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I am new to the world of networking and based on my readings there seems to be a definition of a 'true' router however am wanting to understand how do you tell if a router is a router? For example can I consider an off the shelf ADSL modem router a 'true' router? Does the OSI model matter when defining a router?

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Would appreciate if users comment on why they are voting to close the question. If I need to edit the question I will but I can't if you don't tell me what is wrong – PeanutsMonkey Nov 1 '11 at 19:02
In some conversations with my ISP, I have been told that I just have a (DSL) modem, rather than a "router", even though I know that the modem has DHCP, NAT and firewall capabilities. When they (and many others) say "router", they actually mean "wireless router". – sawdust Nov 1 '11 at 22:22
up vote 5 down vote accepted

A router contains contains a series of software which allows multiple computers to access the same internet connection with ease. So as long as it allows multiple computer connections and forwards "packets" from the internet to the proper computer, it is considered a router.

Don't know what considers a "true" router, but an ADSL modem gives you the ability to interface with the connection protocol your ISP provides you, this being your WAN port (like most routers do), so I guess this is a "true" router.

Most OSI models are the same through consumer routers, in this case, it only matters in inter-connecting devices. In your case, you obviously cannot connect an Ethernet port to your WAN port, as the cables are different.

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Thanks. So if an ADSL modem router does not support VLANs it would still be considered a router? – PeanutsMonkey Nov 1 '11 at 18:34
Yes it is still a router, VLAN is an extra feature to routers that allow remote computers (outside the WAN), to connect virtually as a LAN device and also receive a local IP address. – Steven Lu Nov 1 '11 at 18:37
Really? I thought VLANs were for subnetting local networks however big that local network may be e.g. two offices spread across the world – PeanutsMonkey Nov 1 '11 at 18:44
VLAN can be part of a subnet, but subnetting networks really just means of extending the available IP addresses for use, or organizing your network, etc. – Steven Lu Nov 1 '11 at 18:54
What do you mean by it only matters in inter-connecting devices? – PeanutsMonkey Nov 1 '11 at 18:58

A router is defined by routing network data between two subnetworks, which every ADSL router does (internal network and carrier network).

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Thanks so does it matter that a router can't subnet internal networks i.e. subnetting? – PeanutsMonkey Nov 1 '11 at 18:35
In theory, he can't as he must be configured as gateway for the machines in your internal subnet. In practise, this depends on the device and its software as it could just act like multiple routers, he must have multiple IP addresses (one in each internal subnet and one in the external) then.. – Jens Erat Nov 1 '11 at 18:57
Can you give me an example of a device that 'acts' like multiple routers? – PeanutsMonkey Nov 1 '11 at 19:04
You can configure every linux box like that. At least OpenWRT (which is based on linux) supports this for compatible off-the-shelf-routers, too; I guess also DD-WRT. – Jens Erat Nov 1 '11 at 19:39

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