MAC addresses in router vs Access Point

MAC addresses in router vs Access Point
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Subject Author Date
MAC addresses in router vs Access Point Ale 05-01-2008
Posted by jpd on May 6, 2008, 4:59 am
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> 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).

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.


> 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?

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.


> When I configure the router by the IP address on the LAN side, doesn't
> this need a MAC too?

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. :-)


--
j p d (at) d s b (dot) t u d e l f t (dot) n l .
This message was originally posted on Usenet in plain text.
Any other representation, additions, or changes do not have my
consent and may be a violation of international copyright law.

Posted by Ale on May 11, 2008, 4:56 am
>
> > 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).
>
> 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.
>
> > 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?
>
> 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.
>
this part was useful, thank you.

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other useful resources:
The Federal Communications Commission (FCC)
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Electronic and Software Security Products and Services
International Telecommunication Union

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