From: Justin Menga (Justin.Menga@xxxxxxxxxxxxxxxxxx)
Date: Thu Nov 02 2000 - 00:23:51 GMT-3
Hi,
The MSB in the SSAP is actually used for the Command/Response bit. The
remaining 7 bits are used for the actual SAP. The order is reversed due to
the non-canonical nature. Thus if you have a SAP of 4 (00001000), this
represents a SAP of 4 command. If you have a SAP of 5 (00001001), this
represents a SAP of 4 response.
In the DSAP, the MSB represents if the DSAP is an individual (0) or group
(1) DSAP. As far as I am aware, only 0 is used, hence the DSAP is never
unchanged.
Check out http://www.protocols.com/pbook/lan.htm#LLC to see the DSAP and
SSAP field representations.
Regards,
Justin Menga MCSE+I CCNP CCSE ASE
WAN Specialist
Computerland New Zealand
PO Box 3631, Auckland
DDI: (+64) 9 360 4864 Mobile: (+64) 25 349 599
mailto: justin.menga@computerland.co.nz
-----Original Message-----
From: Philip Lai [mailto:philip@home.com.hk]
Sent: Sunday, 29 October 2000 6:09 p.m.
To: ccielab@groupstudy.com
Subject: Sap type from Cisco technical tips.
Hi,
When I reading SAP type in
http://www.cisco.com/warp/customer/698/acl200.html , it list all the sap
type there.
I am wondering what the the meaning for the sap type for 00 and 01. Are they
the explorer frame or the command and respond ? Will the explorer frame have
a fixed value of sap type ?
________
Another point to consider when designing the ACL is that SAP values change
depending on if they are commands or responses. The SSAP includes the
command/response (C/R) bit to differentiate between them. The C/R is set to
0 for commands and to 1 for responses. Therefore, the ACL must allow or
block commands as well as responses. For example, sap 0x05 (used for
responses) is just SAP 0x04 with the C/R set to 1. The same applies to sap
0x09 (sap 0x08 with C/R set to 1), 0x0D, and 0x01.
Thanks
Philip Lai
NCR HK Email: philip.lai@ncr.com
Phone: (852) 2859-6076 Fax: (852) 2294-3055
This archive was generated by hypermail 2.1.4 : Thu Jun 13 2002 - 08:25:40 GMT-3