tack ========= (this is a desktop machine with a simple IP configuration) Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 192.168.142.0 0.0.0.0 255.255.255.0 U 1 0 0 eth0 0.0.0.0 192.168.142.1 0.0.0.0 UG 0 0 0 eth0 olaf@tack:~$ /sbin/ifconfig eth0 Link encap:Ethernet HWaddr 00:22:15:fa:a1:8e inet addr:192.168.142.2 Bcast:192.168.142.255 Mask:255.255.255.0 inet6 addr: 2002:55b2:457a::2:2/128 Scope:Global inet6 addr: fe80::222:15ff:fefa:a18e/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:950450 errors:0 dropped:0 overruns:0 frame:0 TX packets:903163 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:662604312 (631.9 MiB) TX bytes:317938058 (303.2 MiB) Interrupt:17 As explained in readme.txt, the MTU of eth0 is modified to reproduce the problem. teck ========= (Ubuntu Laptop, connected via WLAN, again with a very simple config) (this is the machine that did NOT show the problem when it, rather than tick (see below), was the receiver of the UDP packets) olaf@teck:~$ route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 192.168.142.0 0.0.0.0 255.255.255.0 U 2 0 0 wlan0 169.254.0.0 0.0.0.0 255.255.0.0 U 1000 0 0 wlan0 0.0.0.0 192.168.142.1 0.0.0.0 UG 0 0 0 wlan0 olaf@teck:~$ ifconfig wlan0 Link encap:Ethernet HWaddr 4c:ed:de:0c:0c:c6 inet addr:192.168.142.130 Bcast:192.168.142.255 Mask:255.255.255.0 inet6 addr: fe80::4eed:deff:fe0c:cc6/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:503894 errors:0 dropped:0 overruns:0 frame:0 TX packets:328534 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:685286068 (685.2 MB) TX bytes:33875055 (33.8 MB) tick ========= Router machine. Basically has two local interfaces -- one wired (eth0) and one wireless (ath0) that are bridged in the linux kernel to create a bridge device (lanif) which all the IP communication targeted at the LAN (192.168.142.0/24) are routed over. There are some ppp interfaces for the internet connectivity and some VPNs, but those shouldn't be part of the problem here (they're still listed below for reference). The bridge device is set up like this: ifconfig eth0 0.0.0.0 ifconfig ath0 0.0.0.0 brctl addbr lanif brctl addif lanif eth0 brctl addif lanif ath0 ifconfig lanif up 192.168.142.1 netmask 255.255.255.0 detailed configuration: olaf@tick:~$ /sbin/route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 213.191.89.2 0.0.0.0 255.255.255.255 UH 0 0 0 ppp0 192.168.17.2 0.0.0.0 255.255.255.255 UH 0 0 0 ppp1 192.168.0.0 0.0.0.0 255.255.255.0 U 0 0 0 ppp1 192.168.142.0 0.0.0.0 255.255.255.0 U 0 0 0 lanif 0.0.0.0 0.0.0.0 0.0.0.0 U 0 0 0 ppp0 olaf@tick:~$ /sbin/ifconfig ath0 Link encap:Ethernet HWaddr 00:1B:2F:2B:C7:A2 inet6 addr: fe80::21b:2fff:fe2b:c7a2/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:2290 Metric:1 RX packets:2778378 errors:0 dropped:0 overruns:0 frame:0 TX packets:1971861 errors:0 dropped:94 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:702098634 (669.5 MiB) TX bytes:2531315932 (2.3 GiB) eth0 Link encap:Ethernet HWaddr 00:00:24:CC:CB:B8 inet6 addr: fe80::200:24ff:fecc:cbb8/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:5168016 errors:0 dropped:0 overruns:0 frame:0 TX packets:6224349 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:1203738487 (1.1 GiB) TX bytes:1754442486 (1.6 GiB) Interrupt:11 Base address:0x2000 eth1 Link encap:Ethernet HWaddr 00:00:24:CC:CB:B9 inet6 addr: fe80::200:24ff:fecc:cbb9/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:17169052 errors:0 dropped:0 overruns:0 frame:0 TX packets:16617843 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:2105326414 (1.9 GiB) TX bytes:456442081 (435.2 MiB) Interrupt:5 Base address:0x4100 lanif Link encap:Ethernet HWaddr 00:00:24:CC:CB:B8 inet addr:192.168.142.1 Bcast:192.168.142.255 Mask:255.255.255.0 inet6 addr: fe80::200:24ff:fecc:cbb8/64 Scope:Link inet6 addr: 2002:55b2:457a::2:1/128 Scope:Global UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:6278577 errors:0 dropped:0 overruns:0 frame:0 TX packets:7913895 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:1209097703 (1.1 GiB) TX bytes:4028697061 (3.7 GiB) lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:42255 errors:0 dropped:0 overruns:0 frame:0 TX packets:42255 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:8020490 (7.6 MiB) TX bytes:8020490 (7.6 MiB) ppp0 Link encap:Point-to-Point Protocol inet addr:85.178.69.122 P-t-P:213.191.89.2 Mask:255.255.255.255 UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1492 Metric:1 RX packets:447684 errors:0 dropped:0 overruns:0 frame:0 TX packets:293100 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:3 RX bytes:572338765 (545.8 MiB) TX bytes:19634404 (18.7 MiB) ppp1 Link encap:Point-to-Point Protocol inet addr:192.168.17.1 P-t-P:192.168.17.2 Mask:255.255.255.255 UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1500 Metric:1 RX packets:1342 errors:0 dropped:0 overruns:0 frame:0 TX packets:1357 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:3 RX bytes:599773 (585.7 KiB) TX bytes:90863 (88.7 KiB) tun6to4 Link encap:IPv6-in-IPv4 inet6 addr: 2002:55b2:457a::1:2/128 Scope:Global inet6 addr: ::85.178.69.122/128 Scope:Compat UP RUNNING NOARP MTU:1480 Metric:1 RX packets:1567 errors:0 dropped:0 overruns:0 frame:0 TX packets:1760 errors:9 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:1066556 (1.0 MiB) TX bytes:692190 (675.9 KiB) wifi0 Link encap:UNSPEC HWaddr 00-1B-2F-2B-C7-A2-00-00-00-00-00-00-00-00-00-00 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:1468032 errors:0 dropped:0 overruns:0 frame:41673 TX packets:2000809 errors:15207 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:280 RX bytes:421407449 (401.8 MiB) TX bytes:2622521267 (2.4 GiB) Interrupt:10