From: Fred Ingham (fingham@cox.net)
Date: Mon Sep 02 2002 - 16:17:25 GMT-3
Raj: The statement in the Caslow/Pavlichenko book p.744 is " When filtering
Token-Ring MAC addresses use the mask 8000.0000.0000 for the source address
of any traffic that requires an exact match and needs to be source-route
bridged."
The next sentence tells why: " The high-order bit is set to one to provide
for the different values of the routing information indicator."
First of all this is only applicable to access lists where the source MAC
address can be specified (for example 1100-1199)..
Secondly, since the context is source-route bridging on Token-ring, you need
to know that the high order bit in the Token-ring source MAC address is
called the RII bit and is set to 1 when there is routing (RIF) information
in the frame and 0 when there is no routing information in the frame. Since
the high order bit can be either a 1 or a 0, the mask is set to allow
either.
On the doc CD or on CCO under source-route bridging/ access-list, the
statement is: "For source address filtering, the mask always should have the
high-order bit set. This is because the IEEE 802 standard uses this bit to
indicate whether a RIF is present, not as part of the source address."
Cheers, Fred
----- Original Message -----
From: "Raj Bahad" <raj.bahad@totalise.co.uk>
To: <ccielab@groupstudy.com>
Sent: Saturday, August 31, 2002 4:40 PM
Subject: Mac Address
> Hi Group,
>
> Can someone explain to me the function of 8000.0000.0000 as a mask for a
> specific host.
>
> I've searched CCO but am unable to find a specific answer...Caslow's book
> actually recommends this approach, however, does not really explain why!
>
> Any help will be greatly appreciated!
>
> Raj.
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