MAC addresses in router vs Access Point

wow, thanks for all the responses, but it's getting confusing now.

My soho wireless router has a label for a WLAN MAC and a LAN MAC. The LAN MAC is used on the WAN port (it gets an IP address assigned by the upstream router on its network). Why don't the 4 switch ports also need a MAC address? Or do they get the MAC of the device that's plugged into it? When I configure the router by the IP address on the LAN side, doesn't this need a MAC too?

The WLAN MAC is used on the WLAN. The LAN MAC is used on the LAN.

The WAN port one'd expect to be separate, but read on.

Devices never get the MAC of the port on the other side.

If you look around the various sites about toying around with home router thingies, you might see that some of those have a built-in ``switch'' with one internal and five external ports. One (logical) ethernet port to the rest of the device, five (LAN+WAN) physical outlets, and vlan logic to sort out what frame goes where.

The vlans might even be programmable. Usually stock firmware doesn't provide much facilities for this, but aftermarket custom firmware might.

This is not a hard and fast rule. Two counter-examples:

1) If the interface is not ethernet, it doesn't need an ethernet MAC, regardless of what other protocol (eg. IP) you're running on top of it.

2) Devices with only one ethernet address for the entire host, regardless of how many ethernet ports are in it (eg. sun hardware).

The second point has the drawback that you'll run into problems if more than one interface on the box is connected to the same broadcast domain.

The pros and cons of this have been discussed in more detail elsewhere, so I'll leave finding the precise explanation as an excercise. :-)

OK. Now you're calling a box with a modem and router inside as just a router. Most of us (the us's I know) think of a router as a device with an Ethernet WAN port. At least most in todays environment in terms of numbers.

But yes, a router with a non Ethernet WAN port would not have a MAC on the WAN port. But these are becoming a very small segment of the installed base.

David

DLR wrote: (snip)

Routers use with T1 lines have a serial interface that connects to a T1 CSU/DSU and then to a T1 line (two pair cable).

Even when T1 was popular, there should have been enough ethernet to ethernet routers within organizations such that routers with serial (T1) ports were relatively rare. Even more rare now.

There are some routers with built-in DSL modem or cable modem, but still not so common.

-- glen

Probably depends on the type of organisation. If all your branch offices happen to be small enough for a single router, and the uplinks to headquarters all happen to be T1s, then they'll likely outnumber the odd ``pure ethernet'' routing device at the head office.

That depends a bit on where you are, probably. There's more and more of them here. Those do tend to be ISP-delivered rather than sold directly to the customer. The ``dsl modem'' I have ``on loan'' from the ISP acts as a PPPoE-to-ATM ``bridge'', but could do routing and dhcp and a couple more tricks. It's not supposed to do that as it was delivered as a ``modem'', not a ``router''.

this part was useful, thank you.