From: Brian Hescock (bhescock@xxxxxxxxx)
Date: Thu Nov 29 2001 - 16:51:06 GMT-3
Fred,
I guess what was throwing me off is the examples for explorers use 0x0004
0x0001, although 0x0004 0x0101 would work too I would expect (null dsap and
response).
Brian
Fred Ingham wrote:
> Brian: From a previous post (edited):
>
> The last bit of a SSAP is the C/R bit, where 0 is command and 1 is
> response.
> (as you noted)
>
> 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. (so you need 0d to cover group DSAPs).
>
> I'm guessing that NetBIOS, and IPX (F0 and E0) also use group DSAPs,
> hence the
> 01 01 mask.
>
> HTH, Fred.
>
> Brian Hescock wrote:
> >
> > We usually see SNA filtered with 0x0000 0x0D0D but...
> >
> > Based upon all of the examples I've seen on CCO, as shown below, we only
> > need to worry about the response for the SSAP (mask 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
> >
> > So, given that, isn't 0x0000 0x0C0D technically more correct than 0x0000
> > 0x0D0D since we only worry about the response for the SSAP?
> >
> > Also, if for SNA we only change the SSAP for the response (0x0404
> > 0x0001), why do examples for Netbios and IPX use a mask of 0x0101 (as
> > in 0xF0F0 0x0101 and 0xE0E0 0x0101)? Every doc I've seen on CCO is
> > consistent with regards to difference between SNA and netbios / ipx, any
> > idea why the difference in the mask?
> >
> > Brian
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