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 DLR on May 7, 2008, 6:33 pm
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Steinar Haug wrote:
>>>> Yes, but not if it used the same MAC on both the WAN and LAN
>>>> ports, as seems to be allowed for IP routers.
>>> On a WAN port, a router often does not use ethernet framing at all.
>>> In these cases no (ethernet) MAC address is used on the WAN port.
>> Excuse me?!?!?
>
> Read up on (for instance) serial links and PPP encapsulation. No MAC
> address is used.

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

Posted by glen herrmannsfeldt on May 7, 2008, 7:49 pm
DLR wrote:
(snip)

> 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.

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).

> 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.

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


Posted by jpd on May 8, 2008, 3:06 am
On Wed, 07 May 2008 15:49:08 -0800,
> 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.

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.


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

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''.


--
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 Albert Manfredi on May 1, 2008, 2:18 pm

> Ale wrote:
> > why does an access point have 2 MAC addresses (one WLAN, one LAN)
> > while a router has only one even if it has lan ports and wan ports?
>
> Somewhere back in the origins of ethernet is the ability to
> assign MAC addresses either to ports or hosts.
>
> The only one I know to commonly apply them to hosts is Sun,
> which used to put the address in ROM on the CPU board which
> may or may not have an ethernet interface. =A0That address was
> then used on all ports on that host. =A0(Sun machines were
> often configured as routers with more than one ethernet port.)

That was also my reaction to the original post. It is possible that
the router might have only one MAC address assigned to it, if it
follows that somewhat iffy (IMO) Sun philosophy you mention.

Note this, however. Access Points are not necessarily combined with a
router function. Therefore, the two interfaces of an access point
*could* exist within the same network (IP subnet). Whereas the two
interfaces of the router would, by definition, each be in its own IP
subnet.

Therefore, it's acceptable to assign just one MAC address to a router,
but not to the access point.

Another minor point is that sometimes switches use the MAC address of
one of their interfaces as the MAC of the entire box, if a single MAC
address to identify the box is needed. I'm too lazy to look it up
right now, but doesn't RSTP do this, for example?

Bert

Posted by glen herrmannsfeldt on May 1, 2008, 3:14 pm
Albert Manfredi wrote:

(snip)

>>Somewhere back in the origins of ethernet is the ability to
>>assign MAC addresses either to ports or hosts.

>>The only one I know to commonly apply them to hosts is Sun,
>>which used to put the address in ROM on the CPU board which
>>may or may not have an ethernet interface. That address was
>>then used on all ports on that host. (Sun machines were
>>often configured as routers with more than one ethernet port.)

> That was also my reaction to the original post. It is possible that
> the router might have only one MAC address assigned to it, if it
> follows that somewhat iffy (IMO) Sun philosophy you mention.

> Note this, however. Access Points are not necessarily combined with a
> router function. Therefore, the two interfaces of an access point
> *could* exist within the same network (IP subnet). Whereas the two
> interfaces of the router would, by definition, each be in its own IP
> subnet.

> Therefore, it's acceptable to assign just one MAC address to a router,
> but not to the access point.

> Another minor point is that sometimes switches use the MAC address of
> one of their interfaces as the MAC of the entire box, if a single MAC
> address to identify the box is needed. I'm too lazy to look it up
> right now, but doesn't RSTP do this, for example?

So it would be just a bridge. I have thought about connecting just
to the LAN port on a router/access point to put the WLAN on the same
subnet as an existing wired LAN.

Does a switch without spanning-tree need any MAC address? If so,
does it need more than one?

-- glen


But without a router function, why two addresses?


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