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Newsgroups: news.answers,bit.listserv.big-lan,comp.dcom.lans.misc From: jmwobus@mailbox.syr.edu (John Wobus) Subject: BIG-LAN/bit.listserv.big-lan FAQ Message-ID: <1993Nov4.080300.18809@newstand.syr.edu> Date: Thu, 4 Nov 93 08:02:59 EST Approved: jmwobus@mailbox.syr.edu Archive-name: LANs/big-lan-faq BIG-LAN Frequently Asked Questions Last Updated: April 18, 1993 Acknowledgements: A lot of people provided information for me and I freely admit that I have not recorded the list of names. Thanks to all. Contents -------- I. About BIG-LAN II. Explanation of this Memo III. Sources of Information on Campus Networks 1. Must-Read Sources 2. A Few General Sources 3. LISTSERV Mailing Lists 4. Internet Mailing Lists 5. Internet Mailing Lists with automatic subscription 6. USENET/Netnews Groups 7. Anonymous FTP-based Archive Sites 8. LISTSERV-based Archive Sites 9. RFCs (Internet "Request For Comments") 10. Other Useful Online Papers 11. Sources of Protocol Documents 12. Useful Free Software 13. Books 14. Periodicals 15. Training Courses 16. Conferences IV. Basic Glossary on Campus Networks V. Frequently Asked Questions on Campus Networks 1. What is the difference between Ethernet and IEEE 802.3? 2. What is encapsulation? What do I have to know about it? 3. How do I know whether to use a router or a bridge? 4. How do I know whether to use a bridge or a repeater? How many repeaters may I put on an Ethernet? 5. Should I use "manageable" hubs, concentrators, etc on my LAN? 6. Which LAN technology should I use? Arcnet? FDDI? Token Ring? 10BASE-T? 7. What is the ideal cable to install in a new building? 8. What is the ideal cable to install between buildings on a campus? 9. Whose routers are recommended? 10. Whose bridges are recommended? 11. Whose Ethernet equipment are recommended? 12. Whose Token Ring equipment are recommended? 13. Whose FDDI equipment are recommended? 14. What PC network software is recommended? 15. What protocols should run on a campus-wide LAN? 16. What software is recommended for managing a campus-wide LAN? 17. What terminal server is recommended? 18. Whose troubleshooting equipment are recommended? 19. What security products should I buy? 20. Should the names of devices on my campus LAN have subdomains? 21. Should client stations use POP? Should they use just SMTP? Should I use some non-TCP/IP protocol for mail to/from client stations? 22. Should I enable SQE/heartbeat? I. About BIG-LAN BIG-LAN is a mailing list for discussion of issues in designing and operating Campus-Size Local Area Networks, especially complex nes utilizing multiple technologies and supporting multiple protocols. Topics include repeaters, bridges, routers and gateways; how to incorporate smaller Personal-Computer type LANs into the campus-wide LAN; how to unify the mail systems, etc. This is an ideal list in which to debate the relative merits of bridges vs routers. All requests to be added to or deleted from this list, problems, questions, etc., should be sent to BIG-LAN-REQUEST@SUVM.ACS.SYR.EDU (Internet) or BIG-REQ@SUVM (Bitnet). Those familiar with LISTSERV can subscribe with LISTSERV@SUVM.ACS.SYR.EDU (Internet) or LISTSERV@SUVM (Bitnet). Archives are available through LISTSERV and anonymous ftp. Coordinator: John Wobus <JMWOBUS@SYR.EDU> <JMWOBUS@SUVM> II. Explanation of this Memo Since BIG-LAN is not specific to any protocol family, it will not cover any particular protocol family in detail, e.g. this is not a TCP/IP/Internet FAQ Memo. Fortunately, there are some good TCP/IP FAQ Memos which are listed in the sources of information below. Suggestions, corrections, and contributions welcome. Please send them to: big-lan-request@suvm.acs.syr.edu BIG-REQ@SUVM.BITNET III. Sources of Information on Campus Networks This list favors "network" sources of information: available on the Internet and/or BITNET and other similar networks; if you have access to BIG-LAN then you have access to one of these networks; and these sources are not the kind which you can discover through vendors, books, bookstores, or libraries. 1. Must-Read Sources These are documents that you definitely should get and read if you have questions about Campus Networks. a. Charles Spurgeon's reading list (see below under "Other Useful Online Papers"). b. RFCs 1175, 1325, 1207, and 1392 (see below under "RFCs"). 2. A Few General Sources These are network resources & mechanisms for getting all kinds of information--not just on Networking; thus we can't cover them very thoroughly in this memo. a. LISTSERV - mailing list servers & file servers on BITNET, accessible via e-mail. Can be reached and used from a lot of networks. Mail the command INFO to any LISTSERV for help. Also have database commands (i.e. search commands) for archives they store. b. Usenet News/Netnews: distributed bulletin board with discussions on lots of topics. Distributed through the Internet and through UUCP. c. Anonymous ftp: the main way to make files available on the Internet. ftp to a site using username "anonymous". A password is always demanded--sometimes a banner tells you what to use--otherwise "guest" almost always works. d. Archie servers - network-accessible databases of where to get files via anonymous ftp. Access is through telnet, rlogin, mail, or a special "archie" protocol. To use via telnet, enter username archie. Some servers: archie.ans.net, archie.sura.net, archie.mcgill.edu, archie.unl.edu. e. WAIS - Internet-accessible databases on different topics. Available via WAIS protocol (basically Z39.50). Client (and server) software is collected on quake.think.com as well as a WAIS database of WAIS servers. f. ftplist.txt - collected list of anonymous ftp sites. Stored lots of places in anonymous ftp including syr.edu. g. Internet gopher - something like anonymous ftp only more advanced: to get started, I suggest ftping boombox.micro.umn.edu and getting information on gopher. A number of sites have servers. h. Internet List of lists: available by anonymous ftp from ftp.nisc.sri.com, or through a mail-based file server at mailserver@nisc.sri.com. i. LISTSERV internal list of lists. Available by mailing the command LIST GLOBAL to any LISTSERV. j. news.answers - newsgroup that distributes Frequently Asked Questions memos for lots of Netnews groups. k. FAQ archive available via anonymous ftp on pit-manager.mit.edu From the archives of news.answers, Frequently Asked Question memos for lots of Netnews groups. l. news.announce.newusers - has periodic postings about how to use Usenet/Netnews and also a lot about mailing lists. m. BITFTP. A BITNET server that allows BITNET sites to use the Internet's File Transfer Protocol to send/receive files to ftpable Internet sites. For more information, send mail to BITFTP@PUCC with HELP as the message body. n. Database of lists managed by LISTSERV@VM1.NODAK.EDU. Use through LISTSERV's database interface. o. Maas files--Indexes & abstracts about various services available via Internet & BITNET including some related to campus networks. Available via anonymous ftp from ftp.unt.edu. p. NETSCOUT@VMTECMEX.BITNET mailing list. A list to exchange information on the location of network resources. LISTSERV-based so use instructions below to subscribe, etc. 3. LISTSERV Mailing Lists Send a "SUBSCRIBE" command to LISTSERV@foo, e.g. SUBSCRIBE BIG-LAN John Doe a. BIG-LAN@SUVM.BITNET/SUVM.ACS.SYR.EDU b. NOVELL@SUVM.BITNET/SUVM.ACS.SYR.EDU c. CDROMLAN@IDBSU.BITNET/IDBSU.IDBSU.EDU d. BANYAN-L@AKRONVM.BITNET e. CW-EMAIL@TECMTYVM.BITNET (Campus Wide E-mail) f. CWIS-L@WUVMD.BITNET (Campus Wide Information Systems) g. IBM-NETS@BITNIC.BITNET h. LWUSERS@NDSUVM1.BITNET (LANWatch User List) i. TN3270-L@RUTVM1.BITNET j. 3COM-L@NUSVM.BITNET h. HELP-NET@TEMPLEVM.BITNET (Help re networking software) i. LANWORKS@MIAMIU.BITNET (LanWorks PCSA stuff) j. LANMAN-L@NIHLIST.BITNET (MS LAN MAN stuff) 4. Internet Mailing Lists Send a subscription request for list foo to foo-request@blah a. big-lan@suvm.acs.syr.edu (gives you 2 ways) b. cisco@spot.colorado.edu c. p4200@comet.cit.cornell.edu (Proteon routers) d. tcp-ip@nic.ddn.mil e. netblazer-users@telebit.com f. info-appletalk@andrew.cmu.edu g. net-ops@nsl.dec.com h. nfs@tmc.edu i. wellfleet-l@nstn.ns.ca j. ospf@trantor.umd.edu (OSPF IP routing protocol) k. pop@jhunix.hcf.jhu.edu l. bind@ucbarpa.berkeley.edu m. pc-ip@udel.edu n. drivers@sun.soe.clarkson.edu (Packet Drivers) o. cell-relay@indiana.edu gatewayed to comp.dcom.cell-relay) 5. Internet Mailing Lists with automatic subscription Send a "SUBSCRIBE" command to the listed server. a. firewalls@greatcircle.com majordomo@greatcircle.com (about firewall routers) b. firewalls-digest@greatcircle.com majordomo@greatcircle.com (same list in digested form) 6. USENET/Netnews Groups a. comp.dcom.* lans, modems, sys.cisco, telecom, ... b. comp.protocols.* appletalk, tcp-ip, ibm, ppp, ... c. comp.sys.proteon d. comp.sys.novell e. comp.sys.mac.comm f. bit.listserv.big-lan (Note: these groups give Netnews g. bit.listserv.novell readers a way to read the corresponding h. bit.listserv.cwis-l LISTSERV lists) i. bit.listserv.cw-mail j. bit.listserv.3com-l k. alt.dcom.* catv, telecom, ... 7. Anonymous FTP-based Archive Sites a. syr.edu: BIG-LAN mailing list; NOVELL mailing list; a collection of network-oriented papers. b. spot.colorado.edu: cisco mailing list & some other network stuff c. hsdndev.harvard.edu: (in ndtl/results) Results of Scott Bradner's router benchmarks. d. ftp.uu.net: a treasure trove of software. e. wuarchive.wustl.edu: a treasure trove of software. f. vax.ftp.com: packet drivers, some Unix software, other stuff. g. ftp.utexas.edu: collection of networking info & software. h. ftp.slc.is.novell.com: files Novell makes available. i. ftp.cisco.com: files Cisco makes available & some interesting applications. j. gatekeeper.dec.com: a treasure trove of software & stuff (the stuff that was on decwrl.dec.com). k. lux.levels.unisa.edu.au: files that 3Com distributes via Compuserve. l. ftp.unt.edu: Maas files and other goodies. m. simtel20.army.mil: a treasure trove of software, including packet drivers (pd1:<msdos.pktdrvr>). Mirrored on ftp.uu.net and wuarchive.wustl.edu. n. osi.ncsl.nist.gov: online copies of GOSIP & related documents. 8. LISTSERV-based Archive Sites The brave can mail the command "INFO FILES" and/or the command "INFO DATABASE" to the LISTSERV for instructions. a. LISTSERV@SUVM.BITNET: BIG-LAN & NOVELL mailing list archives. 9. RFCs (Internet "Request For Comments") Some anonymous ftp sites for RFCs: nic.ddn.mil, ftp.nisc.sri.com, nis.nsf.net, nisc.jvnc.net, venera.isi.edu, wuarchive.wustl.edu. There are also some mail-based file servers: mailserver@nisc.sri.com, info-server@nnsc.nsf.net, and sendrfc@jvnc.net. a. RFC1147: FYI on a network management tool catalog: Tools for monitoring and debugging TCP/IP internets and interconnected devices b. RFC1175: FYI on where to start: A bibliography of internetworking information c. RFC1325: FYI on Questions and Answers: Answers to commonly asked "new Internet user" questions d. RFC1178: Choosing a name for your computer e. RFC1207: FYI on Questions and Answers: Answers to commonly asked "experienced Internet user" questions f. RFC1244: Site Security Handbook g. RFC1118: Hitchhiker's Guide to the Internet h. RFC1122 & RFC1123: Requirements for Internet Hosts i. RFC1208: A Glossary of Networking Terms j. RFC1180: A TCP/IP Tutorial k. RFC1173: Responsibilities of Host and Network Managers: A Summary of the Oral Tradition of the Internet l. IAB Official Protocol Standards (Currently RFC1360 but it is periodically updated & given a new RFC number) m. Assigned Numbers (Currently RFC1340 but it is periodically updated & given a new RFC number; Includes field-values for protocols in the TCP/IP family as well as some others) n. RFC1392: Internet User's Glossary 10. Other Useful Online Papers a. Charles Spurgeon. "Network Reading List: TCP/IP, UNIX, and Ethernet". Available via anonymous ftp from ftp.utexas.edu in directory pub/netinfo/docs as net-read.txt and netread-ps. Also available via electronic-mail-based archive server. Send the word "help" in the subject header or body of a message to archive-server@ftp.utexas.edu for more information. b. Charles Hedrick. "Introduction to the Administration of an Internet-based Local Network". Available via anonymous ftp from cs.rutgers.edu as runet/tcp-ip-admin.doc (also .ps). c. Charles Hedrick. "Introduction to Internet Protocols." Available via anonymous ftp from cs.rutgers.edu as runet/tcp-ip-intro.doc (also .ps). d. Unofficial lists of codes used on 802.3 & Ethernet networks. Portions of the official list are not released, so various people compile unofficial lists. One that is available via anonymous ftp is Michael Patton's pub/map/EtherNet-Codes on ftp.lcs.mit.edu. See also RFC: "Assigned Numbers". e. Scott Jenkins: "Frequently Asked Questions for NOVELL@SUVM Mailing List." Available via anonymous ftp from info.umd.edu in the info/Computers/Novell/Information directory. f. Brendan Kehoe: "Zen and the Art of the Internet: A Beginner's Guide to the Internet." Available via anonymous ftp from ftp.cs.widener.edu in the pub/zen directory. g. ATM Bibliography. Available via anonymosu ftp from mythos.ucs.indiana.edu. 11. Sources of Protocol Documents a. Ethernet V2 DEC-Direct; 1-800-344-4825; DEC Part Number AA-K759B-TK. b. IEEE 802 (802.3, Token Ring, 10BASE-T, etc) IEEE; 1-800-678-IEEE. c. TCP/IP RFCs. See RFCs (above). d. Appletalk APDA; 1-800-282-APDA. Now a book in the "Inside" series. e. OSI Omnicom Inc.; 1-800-666-4266. f. DECNet DEC. g. SNA IBM. h. Novell(IPX) Built on XNS; rest is designed by Novell. i. FDDI ANSI; 1-212-642-4900. Also Global Engineering Documents; 1-800-854-7179. 2805 McGaw Avenue; PO Box 19539; Irvine, CA 92714; 1-714-261-1455. j. CCITT United Nations book shop in New York Also there is a new online service mail-based document server available from ITU called teledoc@itu.arch.ch. k. GOSIP NTIS Sales Dept; (703)487-4650; Document FIPS 146-1; See also Anonymous FTP-based Archive Sites l. XNS Xerox. 12. Useful Free Software (see also RFC1147; listed above) a. CUTCP (TCP/IP client for PCs) sun.soe.clarkson.edu, omnigate.clarkson.edu b. NCSA Telnet (Telnet clients for PCs & Macs) ftp.nsca.uiuc.edu c. Eudora (POP3 Client for Macs) ux1.cso.uiuc.edu d. POPmail (POP3 Client for PCs & Macs) boombox.micro.umn.edu e. PCROUTE (Makes IP router out of PC) accuvax.nwu.edu f. PCBRIDGE (Makes bridge out of PC) accuvax.nwu.edu g. Packet Drivers (Drivers for various PC LAN cards) simtel20.army.mil h. WinQVT (IP clients for Windows) ftp.cica.indiana.edu i. ka9q (TCP/IP for PCs and Macs) ucsd.edu j. PC/IP (TCP/IP client for MS-DOS) husc6.harvard.edu k. charon (Pegasus/smtp gateway) omnigate.clarkson.edu l. CAP (AppleTalk for Unix systems) rutgers.edu, munnari.oz.au, gatekeeper.dec.com m. Popper (POP3 server for Unix systems) ftp.cc.berkeley.edu n. Trumpet (PC Newsreader) simtel20.army.mil o. bootpd (Bootp Daemon for Unix) lancaster.andrew.cmu.edu p. NUPOP (POP3 daemon for MS-DOS) ftp.acns.nwu.edu q. PC netwatching program [I don't know name or site] r. iupop3 (POP3 server for VMS) mythos.ucs.indiana.edu 13. Books The following books were mentioned by responders to the 12/91 BIG-LAN Reader Survey as good books for administrators of Campus-sized LANs: a. Douglas Comer. Internetworking with TCP/IP. b. Marshall Rose. The Simple Book. c. Caroline Arms. Campus Networking Strategies. Digital Press. Out of print. d. DEC Telecomm. & Network Buyer's Guide. f. Marshall Rose. The Open Book. g. Carl Malamud. Analyzing Novell Networks. h. Andrew Tanenbaum. Computer Networks. i. Martin A. W. Nemzow. Keeping The Link (McGraw-Hill). j. William Stallings. Local Networks: an Introduction. k. John McCann. NetWare Supervisor's Guide. l. William Stallings. Handbook of Communications Standards. (?) m. Nemeth, Snyder & Seebass. Unix System Administration Handbook. Other interesting looking books: n. Mark A. Miller. Troubleshooting Internetworks. 14. Periodicals The following periodicals were mentioned by responders to the 12/91 BIG-LAN Reader Survey as good periodicals for administrators of Campus- sized LANs: a. LAN Times b. Communications Week c. Network Computing d. ConneXions e. Data Communications f. Network World g. LAN Magazine h. Info World i. SunExpert j. Telecommunications k. Computerworld l. DataCommunicationInternational m. Datamation n. Digital Review o. LAN Technology p. Lightwave q. MacUser r. MacWeek s. MacWorld t. Networking Management u. PC Week 15. Training Courses The following providers of tutorials were mentioned by responders to the 12/91 BIG-LAN Reader Survey: a. Interop b. ACM SIGComm c. Learning Tree d. Novell e. PSI f. Usenix 16. Conferences The following conferences were mentioned by responders to the 12/91 BIG-LAN Reader Survey as good conferences for administrators of Campus- sized LANs: a. Interop b. Usenix c. ComNet d. NetWorld e. ACM SIGComm f. DECUS g. IETF IV. Basic Glossary on Campus Networks Another glossary is RFC1208. See "Online Papers" above. ANSI "American National Standards Institute" - A definer of standards of all kinds, including FDDI. Appletalk - A protocol family developed by Apple Computer to implement LANs serving Macintoshes. ATM "Asynchronous Transfer Mode" - a method for switching little fixed-size packets (cells) around. Like T1 and DS3, digitized voice was a major consideration in its design, but it can be used for data. It is designed around fixed speeds too, roughly 150MBS and 600MBS. The fixed cell size is 53 bytes. Though ATM is really designed for voice and WANs, there are schemes to use it in LANs. ATM is a big buzzword these days but it is still very new. AUI "Attachment Unit Interface" - the Ethernet/IEEE 802.3 term for the interface between a MAU and a station. A special kind of cable known as an "AUI Cable" can attach a MAU to a station at a distance (up to 50 meters). BNC Connector "Bayonet Neill-Concelman connector" - a type of connector used for attaching coax cable to electronic equipment which can be attached or detached quicker than connectors that screw. ThinWire Ethernet (IEEE 802.3 10BASE2) uses BNC connectors. Bridge - A network "relay" which reads, buffers, and sends data to relay it from one data link to another, but makes the two data links appear as one to levels higher than the data link layer. CDDI "Copper Data Distribution Interface" - essentially a way to use electrical communications cables in an FDDI network. Several companies have worked out ways to do this but ANSI has yet to standardize one. I think CDDI was coined by Crescendo corporation for their scheme, but it may well be adopted by ANSI as the name. So far there are schemes that work on Coax, on STP and UTP, but the front runners look like they will be able to run on UTP for about 100 meters. CMIP "Common Management Information Protocol" - An OSI protocol for management of network equipment. Not widely implmented. See SNMP. CMOT "CMIP over TCP/IP" - A protocol consisting of CMIP running under TCP/IP. An alternative to SNMP. Coaxial Cable - any of a number of kinds of electrical communications cable designed so one conductor is in the center and the second conductor forms a ring around it. Depending upon who you talk to, someone might have a specific kind of coaxial cable in mind. Some well known kinds are various Cable TV cables, cables used by IBM 327x terminals and ARCnet, and cables used by Ethernet & IEEE 802.3. DECnet - Trade name of Digital Equipment Corporation for some of their networking products. It is a kind of network built out of Digital Equipment Corporations own networking protocols (with some standard protocols also used). Dialup Modem - Modem used over ordinary dial-up telephone lines as opposed to private or leased lines. Ethernet - LAN data-link protocol developed by a consortium of vendors; later standardized as IEEE 802.3 with a few modifications. For many applications, users have not adopted all the IEEE 802.3 differences. Ethernet/802.3 now can be run on two types of coaxial cable as well as multi-mode fiber and unshielded twisted-pair. "Raw" rate of data transmission is 10 megabits/second. FDDI "Fiber Data Distribution Interface" - LAN data-link protocol. Designed to run on multi-mode fiber. "Raw" rate of data transmission is 100 megabits/second. Developed by the American National Standards Institute. FDDI-2 - Same speed, same fiber, same basic protocol as FDDI. FDDI-2 adds a layer which allows you to allocate fixed bandwith to applications of your choice, making it more like broadband. FDDI-2 is still rather new. Fiber - optical fiber: a very long, narrow, flexible piece of glass. Used for high-speed communications. Firewall Router - a router which blocks traffic according to various criteria for security--for example a router which allows no telnet to any host through one of its interfaces but allows ftp to a list of authorized hosts through the same interface. FOIRL "Fiber Optic Inter-Repeater Link" - a standard for running IEEE 802.3 over fiber. It was originally designed to link two repeaters, and only supports two attachments. Many users use it to attach a station to a repeater. See 10BASE-F. FTP - Protocol in the "TCP/IP" family for copying files from one computer to another. Stands for "File Transfer Protocol". Gateway - A type of "network relay" that attaches two networks to build a larger network. Modern "narrow" usage is that it is one that translates an entire stack of protocols, e.g., translates TCP/IP-style mail to ISO-style mail. Older usage used it for other types of relays--in particular, in the "TCP/IP" world, it has been used to refer to what many now insist is a "router". GOSIP "Government Open Systems Interconnect Profile" - A subset of OSI standards specific to US Government procurements, designed to maximize interoperability in areas where plain OSI standards are ambiguous or allow options. Theoretically, required of all US Government networking procurements since mid-1990. Heartbeat - In Ethernet (Version 2), a test of the collision functionality of the transciever. The term "Heartbeat" is often (wrongly) used interchangeably with "SQE" which is a similar function of IEEE 802.3. See Question on SQE/Heartbeat below. IPX - Novell's protocol used by Netware. Utilizes part of XNS. A router with "IPX routing" purports to interconnect LANs so that Novell Netware clients & servers can talk through the router. MAU "Media Adaptor Unit" - an IEEE 802.3 or Ethernet device which attaches a station to the cable. Popularly called a "transceiver". Can be attached by cable to the station or built into the station. MIB "Management Information Base" - the set of parameters an SNMP management station can query or set in an SNMP agent (e.g. router). Standard, minimal MIBs have been defined (MIB I, MIB II), and vendors often have custom entries. In theory, any SNMP manager can talk to any SNMP agent with a properly defined MIB. Multimode fiber - A type of fiber mostly used for shorter, e.g. campus distances. It can carry 100 megabits/second for typical campus distances, the actual maximum speed (given the right electronics) depending upon the actual distance. It is easier to connect to than Single Mode Fiber, but its limit on speed x distance is lower. NFS "Network File System" - an IP-based protocol originally developed by Sun Microsystems which provides file services. OSI "Open System Interconnect" - A standard put forth by the ISO for communication between computer equipment and networks. OSI Reference Model - A model put forth by the ISO for communication between computer equipment and networks, which maps out 7 protocol layers. Top layer: layer number 7: application layer layer number 6: presentation layer layer number 5: session layer layer number 4: transport layer layer number 3: network layer layer number 2: data-link layer (e.g. IEEE 802.x) Bottom layer: layer number 1: physical layer (wire & electricity) This model explains what each layer does. The model is often used to explain anyones protocols (not just OSI) to the point where many people seem to believe that true data-communications requires these 7 layers. POP "Post Office Protocol" - A TCP/IP-based protocol designed to allow client-stations (e.g. micros) to read mail from a server. There are three versions under the name "POP": POP, POP2, and POP3. Latter versions are NOT compatible with earlier versions. Protocol - The "rules" by which two network elements trade information in order to communicate. Must include rules about a lot of mundane detail as well as rules about how to recover from a lot of unusual communication problems. Thus they can be quite complicated. Relay - One terminology uses the term "relay" as a device that interconnects LANs, different kinds of relays being repeaters, bridges, routers, and gateways. Repeater - In the "Ethernet" world, a "relay" that regenerates and cleans up signals, but does no buffering of data packets. It can extend an Ethernet by strengthening signals, but timing limitations on Ethernets still limit their size. RFC "Request For Comments" - The name is a real red herring when it comes to Internet RFCs. Some really are "Requests For Comments" but all Internet protocol documents are stamped with an RFC number that they never shake, so the acronym RFC generally refers to documents that describe protocols in the TCP/IP family. RG numbers (E.g. RG62; sometimes there are qualifiers, e.g. RG 58 A/U) a shorthand designation for military cable. RG58 & RG62 designate two different types of cable used by the military. Some data-communications equipment was designed to work with a particular military standard, e.g. IBM 3270-type terminals use RG62. In other cases, people use an RG-numbered cable that is close to what they need: for example Thinwire Ethernet & IEEE 802.3 10BASE2 define the type of cable they need and people sometimes substitute flavors of RG58, which are "close". One can't recommend this practice because you can get yourself in trouble. I think "RG" originally stood for "Radio Guide", presumably reflecting the fact that the series of cables was designed to handle radio frequencies. The IEEE 802.3 10BASE2 specifications define two RG numbered cables (RG58 A/U and RG58 C/U) as meeting the cable requirements for thin Ethernet. However, cable vendors may list a range of cables under these same RG numbers, and some of the cables listed may not meet the 802.3 specs. You need to check the cable specifications closely, and beware of relying on the RG number alone when ordering network cables. Router - A network "relay" that uses a protocol beyond the data-link protocol to route traffic between LANs and other network links. Routing Protocol - a protocol sent between routers by which routers exchange information own how to route to various parts of the network. The TCP/IP family of protocols has a bunch, such as RIP, EGP, BGP, OSPF, and dual IS-IS. Shielded Twisted Pair - a type of twisted-pair cable with a metallic shield around the twisted conductors. The shield reduces the noise from the cable and reduces the effects of noise on the communications in the cable, but changes the electrical characteristics of the cable so some equipment optimized to non-shielded cable runs worse on shielded cable. Single Mode fiber - a type of fiber optic cable used for longer distances and higher speeds, e.g. for long-distance telephone lines. See also "Multimode Fiber". SMTP "Simple Mail Transfer Protocol" - the protocol in the TCP/IP family used to transfer electronic mail between computers. It is not oriented towards a client/server system so other protocols (see "POP") are often used in that context. However, servers will use SMTP if they need to transfer a message to another server. SNMP "Simple Network Management Protocol" - Originally developed to manage IP based network equipment like routers and bridges, now extended to wiring hubs, workstations, toasters, jukeboxes, etc. SNMP for IPX and AppleTalk under development. Widely implemented. See CMIP. SQE Test "Signal Quality Error Test" - an IEEE 802.3 function that tests the transceiver. The term "SQE" is often (wrongly) used interchangeably with "Heartbeat" which is a similar function of Ethernet Version 2. See Question on SQE/Heartbeat below. TCP/IP "Transmission Control Protocol/Internet Protocol" - literally, two protocols developed for the Defense Data Network to allow their ARPANET to attach to other networks relatively transparently. The name also designates the entire family of protocols built out of IP and TCP. The Internet is based upon TCP/IP. TELNET - a protocol in the TCP/IP family that is used for "remote login". The name is also often used as the name of the client program that utilizes the TELNET protocol. Terminal Server - a network device that allows a number of terminals to attach to a LAN, and do remote logins across the LAN. TN3270 - A variant of the TELNET program that allows one to attach to IBM mainframes and use the mainframe as if you had a 3270 or similar terminal. Token Ring - People often mean 802.5 when they say "Token Ring" (see below). In the more general sense of the word, a type of LAN that has stations wired in a ring, where each station constantly passes a special message (a "token") on to the next. Whoever has the token can send a message. Tunnelling - An important concept in the design of many kinds of networks: taking some protocol-family's ability to move packets from user to user, or to open virtual-circuits between users, and use this as if it were a data-link protocol to run another protocol family's upper layers (or even the same protocol family's upper layers). Examples: running TCP/IP over Appletalk instead of something like Ethernet; running Appletalk over DECnet instead of something like Localtalk or Ethernet. Twisted Pair - The type of wire used by the phone company to wire telephones -- at least over distances like between your house and the central office. It has two conductors, which are twisted. The twists are important: they give it electrical characteristics which allow some kinds of communications otherwise not possible. Ordinary telephone cables are not shielded (see "Shielded twisted Pair"). T1 - A phone-company standard for running 24 digitized voice circuits through one 1.5megabit/second digital channel. Since phone companies run lots of T1, and will run T1 between customer sites, the standard is often used for data communications, either to provide 24 low-speed circuits, or to provide 1 high-speed circuit, or to be divided other ways. UTP (Unshielded Twisted-Pair) - See "Twisted-Pair" and "Shielded Twisted-Pair". X.400, X.500 - OSI protocols for mail and directory services. 10BASE-T - A variant of IEEE 802.3 which allows stations to be attached via twisted-pair cable. 10BASE-F - A variant of IEEE 802.3 under development which allows stations to be attached via multimode fiber. It will offer a variety of methods of using fiber in an IEEE 802.3 network that go beyond what is currently offered in FOIRL. The current 10BASE-F draft is likely to be confirmed. Sections of the draft include "Fiber Optic Medium and Common Elements of Medium Attachment Units and Star, Type 10BASE-F (Section 15)", "Fiber Optic Passive Star and Medium Attachment Unit, Type 10BASE-FP (Section 16)", "Fiber Optic Medium Attachment Unit, Type 10BASE-FB (Section 17)", and "Fiber Optic Medium Attachment Unit, Type 10BASE-FL (Section 18)". 802 - The set of IEEE standards for the definition of LAN protocols. A story goes that a long time ago, IEEE and ANSI decided that IEEE would get the slow protocols and ANSI would get the fast ones, thus IEEE defined the 802 protocols and ANSI defined FDDI. Presumably IEEE saw limited application for FDDI at the time. Also, the IEEE standards-making committees associated with these standards. 802.1 - The IEEE 802 standard for Network Management and Network Bridging of IEEE 802 networks. 802.2 - An IEEE standard for the portion of LAN data-link protocols that is the same for all flavors of IEEE LAN protocols, e.g. 802.3 and 802.5. Sometimes not used. 802.3 - An IEEE standard for LANs--their "improved" version of Ethernet. See Ethernet. 802.4 - An IEEE standard for LANs: Token Bus networks. Basically, standardizes MAP, a protocol that operates a Token Bus protocol on broadband. 802.5 - An IEEE standard for Token-Ring-based LANs. See Token Ring. 802.6 - An IEEE standard for Metropolitan Area Networks. Also known as DQDB. 802.7 - IEEE 802 technical advisory group on Broadband. 802.8 - IEEE 802 technical advisory group on FDDI & fiber optics. 802.9 - IEEE 802 group on integrated data & voice networks. 802.11 - Proposed IEEE 802 group for wireless Ethernet. V. Frequently Asked Questions on Campus Networks It is hard to answer typical BIG-LAN questions in advance for two reasons. Answers are often long and they are often controversial. To provide some sort of objective information relevant to the controversies, a survey of BIG-LAN readers was taken on answers to various questions, so this memo could offer a sampling of opinions. Note that the opinions below are extracted from the 41 responses received for the survey. We can't say these 41 responses represent a fair sampling of campus LAN administrators, but they do show some of the answers that you would get if you posed some of these questions to the BIG-LAN readership. 1. What is the difference between Ethernet and IEEE 802.3? Ethernet ran through an evolution starting with some experimenting at Xerox, and ending with a standard published by Xerox, DEC, and Intel, which they offered to the world (with minimal royalties) as a standard technology for building LANs. The Institute of Electrical & Electronic Engineers took this as a proposed standard, and rewrote the protocol description making some clarifications and a few changes. Some of the changes have been universally adopted, and others have not. After the first go round of IEEE standard defining, Ethernet version 2 was introduced which brought it more into line with standards. The basic differences are: - Heartbeat vs SQE (see below) - Which pin in the MAU & AUI connectors carry the ground conductor - Packet Length Field vs Type Field The latter issue is the one in which IEEE 802.3 has not displaced Ethernet. Ethernet had a 16-bit field which defined the type of packet (examples: IP, XNS, Appletalk). The IEEE committee decided to use that field to specify the length of the packet, and have the data-portion of the packet define itself through the next higher level of protocol (e.g., IEEE 802.2). However, the sets of possible values for that field used by the two different protocols are completely separate, and both protocols are designed to deliberately ignore packets with fields outside their own sets of values. Thus Ethernet and IEEE 802.3 packets can coexist on the same cable, though a computer which expects to get packets belonging to just one of the protocols won't notice any packets sent according to the rules of the other (the expression used is "they pass by each other like ships in the night"). These days, LANs use both. There is a way to send TCP/IP packets via 802.3, but when 802.3 was introduced, there were already so many systems using the Ethernet rules that the use of Ethernet-style packets for TCP/IP has persisted now for years. 2. What is encapsulation? What do I have to know about it? One encapsulation issue on LANs is whether IEEE 802.3 packets are used or Ethernet packets are used to encapsulate your traffic on your IEEE 802.3/Ethernet LAN. See previous question for more explanation. Most TCP/IP systems use Ethernet, any that uses IEEE 802.3 by default might surprise you by not interoperating with the rest of your TCP/IP network. A second encapsulation issue on IEEE 802.3/Ethernet networks is whether your Novell (IPX) packets use Novell's default encapsulation or whether they use Ethernet-style encapsulation. Novell, at least for a long time, had the distinction of using IEEE 802.3 as if it were the only protocol on the network, not following the rules for avoiding other protocols running under IEEE 802.3 rules. They offered a utility called ECONFIG that changed Netware to use Ethernet rules, and use them properly, so Novell IPX packets could utilize the same LAN as other protocols. In no case would the Novell traffic bother Ethernet traffic-- only any other IEEE 802.3 traffic if ECONFIG wasn't used. In any case, a single Ethernet segment, or bridged segments, had to have all Novell servers and clients configured the same, in order to interoperate. A third encapsulation issue stems from Berkeley Unix 4.2, from which many versions of Unix and many TCP/IP implementations have been modeled. It used, by default, its own encapsulation rules (i.e., manner of putting IP packets within Ethernet packets) which is termed "Trailer Encapsulation". When an Ethernet had some computers using Trailer Encapsulation and some not, TCP/IP connections would often work, but hang when large data transfers were taking place. The next version of Berkeley Unix, version 4.3, remedied this by avoiding Trailer Encapsulation except when it was guaranteed to work correctly. A fourth encapsulation issue is "tunnelling", which consists of one of the layers in the protocol stack mimicking another layer to provide a way of running a different set of upper layers than would otherwise be possible. This is rather widely used and seldom explained to beginners. It is perhaps best explained with an actual example: [Here put an example, perhaps Appletalk over IP] [Include "encapsulated bridging" as a second example] 3. How do I know whether to use a router or a bridge? (Note that the answer to this question is oriented to Ethernet-based LANs). Few administrators of networks doubt that a network can be large enough to require routers nor that there are situations where a bridge is an effective solution. However, there is controversy as to where to draw the line. Campus-sized networks involving distances of up to a mile and possibly thousands of stations, can be, and have been built solely out of one or the other. The BIG-LAN Survey of 12/91 showed the following opinion among respondents: Survey question: "When you build a campus network, do you tend to use bridges as opposed to routers?" Answers: 9 said yes; 26 said no; 2 said "brouters" (combination bridge/routers) would be the best solution. Some clear tradeoffs: routers generally have to be set up no matter what whereas bridges can be plug-and-play on a network without too much total traffic; bridges generally have a higher speed-to-cost ratio and the low-end bridge is less expensive than the low-end router; routers handle huge networks with links of different speeds better. 4. How do I know whether to use a bridge or a repeater? How many repeaters may I put on an Ethernet? You cannot keep plugging more repeaters and add more cables to an Ethernet indiscriminately and expect it to work. With too large a networks, the protocol which keeps the number of collisions down (known as CSMA/CD) fails to do that. The protocol documents supply rules-of-thumb which, if followed, prevent this from occurring. If you break them, you may be risking large performance degradations. The latest version of the rules-of-thumb (which have been updated over time as new features like 10BASE-T have been added to the protocol) are in the IEEE 802.3 document describing 10BASE-T, specifically IEEE Std 802.ei-1990 in the section called "System Considerations for Multisegment 10 Mb/s Baseband Networks" (When 10BASE-F is released later, this section will be updated again). The rules refer to the piece of the LAN that is between repeaters as a segment and refer to 4 kinds: 10BASE5 (i.e. "classic" Ethernet) and 10BASE2 (i.e., ThinWire Ethernet) both classified as "Coax" segments and FOIRL (fiber inter-repeater links) and 10BASE-T, both classified as "Link" segments, and both of which have the property that you can attach things only to their ends. The basic repeater rule is that between any two stations on the LAN, there may be at most 4 repeaters and three coax segments. In addition, there are length restrictions on the segments which are designed to keep CSMA/CD working properly: 10BASE5 500 meters 10BASE2 185 meters FOIRL 500 meters (1000 meters in some cases) 10BASE-T 100 meters (or more) FOIRL links can be 1000 meters if you have at most 3 repeaters between stations instead of 4. 10BASE-T links can be longer if the cable will support it: CSMA/CD is not the limiting factor on 10BASE-T. For the purposes of this discussion, bridges, routers, and gateways are "stations" since the CSMA/CD protocol does not pass through them. Thus if you discover these rules prevent you from putting a repeater in the network where you need one, then you can put a bridge there instead, or perhaps split the LAN somewhere else using a bridge. 5. Should I use "manageable" hubs, concentrators, etc on my LAN? This is a controversial question also. Vendors have attempted to make hubs and concentrators that require little training & manpower to manage & troubleshoot, and they will attempt to convince you that they have succeeded. You pay a premium for "manageability". Those who remain skeptical wonder how much the management features are ever used: for example, management allows you to turn on & off ports from an operator's console; how often do you need to do such a thing? Also, some of the benefits attributed to management packages are simply due to good record keeping, something which the administrator must find the manpower to accomplish with a management package or without one (presumably with a simple dbms, which can often be tailored more to the administrators needs). 6. Which LAN technology should I use? Arcnet? FDDI? Token Ring? 10BASE-T? A controversial question. Some questions & answers from the 12/91 BIG-LAN Reader Survey: "When you install a LAN, which "Technology" (e.g. Ethernet, Token Ring) do you prefer?" 37 responders said Ethernet; 2 said "pick one and stick with it"; 1 said token ring. "If you have experience with two or more LAN technologies, which have you found works better?" Answers received: "Ethernet works best" 7 "Ethernet works better than Token Ring" 4 "Depends on application" 1 "Ethernet works better than ARCnet" 1 "Ethernet works better than Broadband" 1 "Ethernet best, Localtalk 2nd, ARCnet 3rd" 1 "Ethernet works better than PhoneNet" 1 "Token Ring works best" 1 7. What is the ideal cable to install in a new building? Distribution runs, i.e., phone closet to room: Best possible thing to do is to leave usable pathways for future expansion. Whatever you do, install at least 2 pair and probably 4 pair of data grade unshielded twisted pair. It will always have uses. Install something else too if you are tied to a particular vendor. Multimode fiber might become popular in the future but that is a gamble. Riser runs, i.e., phone closet to phone closet: it is imperative to leave usable pathways for future expansion. For Ethernet, ThinWire is a usable riser cable, multimode fiber is possible too. 8. What is the ideal cable to install between buildings on a campus? Trunks, i.e., cables into the building: pathways for future expansion very valuable. Multimode fiber is useful, run 24 fibers if you can. Use cable with some single mode too. Run several times what you need initially and leave a lot of the unused fiber unterminated for the time being. Cable pulling & termination are much more costly than the cable itself. 9. Whose routers are recommended? Question & answer from the 12/91 BIG-LAN Reader Survey: "Name some router vendors whose routers you have used and recommend:" Cisco got 30 mentions; Wellfleet 4; PCRoute 2; Proteon 2; Apple 1; DEC 1; Network Systems 1; Shiva 1; Vitalink 1; 3COM 1. 10. Whose bridges are recommended? Question & answer from the 12/91 BIG-LAN Reader Survey: "Name some bridge vendors whose routers you have used and recommend:" DEC got 6 mentions; Retix 5; BICC 3; Cabletron 3; 3COM 3; Cisco 2; PCBridge 2; Vitalink 2; ACC 1; Clearpoint 1; Datability 1; Develcon 1; Dowty Scanet 1; HP 1; IBM (Token Ring) 1; Network Application Technology 1; PCBRoute 1; Wellfleet 1. 11. Whose Ethernet equipment are recommended? Question & answer from the 12/91 BIG-LAN Reader Survey: "Name some Ethernet concentrator/transceiver/repeater vendors whose Ethernet equipment you have used and recommend:" Cabletron got 20 mentions; BICC 8; DEC 8; HP 4; Synoptics 4; David 3; Lantronix 3; Gandalf 2; Lannet 2; Pirelli Focom 2; Acton 2; Allied Telesys 1; AMP 1; Asante 1; Chipcom 1; Dowty Scanet 1; Dupont Electroptic 1; EAZY 1; Fibermux 1; Hirschmann 1; IMC Network Corporation 1; NetCor Transceivers 1; Sension 1; 3COM 1. 12. Whose Token Ring equipment are recommended? Query and answers from the 12/91 BIG-LAN Reader Survey: "Name some Token Ring equipment vendors whose Token Ring equipment you have used and recommend:" IBM was mentioned by 6 responders; FiberMux 1; Madge 1; Synoptics 1. 13. Whose FDDI equipment are recommended? Query and answers from the 12/91 BIG-LAN Reader Survey: "Name some FDDI equipment vendors whose FDDI equipment you have used and recommend:" Cisco was mentioned by 6 responders; DEC 2; Tymeplex 2; ALCATEL 2; AT&T 1; Synernetics 1; Tekelec 1. 14. What PC network software is recommended? Query and answers from the 12/91 BIG-LAN Reader Survey: "Name some PC network software vendors whose PC network software you have used or recommend:" Novell was mentioned by 19 responders; FTP Software 14; Sun 8; DEC 3; Apple 2; Farallon 2; InterCon 2; 3COM 2; Beame and Whiteside 1; Hummingbird Communications 1; IBM 1; Microsoft 1; NCSA 1; Neon Software 1; Network Application Technology 1; Sitka 1. 15. What protocols should run on a campus-wide LAN? Query and answers from the 12/91 BIG-LAN Reader Survey: "Name some protocols that you use to interconnect your campus that you would recommend:" TCP/IP was mentioned by 39 responders; Appletalk 9; DECNET 9; IPX 9; LAT 2; Coloured Book 2; G.703 2; ISO CONS 2; X.25/HDLC 1; XNS 1. 16. What software is recommended for managing a campus-wide LAN? Queries and answers from the 12/91 BIG-LAN Reader Survey: "Name some network management system that you use for the management of a campus LAN, that you recommend:" PSI SNMP was mentioned by 4 responders; Cabletron Remote LanView 2; Cisco NetCentral 2; Proteon Overview 2; SNMP 2; "A good drawing program" 1; DEC EMA 1; Map 1; NEMISYS from SEEL 1; SunNet Manager 1; TRW NMS 1. "Name other software that you use for the management of a campus LAN that you recommend:" FTP LanWatch was mentioned by 3 responders; EtherPeek 2; ping 2; AG Group Net Watchman for Appletalk 1; Apple Interpoll 1; Clarkson Packet Driver Utilities 1; DEC LAN Traffic Monitor 1; Domain Name System 1; inetrover 1; LAN Patrol 1; Neon Software Netminder Localtalk 1; Neon Software Netminder Ethernet 1; Network Application Technology EtherMeter 1; Shiva Net Manager 1; SNMP-Gawk (A SNMP-capable Gawk) 1; traceroute 1; Unix 1; Watchdog 1. 17. What terminal server is recommended? Query and answers from the 12/91 BIG-LAN Reader Survey: "Name vendors of terminal servers that you use and recommend:" Cisco was mentioned by 13 responders; DEC 5; Xyplex 4; Datability 2; Xylogics 2; 3COM 2; Emulex 1; Lantronix 1; Netcomm 1; Spider 1; TRW 1. 18. Whose troubleshooting equipment are recommended? Query and answers from the 12/91 BIG-LAN Reader Survey: "Name some vendors of network troubleshooting equipment that you use and would recommend:" Network General was mentioned by 8 responders; HP 4; Tektronix 4; Cabletron 3; Novell 3; Spider 3; AG Group 2; Wandel and Goltermann 2; FOTEC 1; Neon Software 1. 19. What security products should I buy? Query and answers from the 12/91 BIG-LAN Reader Survey: "Name some security products that you use to maintain security on your campus LAN that you recommend:" The answers reflected the lack of obvious products to choose from. Responses included "Athena Kerberos", "Encryption in Net3270", "Extended TACACS', "Host security", "Physical security", "Router access control lists", "SecurID", "Virus Scan", and "Windows Workstation". 20. Should the names of devices on my campus LAN have subdomains? Example of name without subdomain: bigvax.sequoia.edu; example with subdomain: bigvax.acs.sequoia.edu. It is possible to run networks of thousands of computers without the bother of subdomains, but they have some advantages. Queries and answers from the 12/91 BIG-LAN Reader Survey: "For Internet names of nodes on a campus network that supports TCP/IP, do you prefer the use of subdomains?" 27 responders said yes, 5 said no, 2 said it depends. "If you have worked on a campus that utilizes subdomains and one that does not, which does your experience tell you is the better way to administer names in a campus network?" 5 responders said the LAN with subdomains worked better; 2 said the LAN without subdomains worked better. One responder claimed that a good rule of thumb is that a LAN with more than 4000 stations works better with subdomains. 21. Should client stations use POP? Should they use just SMTP? Should I use some non-TCP/IP protocol for mail to/from client stations? Query and answers from the 12/91 BIG-LAN Reader Survey: "For client station's mail, which do you prefer: SMTP; TCP/IP-based client-server protocols (e.g. POP, POP2, etc); other LAN protocols?" 10 responders preferred TCP/IP-based client-server protocols (e.g. POP, IMAP, PCMAIL); 7 preferred SMTP; 4 said "use all three"; 3 preferred users signing onto a host system; 2 preferred other LAN protocols; 1 said "SMTP and TCP/IP-based client-server protocols"; 1 said "SMTP and X.400". 22. Should I enable SQE/heartbeat? This is a very brief discussion of SQE Test and CPT (both commonly referred to as "heartbeat") for IEEE 802.3 and Ethernet. For really gory details, see the appropriate documents, IEEE standard 802.3, ISO standard 8802-3, and the DIX Ethernet V2 Standard. (The first 2 references are, in theory, identical.) First, SQE Test (often misleadingly shortened to "SQE" by vendors) and CPT are not quite the same thing. CPT is a part of DIX Ethernet Version 2 and is simply a test of collision detection functionality in the MAU (that's the IEEE 802.3 name for a transceiver, Media Access Unit). It is ALWAYS present in Ethernet V2 MAUs and can't ever be disabled (without modifying the hardware). It is required for correct operation of ALL Ethernet V2 equipment. SQE Test, on the other hand, is part of the 802.3 specification and performs a number of MAU tests and "reports" to the controller if all is well. The "report" is in the form of a pulse nearly identical to the V2 CPT pulse, but with slightly differing timing specifications. It should be switchable, as 802.3 requires SQE Test for all terminal equipment, but prohibits it for repeaters. SQE Test and Heartbeat both appear as a signal in the collision lines from the MAU to the controller after every write. This is why MAUs with SQE Test enables and with displays show a collision every time they show a write. THIS IS NORMAL! Quick digression: What is a collision? Of course, we all know that a collision is when two controllers start to transmit at the same time (more of less) and that when this happens both will stop and wait for a random interval and then retransmit if carrier is not present. This function is critical to proper network operation. A MAU which can't detect a collision can mess up a network badly. This makes it critical to be able to quickly isolate "broken" MAUs. If you don't understand this, read any of the old papers on multiple access nets, especially the old Aloha Net. In practice, MAUs hardly ever fail. BUT IF ONE DOES, YOU MAY HAVE A BIG PROBLEM! While SQE Test indicates a bit more than heartbeat did and is slightly different in both timing and electrical characteristics, they are essentially the same from the perspective of most terminal equipment and you can replace an Ethernet V2 MAU with an 802.3 MAU with SQE Test enabled most of the time. (A notable exception is an Ethernet repeater which really requires an Ethernet V2 MAU. There may be others.) You can even replace an 802.3 MAU with an Ethernet V2 one most of the time. In fact, there are "fixes" for some Ethernet V2 MAUs to disable heartbeat and make them into something like an 802.3 MAU with SQE Test disabled. This also seems to work almost all the time. Anyone still with me? OK RULE FOR SQE Test. Always turn it on except for repeaters. There should be no exceptions to this rule, but there are. Some manufacturers can't seem to read standards (or just don't care). As a result there are some terminal devices that get upset when they see SQE Test. I have been told that this is true of the cisco AGS, but not the IGS. Not that there is any documentation on this. Several email exchanges with cisco folks have not clarified this. There is one BIG special case, the Ethernet fan-out box, most commonly a DEC DELNI. This box has only one MAU, so it repeats the CPT (it's a V2 device) that it sees from the MAU on the "master" port. If the master port is disabled, CPT is generated internally to keep things happy. But, what if you plug a repeater into a DELNI? You can disable CPT by using an 802.3 MAU with SQE Test disabled. or, if you don't use the master port, turn it on and plug an Ethernet loopback connector into the master port. In either case, CPT is disabled to ALL PORTS! No way around this. DELNIs produce other oddities. They shorten the total maximum length of the AUI cable used between the system and the MAU to 35 meters. (And don't forget to include the length of the cable between the interface and the connector on the rear of the cabinet.) This number is the sum of the cable from the host to the DELNI and from the DELNI to the MAU. Two 20 meter cables and you are over the limit! Because of these and other oddities, I try to avoid DELNIs. And I NEVER EVER plug a repeater of any type into one. Other companies make 802.3 equivalents to the DELNI on which SQE Test may be switched on each port. While this fixes one problem, the timing concerns of fan-out boxes remains. Buyer beware! Neither 802.3 nor Ethernet V2 standards cover fan-out boxes in any way, so there is no way to really claim that they meet standards (or don't). We've now covered the basics. So what happens when a MAU fails? In theory, every time it transmits a packet, an error is logged. This happens on some equipment. But most software I've dealt with simply ignores the error flag and does nothing. So SQE Test makes absolutely no difference to these systems. THIS IS BAD SOFTWARE DESIGN. Once in a while a MAU does fail. If it is on some device that does not log SQE Test failures or has a MAU with SQE Test turned off, you don't know what is happening. If you are on 10baseT, it can be isolated to a hub pretty quickly, but on coax you are reduced to segmenting the cable (physically disconnecting it) until you have isolated the problem. This is NOT fun and makes the network manager very unpopular since the network tends to be down for a LONG time. It took about 4 hours last time I had this problem and could have taken longer. What's a network manager supposed to do? Complain vigorously to vendors of equipment that don't adhere to the standard. Complain equally to vendors of software that doesn't bother to log the failures. SNMP is no good if the agents don't have any information to send out. End of Memo: BIG-LAN Frequently Asked Questions .