Charles Hedrick (firstname.lastname@example.org)
23 Apr 88 02:18:37 GMT
In article <In article <6140@shamash.UUCP> In article <6140@shamash.UUCP> jwabik@shamash.UUCP (Jeff Wabik) writes:
> Does anyone know which version of tcp-ip is implemented in the standard
> Sun OS (Sun UNIX 3.x) ? 802.2? 802.2/snap? 802.3?
The wording of this question is not perhaps as precise as it might be.
TCP/IP as a protocol suite covers OSI layers 3 and above. The 802
things you cite are at layers 2 and below. So whether or not of 802.2
is used, with or without SNAP's, is not really a matter of the version
of TCP/IP. The way IP works is that there is a standard for how to
run it on each particular type of network medium. This is referred to
as an "encapsulation", since normally what happens is that the IP
packets get encapsulated in a packet appropriate to the medium. So
whether 802.2 is used is a question of the particular encapsulation
used, not the version of IP used.
There is an official IP encapsulation for 802-type networks. It is
defined by RFC 1042. It supports 802.2 LLC and SNAP over 802.3, .4,
and .5 networks. However this is a new RFC, defined primarily for the
benefit of IBM token ring and similar new 802 technologies. In fact
the "traditional" TCP/IP medium is Ethernet, as opposed to 802.3, and
this is what Sun supports. Of course there's very little difference
between Ethernet and 802.3. The main one is that what Ethernet calls
a type field, 802.3 calls a length field. The IP encapsulation for
Ethernet uses the type field to identify the packets as IP packets.
This encapsulation has a bare minimum of overhead. The Ethernet
headers are put immediately in front of the IP headers. So you've
just got Ethernet addresses and a type code identifying the packet as
IP. No LLC or SNAP type stuff is used. (There is also a different
Ethernet type code used for a secondary protocol called ARP. This
protocol is used to map from IP address to Ethernet address. This
protocol is officially considered part of the Ethernet encapsulation
specification.) Suns normally use this Ethernet encapsulation, not
the newer 802-style encapsulation.
Of course the defined Ethernet types are large enough that they do not
form legal 802.3 packet lengths, so in fact there's no reason that a
single cable can't carry both types of protocol. Indeed in theory one
could have two separate (and non-communicating) TCP/IP networks on the
same cable, one using the traditional Ethernet encapsulation, and the
other using the new 802-style encapsulation. However so far I haven't
seen 802-style encapsulations used on Ethernet or 802.3, except by HP
(who designed a different encapsulation that apparently only HP and
cisco implemented) and cisco (who implement all three encapsulations:
Ethernet, the HP version, and the new 802.3 standard). In general the
TCP/IP community is really using Ethernet version 2, not IEEE, except
to the extent that IEEE happens to be compatible with Ethernet. This
may change over time, as other 802 networks become more common. At
the moment the same is true of DECnet, XNS, and other network
protocols that we see on our cables.
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