking and consumer-grade devices until you have a good understanding of networking.
    – Ron Maupin ♦
    May 8, 2018 at 19:06
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    @RonMaupin Noted. I think I'd really benefit with a physical example to latch onto, but if you're sure that's not feasible or appropriate for such questions, I accept that.
    – Alex W
    May 8, 2018 at 19:27
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    @AlexW IP routing tables assume the device has multiple network interfaces, although most PCs have only one. When there is more than one, the device needs to know which interface to use to reach the gateway. The interface column defines that. In the context of home networking, only your router has more than one interface.
    – Ron Trunk
    May 8, 2018 at 21:03

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