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Posted by News Reader on May 1, 2008, 12:52 pm
glen herrmannsfeldt wrote:
> 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. That address was
> then used on all ports on that host. (Sun machines were
> often configured as routers with more than one ethernet port.)
Nice refresher.
>
> Since SOHO routers are sometimes used with systems that
> depend on a specific MAC address, such as some cable systems,
> they usually have the ability to specify the WAN port address.
> That address will, then, often be assigned the same value as
> one of the hosts on the LAN, so it should not be used on the
> LAN interface.
The MAC address "cloning" negates the need to reconfigure on the ISP's
side when the router is introduced to the topology, after a host was
previously connected directly to the ISP.
i.e.: The transition is transparent to the ISP because they still see
the original (now cloned) MAC address.
The cloned host with it's original MAC address can coexist since it and
the WAN interface (using the cloned MAC address) are on separate
collision domains.
>
> Do you know of any small routers that only have one MAC
> address?
>
> -- glen
>
Best Regards,
News Reader
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