raj@hpindwa.HP.COM (Rick Jones) (06/29/90)
a toss-up question... What size of packets will vendor x's tcp/ip over token ring tend to send out onto the wire? I realize that the theory says it could be upwards of ~4K for 4Mbs and ~17K for 16Mbs (corrections welcomed;-), but what sizes might I realisticly see if I were to stick an analyzer on a TRN today, and oh, say, 2 years from today... inquiringly, rick jones stardard disclaimers, and standard promises to summarize to the net etc...
jbvb@VAX.FTP.COM (James B. Van Bokkelen) (06/30/90)
>What size of packets will vendor x's tcp/ip over token ring tend to >send out onto the wire?..... At one point, there seemed to be a general consensus of the IBM implementations that the length indicated in the RIF was to be 2052 bytes (in fact, some of them insisted on it). This may have changed, but people who coded to suit it may not have. James B. VanBokkelen 26 Princess St., Wakefield, MA 01880 FTP Software Inc. voice: (617) 246-0900 fax: (617) 246-0901
CSYSMAS@OAC.UCLA.EDU (Michael Stein) (06/30/90)
> >What size of packets will vendor x's tcp/ip over token ring tend to > >send out onto the wire?..... > > At one point, there seemed to be a general consensus of the IBM > implementations that the length indicated in the RIF was to be 2052 > bytes (in fact, some of them insisted on it). This may have > changed, but people who coded to suit it may not have. Watch out! What the RIF says and what you really want to do may be different things. An example is a RIF which says 2052 where there are routers to Ethernet (max IP packet size of 1500). Any IP packet larger than 1500 will get fragmented. Using a RIF size of 1500 (then next smaller than 2052) is worse but for the other direction. A 1500 byte RIF size only allows 1500-8 => 1492 bytes of IP packet (8 bytes are used for the IEEE stuff on TR, but not on Ethernet) and will result in full size Ethernet packets being fragmented on Token Ring. PS: Some Token Ring support is leaning toward 4 to 8 K packets...
jbvb@VAX.FTP.COM (James Van Bokkelen) (07/02/90)
Date: Fri, 29 Jun 90 15:41 PDT From: Michael Stein <CSYSMAS@OAC.UCLA.EDU> An example is a RIF which says 2052 where there are routers to Ethernet (max IP packet size of 1500). Any IP packet larger than 1500 will get fragmented. Most modern TCP implementations have Maximum Segment Size option handling which attempts to avoid fragmentation when traversing routers. If the transport protocol you're concerned with is layered on UDP, you are likely to find that you must tweak things manually. At any rate, what I was saying was that there was a time when you *had* to say "2052" in your RIF, or some IBM TCP/IP implementations wouldn't talk to you at all. Thus, you are likely to find that as a widely-used default... James B. VanBokkelen 26 Princess St., Wakefield, MA 01880 FTP Software Inc. voice: (617) 246-0900 fax: (617) 246-0901