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Is "gateway" a concept between two or more networks or a concept belonging to just one network?

When a device is connected to two networks, if it is listed as gateway in the routing tables of the hosts in one network, must it be not listed as gateway in the routing tables of the hosts in the other network?

Does a gateway device always have to be connected to a network where it is not a gateway? (So that the default routing table entry can route traffic to the network?)

Can a device be the gateway for each of the networks that it is connected to? If yes, is it correct that:

  • the default entry in its routing table will route to a network where it is a gateway?

  • the default routing entries in the hosts in that network route traffics back to the gateway?

  • when the gateway receives a packet with destination not in any network that it is connected to, there will be an infinite-loop of routing between the network and the gateway ?

Thanks.

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EDITED to match updated questions.

The term "gateway" is a functional definition. Practically speaking, the terms "gateway" and "router" are interchangeable.

Can a device connected to two networks be listed as gateway in the routing tables of the hosts in one network, but not in the other network?

It doesn't have to be, but in most cases, it is.

Does a gateway device always have to be connected to a network where it is not a gateway? (So that the default routing table entry can route traffic to the network?)

Seems to be the same question above.

Can a device be the gateway for each of the networks that it is connected to?

Yes

If yes, is it correct that: the default entry in its routing table will route to a network where it is a gateway?

The default entry (if there is one) will list a gateway (router) that will forward traffic to other networks not explicitly listed.

the default routing entries in the hosts in that network route traffics back to the gateway?

I'm not sure I understand your question. If there is only one gateway on a network, then it is likely (but not necessary) they all have that gateway listed as their default gateway.

when the gateway receives a packet with destination not in any network that it is connected to, there will be an infinite-loop of routing between the network and the gateway ?

The gateway (router) will look in its routing table to see which interface to use to forward the packet. If the destination address does not match any network in the routing table, the packet is dropped. Networks don't "route." Routers route.

  • Updated my answer. – Ron Trunk Mar 27 at 14:22

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