From owner-freebsd-net Thu Oct 18 16:49: 5 2001 Delivered-To: freebsd-net@freebsd.org Received: from boreas.isi.edu (boreas.isi.edu [128.9.160.161]) by hub.freebsd.org (Postfix) with ESMTP id 262F737B407 for ; Thu, 18 Oct 2001 16:49:03 -0700 (PDT) Received: from isi.edu (hbo.isi.edu [128.9.160.75]) by boreas.isi.edu (8.11.6/8.11.2) with ESMTP id f9INn2O15585; Thu, 18 Oct 2001 16:49:02 -0700 (PDT) Message-ID: <3BCF6A6E.5000302@isi.edu> Date: Thu, 18 Oct 2001 16:49:02 -0700 From: Lars Eggert User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:0.9.4) Gecko/20010924 X-Accept-Language: en, de MIME-Version: 1.0 To: net@freebsd.org, Yu-Shun Wang Subject: ARP & IP fragments Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-freebsd-net@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.org Hi, we're seeing a strange thing happening, related to ARP and IP fragments. In the tcpdump below, ifc is trying to send a large UDP message (~3x MTU) to dee. It does not have dee's MAC address in its ARP cache (happens both after an ARP timeout or an explicit ARP cache flush.) The ARP request/reply succeed, but then only the third IP fragment makes it out onto the wire: 16:36:27.550259 arp who-has dee.isi.edu tell ifc.isi.edu 16:36:27.550519 arp reply dee.isi.edu is-at 0:2:b3:2c:3:d9 16:36:27.550538 ifc.isi.edu > dee.isi.edu: (frag 11094:102@2960) (ttl 64, len 122) The IP protocol stats (netstat -s -p ip) go up correctly on ifc, "output datagrams fragmented" by 1 and "fragments created" by 3. The fragments never seem to make it into bpf or out on the wire though, and I see no other stats change or errors appear. This is with 4.4-RELEASE, but has happened (at least) since 4.2-RELEASE. Repeating this when an ARP entry for dee is present results in all three fragments to be sent: 16:36:54.255363 ifc.isi.edu.1309 > dee.isi.edu.1323: udp 3054 (frag 53580:1480@0+) (ttl 64, len 1500) 16:36:54.255369 ifc.isi.edu > dee.isi.edu: (frag 53580:1480@1480+) (ttl 64, len 1500) 16:36:54.255376 ifc.isi.edu > dee.isi.edu: (frag 53580:102@2960) (ttl 64, len 122) Any clues? Thanks, Lars -- Lars Eggert Information Sciences Institute http://www.isi.edu/larse/ University of Southern California To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message