Path: utzoo!utgpu!watmath!clyde!att!pacbell!ames!haven!decuac!hadron!jsdy From: jsdy@hadron.UUCP (Joseph S. D. Yao) Newsgroups: comp.protocols.tcp-ip Subject: Re: Uniq <=> Ultrix Summary: Thanks for the help ... Message-ID: <829@hadron.UUCP> Date: 11 Jan 89 08:04:04 GMT References: <828@hadron.UUCP> Reply-To: jsdy@hadron.UUCP (Joseph S. D. Yao) Organization: Hadron, Inc., Fairfax, VA Lines: 47 In article <828@hadron.UUCP> I (Joseph S. D. Yao) write: >... >Instrumentation of the Uniq side shows that the TCP level is receiving >several packets perfectly reasonably, then all of a sudden getting a >packet whose sequence number is 1024 more than expected! ... Many thanks to the several people who immediately suggested an answer that seems to exactly fit the problem: Ed Frankenberry Doug Nelson <08071TCP%MSU.BITNET@CUNYVM.CUNY.EDU> cpw%sneezy@LANL.GOV (C. Philip Wood) map@gaak.LCS.MIT.EDU (Michael A. Patton) "Mark D. Eggers (219) 239-7258" Mike Muuss Apparently, as I'd suspected, Ultrix 2.2 TCP/IP is 4.3BSD-alpha. It offers "trailers" by default. If a large packet is sent, 1024 bytes are sent in a "trailer", which the Uniq (4.1BSD) TCP or IP (I think the latter) doesn't recognize ... hence my symptom of suddenly finding sequence numbers boosted by 1024. The universally proffered solution was to put "-trailers" as an argument to 'ifconfig' in the system initialisation file "/etc/rc.local". It was suggested that the Ultrix implementation of trailers, being 4.3-alpha, might be incomplete; or that Uniq TCP/IP, being older, probably doesn't understand trailers. This is not surprising. I'd already changed the net broadcast address to all-zeroes, since the Uniq implementation of all-ones is incomplete. I'll try this tomorrow. If you don't hear from me again on this, this is the final answer. Mike Muuss, as always, thinks up more possibilities. I don't under- stand his second suggestion, so I'll include it verbatim and let him elucidate, if he wants. > 2) check the offered TCP MSS -vs- what is getting sent. He also adds: > A Sun running "TCPDUMP", or an ethernet analyzer, will be helpful. Joe Yao jsdy@hadron.COM (not yet domainised) hadron!jsdy@{uunet.UU.NET,dtix.ARPA,decuac.DEC.COM} arinc,att,avatar,blkcat,cos,decuac,dtix,\ ecogong,empire,gong,grebyn,inco,insight, \!hadron!jsdy kcwc,lepton,netex,netxcom,phw5,rlgvax, / seismo,sms,smsdpg,sundc,uunet /