Re: Mods to Steve Deering's "DF" scheme
mogul (Jeffrey Mogul) Thu, 08 March 1990 18:49 UTC
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From: mogul (Jeffrey Mogul)
Message-Id: <9003081849.AA11024@acetes.pa.dec.com>
Date: 8 Mar 1990 1049-PST (Thursday)
To: jmoy@proteon.com (John Moy)
Cc: mtudwg
Subject: Re: Mods to Steve Deering's "DF" scheme
In-Reply-To: jmoy@proteon.com (John Moy) / Tue, 6 Mar 90 15:37:10 EST.
<9003062037.AA00217@monk.proteon.com>
Go ahead and use the extra bit in the flags field. We're fixing this as I write (although you might want to check with the other vendors - my (old) IP specification still says that this bit MUST be 0), and by the time you guys start deploying MTU discovery people should have the updated Proteon software installed. Well, although the IP spec says "MUST be 0", it also says elsewhere that "an implementation ... must be liberal in its receiving behavior. ... [it] must accept any datagram that it can interpret (e.g., not object to technical errors where the meaning is still clear)." However, I think you're right that it would be a good idea to check to make sure that there aren't other routers which drop such packets. To that end, I did a little experiment: I changed the code in ip_output.c in my Ultrix kernel (but this should be applicable to anything even vaguely derived from 4.2BSD): *************** *** 79,80 struct mbuf *ip_insertoptions(); --- 79,84 ----- + #ifdef RFTEST + int rftest = 0; /* if set, then set the "RF bit" in originated p kts */ + #endif RFTEST + struct mbuf *ip_insertoptions(); *************** *** 108,109 ip->ip_off &= IP_DF; ip->ip_id = htons(ip_id++); --- 112,117 ----- ip->ip_off &= IP_DF; + #ifdef RFTEST + if (rftest) + ip->ip_off |= 0x8000; /* set the "RF bit" */ + #endif RFTEST ip->ip_id = htons(ip_id++); Your line numbers will vary, of course. Anyway, now I can control the "send RF" behavior by using adb (or an equivalent) to set/clear the "rftest" global flag. I find that one of the BARRNET routers fairly close to me drops these packets; I'm trying to find out what kind of router it is. Since I can't get very far with these packets, I encourage other people to put together a modified kernel and run a few traceroutes ... if we find non-Proteon routers that drop these packets, we should let people know ASAP. -Jeff
- Mods to Steve Deering's "DF" scheme Fred Bohle acc_gnsc
- Re: Mods to Steve Deering's "DF" scheme Jeffrey Mogul
- Mods to Steve Deering's "DF" scheme John Moy
- Re: Mods to Steve Deering's "DF" scheme Jeffrey Mogul