🚀 go-pugleaf

vjs@rhyolite.wpd.sgi.com (Vernon Schryver) writes:

>In article <mbt.718307170@Able.MKT.3Com.Com>, mbt@ESD.3Com.COM (Brad Turner) writes:
>> 
>I don't know about XNS or IPX, and I can't find any equivalent to the
>IP offset or MF bits in the "Internet Protocol" described in my old
>Xerox XNS documents.
 
Ahhh now we are talking about the same thing, my basic point is that "you
can't get there from here" within the context of bridging IPX or XNS
from FDDI to ethernet. The primative building blocks that exist within
IP that allow you to frag packets simply don't exist within the all
other protocol suites.
 
>The TCP sequence numbers have absolutely nothing to do with fragmenting
>TCP/IP, UDP/IP, or any other current IP protocol.  IP fragmenting is
>done entirely within the IP datagram, and is based on the 8-byte
>"offset" and the "more fragments" flag.
 
You're correct, I'm mixing my layers here, but the basic point about not
being able to fragment all protocols still hold true.
 
>The only IP fragmenting that an FDDI-ether bridge will usually need to
>do is of UDP packets.  UDP packets are datagrams, and have no sequence
>numbers of any kind.  If you don't have FDDI-ether-FDDI networks, the
>initial MSS negotiation in TCP will pick 1500.  This is consistent with
>the TCP/IP lore (and RFC) that considers fragmenting harmful.
 
Hmmm what about bulk transfers (e.g. FTP, SMTP) that are TCP based? If a
connection is to a local station (i.e. same net/subnet) won't the node
attempt to use max size packets of the native media for the TCP connection?
For example a FTP transfer from a FDDI station to an ethernet station that
is bridged. Won't the FDDI node attempt to use max size FDDI frames for the
transfer since the IP address of the destination is on the same net/subnet
as the FDDI station?
 
>Vernon Schryver,  vjs@sgi.com
 
 
-brad-
 

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Brad Turner | 5400 Bayfront Plaza  | Marketing Engineer   | (408) 764-5261
3Com Corp.  | Santa Clara CA, 95052| mbt@NSD.3Com.Com     | (408) 764-5002 fax