Date: Sat, 16 May 2015 10:10:19 +0200 From: Frank Graf <f.graf@firemail.de> To: freebsd-net@freebsd.org Subject: MPD 5.7 / fragmentation / packet loss? Message-ID: <5556FB6B.2030607@firemail.de>
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Hello, I'm using FreeBSD 10.0 with MPD Ver. 5.7 as a router to connect to my ISP with PPPoE. With one host on my network I've problems to connect through the FreeBSD router to the internet. With tcpdump I see the following ICMP messages from this host: "ICMP ip reassembly time exceeded" After some investigation I know that the Problem occurs on every host with a MTU of 1500 (MTU > 1492). Unfortunately I cannot decrease the MTU to 1492 (due to PPPoE) on this one host. For test purposes I have done some test with ping and a payload of 1500 from the FreeBSD router. This is a tcpdump trace from the MPD interface (ng0): fbsd-ip is the IP address of the FreeBSD router srv-ip is the IP address from a host connected to the internet Usually I get no successfull reply to the echo requests: No. Source Destination Protocol Length Info 133 fbsd-ip srv-ip IPv4 1496 Fragmented IP protocol (proto=ICMP 1, off=0, ID=ca88) [Reassembled in #134] 134 fbsd-ip srv-ip ICMP 60 Echo (ping) request id=0xb95e, seq=33/8448, ttl=64 (no response found!) 135 srv-ip fbsd-ip IPv4 1496 Fragmented IP protocol (proto=ICMP 1, off=0, ID=4c1b) 136 srv-ip fbsd-ip IPv4 32 Fragmented IP protocol (proto=ICMP 1, off=1472, ID=4c1b) Only once I got a succsessfull reply in seq. nr. 34: 137 fbsd-ip srv-ip IPv4 1496 Fragmented IP protocol (proto=ICMP 1, off=0, ID=ca89) [Reassembled in #138] 138 fbsd-ip srv-ip ICMP 60 Echo (ping) request id=0xb95e, seq=34/8704, ttl=64 (reply in 141) 139 srv-ip fbsd-ip IPv4 1496 Fragmented IP protocol (proto=ICMP 1, off=0, ID=4c77) [Reassembled in #141] 140 srv-ip fbsd-ip IPv4 32 Fragmented IP protocol (proto=ICMP 1, off=1472, ID=4c77) [Reassembled in #141] 141 srv-ip fbsd-ip ICMP 52 Echo (ping) reply id=0xb95e, seq=34/8704, ttl=58 (request in 138) The echo reply consists of 3 packets, but only 2 are usually received at the MPD interface ng0. On the physical WAN interface on the router always all (PPPoE) packets are received, I've checked this with tcpdump. It seems that one packet/fragment is dropped between the physical interface and the MPD (ng0) interface. The host 'srv-ip' is connected with ethernet and a MTU of 1500 to the internet, the echo reply consists of 2 packets. One of the packet is fragmented from the ISP router due to PPP encapsulation. Therefore the echo reply consists of 3 packets on the FreeBSD WAN interface. If I connect to the internet through the user PPP implementation of FreeBSD, the ping with a payload of 1500 is successfull. I've a 100 Mbit down / 40 Mbit up internet connection, the performance is poor (18 Mbit) with user PPP, therefore I'm using MPD. Is this a bug in MPD or configuration error? Is it possible to reach 100 Mbit throughput with user PPP? (CPU is at about 80% idle during a download) Are there any other PPP(oE) implementations for FreeBSD I can use? Thanks in advance. Frank _________________________________________________________________ Firemail.de Freemail - 10 GB für Mails und Daten POP3 und IMAP kostenfrei http://www.firemail.de/
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