Re: dummynet & IP fragmentation bug

From: Alexander Motin (mav_at_alkar.net)
Date: 11/21/03

  • Next message: Clark Gaylord: "Re: Fail OVer routing" 
    To: freebsd-ipfw@freebsd.org, freebsd-net@freebsd.org
Date: Fri, 21 Nov 2003 12:52:50 +0200

    I successfully reproduced this on few different 4.8 routers.
    Does anybody knows what is this? How to fix or workaround this problem?

    Alexander Motin wrote:
    > 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
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