2

My question may be too basic and factual for this site, but I was reading about subnetting from our textbook which gives following example:

enter image description here

As it shows, the router itself occupies an address on each subnet. However, in the textual explanation, nowhere this fact is specified in words; it's just that in the diagram where I noticed this.

Is it always the case that the router uses an address in each of the subnets to which it is connected?

2

A router must get, on its interfaces which face each subnet, an IP address in the address range of this subnet. This interface IP is called the gateway from the perspective of the devices on the subnet, so you will actually find this expression is more popular .

2

A simple router always will use an address on the networks that it is connected, cause it will work like a GATEWAY fot the equipments of that subnet.

On modular routers, big routers that you can encounter on ISP or Tier1 or Tier2 places, port can be configured like router or switchports, and then, with your configuration in mind, you can decide to put or not and address. Remember, an address is the diference to work on Layer 2 or Layer 3.

1

A router is just another element in the subnet, so it needs to have an address belonging to the subnet, otherwise, how could devices in the network be aware of its presence?

1

Yes. All devices on an IP network need an IP address, including routers. In your example, the router has actually 3 visible IP addresses and one more at the bottom of the diagram (x.y.z.t/n).

The router IP address in this example serves as the default gateway for each of the subnets:

Subnet 1: Default GW = 17.12.14.2, subnet mask is 255.255.255.224 (/27)
Subnet 2: Default GW = 17.12.14.34, subnet mask is 255.255.255.240 (/28)
Subnet 3: Default GW = 17.12.14.50, subnet mask is 255.255.255.240 (/28)

Despite I said all devices on an IP network need an IP address, the devices which need an IP are all L3 capable devices (see OSI model). L2 devices, such as switches, do not necessarily need an IP address. For management purposes they usually do have an IP address, though.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.