Date: Sat, 3 Mar 2001 17:03:02 -0800 From: "Crist J. Clark" <cjclark@reflexnet.net> To: Larry Berland <stuyman@confusion.net> Cc: Ted Mittelstaedt <tedm@toybox.placo.com>, John Baldwin <jhb@FreeBSD.ORG>, Doug Young <dougy@gargoyle.apana.org.au>, freebsd-questions@FreeBSD.ORG Subject: Re: Promiscuous Mode ?? Message-ID: <20010303170302.P89396@rfx-216-196-73-168.users.reflex> In-Reply-To: <Pine.NEB.3.96.1010303105937.29820B-100000@euphoria.confusion.net>; from stuyman@confusion.net on Sat, Mar 03, 2001 at 11:15:45AM -0800 References: <002901c0a2f1$cdb23440$1401a8c0@tedm.placo.com> <Pine.NEB.3.96.1010303105937.29820B-100000@euphoria.confusion.net>
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On Sat, Mar 03, 2001 at 11:15:45AM -0800, Larry Berland wrote: > > > On Fri, 2 Mar 2001, Ted Mittelstaedt wrote: > > > >[mailto:owner-freebsd-questions@FreeBSD.ORG]On Behalf Of John Baldwin > > >On 01-Mar-01 Doug Young wrote: > > >> Would someone please comment on the following. The machine is > > >> running fine so I don't believe its anything particularly bad, but I > > >> don't recall seeing that particular message previously. > > > > > >Do you use DHCP? Every time you get or renew a lease dhclient puts the > > >interface in promiscuous mode. > > > > No, it doesen't - DHCP is just another service, it requests via broadcast > > packets and listens for a unicast packet response on a specified port. > > > > Correct me if I'm wrong, but when you request a lease after you've first > come up (aka no IP) you put out in broadcast, and then the dhcp server > will reply to you via broadcast as well. However, since the client > doesn't necessarily know the broadcast (as they don't know their address > or the network address) they'd be using 255.255.255.255 or 0.0.0.0 until > they did, which would mean the dhcp server is binding to those addresses, > instead of just its normal IP and the broadcast IP for the network. Or > maybe i'm just insane. Basically, the point of this insane rant (I've > been awake far too long) is that the dhcp reply initially must be > broadcast, since the client has no clue what to listen to otherwise. But > since the client doesn't even know the broadcast address, does that mean > it gets its reply on 0.0.0.0 or 255.255.255.255, or does it just go > promisc to get the reply on the normal broadcast address? Looks like people are confusing IP broadcasts versus data layer broadcasts and some other stuff. But most of this is moot. Unless your provider's DHCP is broken, you only need to go into promiscuous mode that first time you get an address. Once you are up and running, your machine has a valid IP and it knows the IP of its DHCP server. Lease renewals should take place in unicast. For example, I just caught mine, # tcpdump -nevv 'port 68 && host myhost' tcpdump: listening on fxp0 16:46:45.991117 0:90:27:13:25:40 0:2:7e:e8:ac:0 0800 342: aaa.bbb.ccc.ddd.68 > eee.fff.ggg.hhh.67: xid:0x3691cf50 C:aaa.bbb.ccc.ddd vend-rfc1048 DHCP:REQUEST PR:SM+BR+TZ+DG+DN+NS+HN (ttl 64, id 21331) 16:46:46.096938 0:2:7e:e8:ac:0 0:90:27:13:25:40 0800 342: eee.fff.ggg.hhh.67 > aaa.bbb.ccc.ddd.68: xid:0x3691cf50 C:aaa.bbb.ccc.ddd Y:aaa.bbb.ccc.ddd S:eee.fff.ggg.hhh vend-rfc1048 DHCP:ACK SID:eee.fff.ggg.hhh LT:134676480 SM:255.255.255.0 DG:aaa.bbb.ccc.ddd.1 DN:"reflexnet.net" NS:64.6.204.18,64.6.192.66 (DF) (ttl 252, id 14961) Note that there was no broadcasting going on. However, if something is messed up on your network, specifically, if your machine cannot find its server, it can fall back to trying broadcasting again. -- Crist J. Clark cjclark@alum.mit.edu To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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