From: Fred Ingham (fningham@xxxxxxxxxxxxxxxx)
Date: Tue Nov 13 2001 - 04:32:41 GMT-3
Brian: The IBM Redbook on LAN Architecture and Standards (available
online) also has SAP 08 and SAP 0c as "SNA". In looking at some AS400
configuration documentation the DSAP must be 04 when going to a FEP.
SAP 04 also appears to be a default. The SSAPs in examples are 04 and
08; in other examples the choices for a SSAP are 04, 08, 0c, 10, 14,
...
My conclusion, possibly wrong, is that SAPs 08 and 0c are generic SNA
SAPs that can be configured as SSAPs and have no specific meaning. SAP
04 is specific to SNA path control and is fixed in the 37xx NEP. The
last bit of a DSAP is the I/G bit, where a 0 is individual, and a 1 is
group. Hence DSAP 04 is SNA Path Control Individual, and DSAP 05 is SNA
Path Control Group. The last bit of a SSAP is the C/R bit, where 0 is
command and 1 is response.
As an aside, the second to last bit in a SAP is the user/standard bit
where 0 is user and 1 is standard. For all SNA SAPs this bit is 0.
Also recall that SNA uses the null SAP when the SSAP/DSAP is not known.
This is used for XID and TEST frames only.
So when we filter every posssible SNA SAP we use 00 00 0D 0D, which
covers 00, 01, 04,05,08,09,0c and 0d. I suspect if you are asked to
filter a SAP(s) it(they) will be specified since the 00 00 0D 0D is well
known.
HTH, Fred.
Brian Hescock wrote:
>
> Anyone have a reference that says what saps 08 and 0C are other than
> just "SNA"? For example, sap 04 is for "SNA Path Control Individual".
> All I find for 08 and 0C is "SNA". I need to know what specifically 08
> and 0C are for in case I get a question that is rather specific as to
> what SNA saps I need to block. I've searched the archive and CCO for
> quite some time but each reference I've found doesn't specify *exactly*
> what 08 and 0C are used for (other than just "SNA"). There's abviously
> a specific function for them, otherwise we wouldn't usually use mask
> 0x0D0D to include 08 and 0C also. Thanks,
>
> Brian
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