dummynet & IP fragmentation bug

[Alexander Motin]

Hello.

I have one strange problem with dummynet & IP fragmentation.

I have FreeBSD 4.8-RELEASE router with few interfaces:
em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
         options=3<rxcsum,txcsum>
         inet 195.248.191.172 netmask 0xffffffc0 broadcast 195.248.191.191
         ether 00:30:48:20:8e:7e
         media: Ethernet autoselect (1000baseTX <full-duplex>)
         status: active
ng4: flags=88d1<UP,POINTOPOINT,RUNNING,NOARP,SIMPLEX,MULTICAST> mtu 1492
         inet 195.248.191.172 --> 212.86.231.58 netmask 0xffffffff

Interface ng4 have MTU 1492 because it is PPPoE link.
When I do not use dummynet on router and somebody send a big 
(>1492bytes) packet to 212.86.231.58 with DontFragment flag set router 
generates ICMP reply message (Fragmentation Needed). This is correct.

But when I use dummynet on that interface:
10170 pipe 10009 ip from any to any out xmit ng4
10175 allow ip from any to any via ng4

10009: 128.000 Kbit/s    0 ms   50 sl. 1 queues (1 buckets) droptail
     mask: 0x00 0x00000000/0x0000 -> 0x00000000/0x0000
BKT Prot ___Source IP/port____ ____Dest. IP/port____ Tot_pkt/bytes 
Pkt/Byte Drp
   0 udp   195.248.191.65/53      212.86.231.58/1118  50965 28380582  0 
    0 143

router stops sending that ICMP messages. Pipe is not overflowed at that 
tme, it is empty.

-- 
Alexander Motin