romkey@kaos.UUCP (John Romkey) (05/15/88)
Bill, I hate to do this, but I don't like proxy ARP at all. There are two reasons for why: First, there are too many network media that don't use ARP for my taste. ARPANET, X.25, ProNET-10. Maybe FDDI won't? I look at what you said about these media this way: you're going to have to support default gateways on them. You want the vendor to support it. The vendor's IP layer should probably be pretty media-independent, so if you've got default routers working in the software when you hook up a system to the ARPANET, you've basically got what you need for ethernet too. So it's not really an extra work to support it for networks other than the non-ARP media. Second, I had a really bad experience with an ethernet at MIT that had a proxy ARP router on it a few years ago. Dave Bridgham was setting up a second IP subnet on an ethernet at LCS. But a strange thing was happening - his packets were disappearing. The proxy ARP router was sending out ARP replies few milliseconds after the host Dave was trying to talk to and it ended up gobbling up all the packets. It took us a long time to track down the problem. I think there are situations where you might want to set up a second, test IP subnet or network on an network cable which already has a different IP subnet or network on it, and that proxy ARP routers which might believe they're doing exactly the right thing would make it impossible to do this. So proxy ARP is unacceptable to me. -- - john romkey UUCP: romkey@kaos.uucp ARPA: romkey@xx.lcs.mit.edu ...harvard!spdcc!kaos!romkey Telephone: (617) 776-3121
philipp@LARRY.MCRCIM.MCGILL.EDU (Philip A. Prindeville) (05/17/88)
I think there are situations where you might want to set up a second, test IP subnet or network on an network cable which already has a different IP subnet or network on it, and that proxy ARP routers which might believe they're doing exactly the right thing would make it impossible to do this. So proxy ARP is unacceptable to me. But you should be able to configure a router to not know about a network, and therefore not answer requests about it (to `unknow' the network, as it were). If you can't do this, it reflects a flaw in the implementation, not the protocol. -Philip
dab@ALLSPICE.LCS.MIT.EDU (05/17/88)
Actually, there was one other factor that caused proxy-ARP to lose in that case. This was the use of a default route in the other gateway. It didn't actually know a route to this test subnet I was setting up, it just thought it did (via its default route). So after proxy-ARPing the address I was trying to get to, it forwarded the packet off to the ARPA gateway (its default route), which forwarded the packet off to some random core gateway (its default route) which hopefully dropped it before it became an alligator in Dave Mill's swap. David Bridgham
romkey@kaos.UUCP (John Romkey) (05/19/88)
In article <8805170444.AA20271@Larry.McRCIM.McGill.EDU> philipp@LARRY.MCRCIM.MCGILL.EDU (Philip A. Prindeville) writes: >But you should be able to configure a router to not know about a >network, and therefore not answer requests about it (to `unknow' >the network, as it were). If you can't do this, it reflects a >flaw in the implementation, not the protocol. > >-Philip Suppose I don't own and run all the routers. Suppose the university or corporate telecommunications office does, or suppose BBN runs one of them, or the company down the street. I don't necessarily have control over all the computers on my network, and the level of effort needed to go through to get the necessary changes done to some of them for 15 minutes of testing may be prohibitive. -- - john romkey UUCP: romkey@kaos.uucp ARPA: romkey@xx.lcs.mit.edu ...harvard!spdcc!kaos!romkey Telephone: (617) 776-3121
ralphw@ius3.ius.cs.cmu.edu (Ralph Hyre) (05/20/88)
In article <882@kaos.UUCP> romkey@kaos.UUCP (John Romkey) writes: > >Bill, > >I hate to do this, but I don't like proxy ARP at all. ... >First, there are too many network media that don't use ARP for my >taste. ARPANET, X.25, ProNET-10. Maybe FDDI won't? I suppose I should give Phil Karn a chance to say this first, but AMPRnet (Amateur Packet Radio, network 44) generally won't - hidden terminal problems and unreliable broadcast performance make it impractical. Unfortunately, ARP has become too popular, so that people almost always think of trying to use it to help with routing. -- - Ralph W. Hyre, Jr. Internet: ralphw@ius2.cs.cmu.edu Phone:(412)268-{2847,3275} CMU-{BUGS,DARK} Amateur Packet Radio: N3FGW@W2XO, or c/o W3VC, CMU Radio Club, Pittsburgh, PA
karn@thumper.bellcore.com (Phil R. Karn) (05/21/88)
> I suppose I should give Phil Karn a chance to say this first, but > AMPRnet (Amateur Packet Radio, network 44) generally won't - hidden > terminal problems and unreliable broadcast performance make it impractical. My code, written specifically for AMPRNET, does use ARP. We even have our very own officially registered "hardware type" -- see the Assigned Numbers RFC. ARP on amateur packet radio works exactly like it does on Ethernet. Lost ARP requests aren't a problem, since there'll be a retransmission (from TCP or whatever) that simply gets turned into another ARP request. There being no formal broadcast address in the AX.25 link layer protocol, however, we had to define our own -- "QST". (You hams out there will understand the significance of these letters :-)). The only complication comes when "digipeaters" are used. These are simple store-and-forward repeaters that use a source routing feature in the link protocol. Broadcasting through digipeaters doesn't work, so you have to manually enter the proper source route and destination address into your ARP table. Phil
bdale@hpcsla.HP.COM (Bdale Garbee) (05/28/88)
/ srg@quick.COM (Spencer Garrett) / 2:15 am May 18, 1988 / >Why can't a host just ARP for any destination and expect the >appropriate gateway(s) to answer? If there were a hopcount >field in the ARP record, I think this would solve all the problems. We (N3CVL, K3MC, and myself) looked very hard about a year ago at doing something like this in the KA9Q Internet Package, to improve the situation on amateur packet radio, where almost noone can talk directly to anyone else, and so gateway/switch issues become very important. I eventually backed away from this idea when it became more clear to me that a distinction can and perhaps should be maintained between "routing" which is a logical operation, and "address resolution" which is (to me at least) a purely physical operation. However, my recent experience in designing and maintaining a sitewide LAN at work, including a bunch of discless clusters that for reasons of performance and cost will be subnetted by putting two ports on each discless server, have led me to be very interested in Proxy ARP, and other "ARP extensions". (If only HP would officially support Proxy ARP in HP-UX... sigh) My curiosity is up, therefore I also would be interested in comments on this subject. Bdale, N3EUA
rcb@cccvs1.ncsu.edu (Randy Buckland) (02/01/89)
Does anybody know where I can get a copy of proxy arp code for either an IBM PC/RT V2.2.1 or an Ultrix system V3.0? Randy Buckland rcb@ncsuvx.ncsu.edu
meggers@mothra.nts.uci.edu (Mark Eggers) (09/01/90)
Is there anywhere I can get proxy arp that will run on a Sun 4 ?? thanks - /mde/