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A router is a device that forwards between networks. A gateway is a forwarder within the local network, allowing communication with another network.

Essentially, both are the very same thing, just the perspective varies.

if a client needs to send a packet to another which is not in the same ip segment it sends the packet to the gateway, behind which usually a router takes over.

If you understand the gateway as the IP address/interface you pass data to other networks to, and the router as the device that interface is attached to, then that is basically correct.

what do I need the gateway for?

You need a gateway to communicate with hosts that are not part of your local subnet.

Or is gateway just a term to describe the default router

The default gateway or default router that the default route is the gateway you pass data that you don't have a better route for. Basic hosts use a default gateway to pass all their non-local traffic to.

a gateway can also be used to translate between something like ethernet and fiber)?

Not only the physical layer (copper, fiber, wireless) but also the data link layer (Ethernet, virtual, ATM, FDDI, ...) can be vastly different behind the gateway. The beauty of it is that you don't need to care, only that it supports IP.

Could I just plug one (or more) routers into a network without specifying a gateway?

Routers generally need some kind of configuration - but you can use a very simple configuration if you don't connect to larger networks or the global Internet.

A router is a device that forwards between networks. A gateway is a forwarder within the local network, allowing communication with another network.

Essentially, both are the very same thing, just the perspective varies.

if a client needs to send a packet to another which is not in the same ip segment it sends the packet to the gateway, behind which usually a router takes over.

If you understand the gateway as the IP address/interface you pass data to other networks to, and the router as the device that interface is attached to, then that is basically correct.

what do I need the gateway for?

You need a gateway to communicate with hosts that are not part of your local subnet.

Or is gateway just a term to describe the default router

The default gateway or default router for the default route is the gateway you pass data that you don't have a better route for. Basic hosts use only a default gateway to pass all their non-local traffic to. More complex hosts may use a number of different gateways with more specific routes.

a gateway can also be used to translate between something like ethernet and fiber)?

Not only the medium (copper, fiber, wireless, virtual), physical layer protocol (Ethernet, xDSL, 802.11, avian carrier, ...), but also the data link layer (IEEE 802 family, ATM, FDDI, ...) can be vastly different behind a gateway. The beauty of it is that you don't need to care, only that it supports IP. There's no real translation, just changing underlying networks.

Could I just plug one (or more) routers into a network without specifying a gateway?

Routers generally need some kind of configuration - but you can use a very simple configuration if you don't connect to larger networks or the global Internet.

A router is a device that forwards between networks. A gateway is a forwarder within the local network, allowing communication with another network.

Essentially, both are the very same thing, just the perspective varies.

if a client needs to send a packet to another which is not in the same ip segment it sends the packet to the gateway, behind which usually a router takes over.

If you understand the gateway as the IP address/interface you pass data to other networks to, and the router as the device that interface is attached to, then that is basically correct.

what do I need the gateway for?

You need a gateway to communicate with hosts that are not part of your local subnet.

Or is gateway just a term to describe the default router

The default gateway or default router that the default route is the gateway you pass data that you don't have a better route for. Basic hosts use a default gateway to pass all their non-local traffic to.

a gateway can also be used to translate between something like ethernet and fiber)?

Not only the physical layer (copper, fiber, wireless) but also the data link layer (Ethernet, ATM, FDDI, ...) can be vastly different behind the gateway. The beauty of it is that you don't need to care, only that it supports IP.

Could I just plug one (or more) routers into a network without specifying a gateway?

Routers generally need some kind of configuration - but you can use a very simple configuration if you don't connect to larger networks or the global Internet.

A router is a device that forwards between networks. A gateway is a forwarder within the local network, allowing communication with another network.

Essentially, both are the very same thing, just the perspective varies.

if a client needs to send a packet to another which is not in the same ip segment it sends the packet to the gateway, behind which usually a router takes over.

If you understand the gateway as the IP address/interface you pass data to other networks to, and the router as the device that interface is attached to, then that is basically correct.

what do I need the gateway for?

You need a gateway to communicate with hosts that are not part of your local subnet.

Or is gateway just a term to describe the default router

The default gateway or default router that the default route is the gateway you pass data that you don't have a better route for. Basic hosts use a default gateway to pass all their non-local traffic to.

a gateway can also be used to translate between something like ethernet and fiber)?

Not only the physical layer (copper, fiber, wireless) but also the data link layer (Ethernet, virtual, ATM, FDDI, ...) can be vastly different behind the gateway. The beauty of it is that you don't need to care, only that it supports IP.

Could I just plug one (or more) routers into a network without specifying a gateway?

Routers generally need some kind of configuration - but you can use a very simple configuration if you don't connect to larger networks or the global Internet.

A router is a device that forwards between networks. A gateway is a forwarder within the local network, allowing communication with another network.

Essentially, both are the very same thing, just the point of view varies.

A router is a device that forwards between networks. A gateway is a forwarder within the local network, allowing communication with another network.

Essentially, both are the very same thing, just the perspective varies.

if a client needs to send a packet to another which is not in the same ip segment it sends the packet to the gateway, behind which usually a router takes over.

If you understand the gateway as the IP address/interface you pass data to other networks to, and the router as the device that interface is attached to, then that is basically correct.

what do I need the gateway for?

You need a gateway to communicate with hosts that are not part of your local subnet.

Or is gateway just a term to describe the default router

The default gateway or default router that the default route is the gateway you pass data that you don't have a better route for. Basic hosts use a default gateway to pass all their non-local traffic to.

a gateway can also be used to translate between something like ethernet and fiber)?

Not only the physical layer (copper, fiber, wireless) but also the data link layer (Ethernet, ATM, FDDI, ...) can be vastly different behind the gateway. The beauty of it is that you don't need to care, only that it supports IP.

Could I just plug one (or more) routers into a network without specifying a gateway?

Routers generally need some kind of configuration - but you can use a very simple configuration if you don't connect to larger networks or the global Internet.