STREAMS implementation of TCP/IP and /etc/netd.cf questions

[Doug McCallum]

In article <tim.646580403 at holly> tim at delluk.uucp (Tim Wright) writes:
>In <9353 at bunny.GTE.COM> jdg0 at GTE.COM (Jose Diaz-Gonzalez) writes:
...
>Well here goes my shot at it. The 0x800 and 0x806 are the lsap values
>to be placed in the type field of the ethernet packet and are "IP" and

Right.  You covered things pretty well.  The LSAP field is either the
Ethernet type value or an IEEE 802.2 LSAP value.  This is meaningful
only for devices that support the concept.

>"ARP" respectively (no big surprise :-). The 0x1 and 0x101 are
>(quoting from the 1.1.2 manual) "module specific" and are used to
>inform the upper stream of the type of the lower stream. Currently
>these are the only values where 1 = IP stream on Ethernet, and 101 =
>ARP on Ethernet, i.e. they simply are simply ids for use by the arp

More specifically, the value is a two part value that fits in two bytes.
The most significant byte indicates the type of the STREAM below ARP.
A 0 is an IP STREAM and a 1 is an ARP STREAM.  The least significant
byte is a 1 for Ethernet.  The value used here is the value of the hardware
type field for ARP.  If you weren't using Ethernet you would have a differnet
value "N" to identify the hardware so would have types of "0xN and 0x10N"

>module. As to SLIP, the only lsap I have seen is 0x888 (with
>Interactive TCP/IP 1.2.0). This is apparently Xyplex (that's what the
>document I have says). I'm not clear how this fits in with ARP since a
>serial line is inherently not Multiple Access! Someone more familiar
>with SLIP will have to explain this - we don't have the internet here
>so SLIP is uncommon to say the least.

The SLIP driver uses the "llc" driver to do the underlying STREAMS Link Level
Interface protocol.  It requires an lsap to be specified.  The person that
implemented SLIP picked 0x888 at random.  It probably should have been a number
outside the range of Ethernet types, but it isn't.  It doesn't get used
other than to indicate that it is a SLIP STREAM.