Date: Wed, 10 Aug 2005 16:19:16 +0200 From: Claudio Jeker <cjeker@diehard.n-r-g.com> To: freebsd-net@freebsd.org Subject: Re: Stranges with ARP Message-ID: <20050810141938.GF31018@diehard.n-r-g.com> In-Reply-To: <E1E2qIp-000NEB-00.steve-langdon-mail-ru@f24.mail.ru> References: <E1E2qIp-000NEB-00.steve-langdon-mail-ru@f24.mail.ru>
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On Wed, Aug 10, 2005 at 05:07:27PM +0400, Steve Langdon wrote: > Hello all. > > Help me to solve a strange conduct. > I want to have permanent bundle with IP->MAC for users in our network to > have some security. So, once my user's MAC doesn't appear in my ARP > table, I have to block by ``arp -S ..' his IP with MAC generated by my > script with prefix d1:fa:28. > > One day I have a phone talk with my user, he make complaints against slow speed in Internet. When I have checked his IP I feel a terrible :) > > tcpdump: listening on rl0 > 18:48:11.339543 213.238.62.65.80 > 192.168.57.90.1072: . 2091947455:2091948915(1460) ack 140637902 win 7441 (DF) [tos 0x60] > ^C > 561 packets received by filter > 0 packets dropped by kernel > > Traffic comes to that user! > > root@router:~ % arp -a | grep -w 192.168.57.90 > ? (192.168.57.90) at d1:fa:28:ec:87:98 on rl0 permanent [ethernet] > root@router:~ % > > While user is blocked by _our_ generated MAC! Btw, could anyone advice > me how to block user IP block without touching ipfw (I think to use > route + ``-blackhole' to that user that have no his MAC in my ARP > table), any ideas? > > > root@router:~ % arping 192.168.57.90 > ARPING 192.168.57.90 > 60 bytes from 00:00:f0:87:4b:ca (192.168.57.90): index=0 time=2.724 msec > 60 bytes from 00:00:f0:87:4b:ca (192.168.57.90): index=1 time=9.966 msec > ^C > --- 192.168.57.90 statistics --- > 2 packets transmitted, 2 packets received, 0% unanswered > root@router:~ % > > His real MAC is 00:00:f0:87:4b:ca. I can't belave this could be. Whats > wrong? > As I think all traffic must transmit to d1:fa:28:ec:87:98, NOT to > 00:00:f0:87:4b:ca and user's NIC must ignore that packet unless his > interface in PROMISC mode. Or I'm wrong? Come on have a look at the MAC address. d1:fa:28:ec:87:98. Ja ja ja d1. Remember the multicast bit of 802.11? No, its the LSB of the first octet. So your outgoing pings are actually multicasts. -- :wq Claudio
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