MPD 5.7 / fragmentation / packet loss?

[Frank Graf]

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

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