From: Earl Aboytes (earl@xxxxxxxxxxxx)
Date: Wed May 10 2000 - 01:11:54 GMT-3
All,
Here are my two cents on this subject. I have made this post before but I am p
osting it again for all the newbies.
The structure of the LLC header is such that you have 3 bytes made up of one by
te for DSAP one byte for SSAP and one byte for control. The SAP identifier is
actually only 7 bits long. The least significant bit in the DSAP and SSAP are
used for Individual/Group and Command/Response. In other words, in the first t
wo bytes you have I/G D D D D D D D C/R S S S S S S S where I/G and C/R stand f
or individual/group and command/response. When the I/G bit is set to one it is
set to group and this could mean that the packet is destined for more than one
operating environment in the attached system. If the c/r bit is set to one thi
s is a response as opposed to a command. We are always concerned about the a v
alue and then that value plus one.
SNA SAPs of 04/05, 08/09, and 0C/0D. This added value is the result of the I/G
bit being set on or off or the c/r bit being set on or off. Before you start
thinking that the I/G or C/R bit should be at the other end of the string, thin
k about non-canonical format.
EARL
---------- Original Message ----------------------------------
From: Muthu Mohanasundaram <mmsundar@yahoo.com>
Reply-To: Muthu Mohanasundaram <mmsundar@yahoo.com>
Date: Tue, 9 May 2000 17:51:35 -0700 (PDT)
>Hi Ben,
>
>The 0x0000 with a mask of 0x0D0D will include all the
>following SAPs:
>
>00 and 01
>
>04 and 05
>
>08 and 09
>
>0C and 0D
>
>which are exactly the SAPs for SNA.(00 is the Null
>SAP)
>
>Do it with binary, you will get it.
>
>This will permit all the SNA SAPs where as 0x0404
>0x0001 will only permit the 04 SAP.
>
>Anyone CMIIW (Correct Me If I am Wrong)
>
>Thanks,
>
>Mohan.
>
>
>
>
>
>
>--- Ben Rife <brife@bignet.net> wrote:
>> The following is from the source-route bridging
>> section of the CD:
>>
>>
>##############################################################################
##
>> An access list that passes a frame if it is a
>> NetBIOS frame (SAP = 0xF0F0)
>> An access list that passes a frame if it is an
>> SNA frame (SAP = 0x0404)
>> An access list that passes a MAC address of
>> 0110.2222.3333
>>
>> The following configuration allows for all these
>> conditions:
>>
>> ! Access list 201 passes NetBIOS frames (command or
>> response)
>> access-list 201 permit 0xF0F0 0x0001
>> !
>> access-list 202 permit 0x0404 0x0001 ! Permits SNA
>> frames (command or response)
>> access-list 202 permit 0x0004 0x0001 ! Permits SNA
>> Explorers with NULL DSAP
>> !
>> ! Access list 701 will permit the FEP MAC address
>> ! of 0110.2222.3333
>> access-list 701 permit 0110.2222.3333
>>
>> The 0x0001 mask allows command and response frames
>> to pass equally.
>>
>##############################################################################
##
>>
>> Note that it indicates that SNA frames are permitted
>> with 0X0404 0x0001 and
>> Netbios frames are permitted with 0xF0F0 0x0001.
>>
>> I understand the Netbios command and have infact
>> seen this in other documentation.
>> The SNA filtering command is new to me however. I
>> normally see it documented as 0x0000 0x0D0D.
>> Can someone confirm which is the correct form of the
>> SNA?
>>
>> Is it 0x0000 0x0D0D or 0x0404 0x0001? Can someone
>> explain?
>>
>> Thanks in advance,
>>
>> Ben
>>
>>
>
>
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