Debug#

Check for duplicate packets#

If you have strange network behaviour it might be caused by duplicate packets.

In my case the most noticeable effect of duplicate packets is that interactive SSH sessions stutter: for example, when I keep the space button pressed, every now and then the terminal freezes for a moment.

You can check for duplicate packet with Wireshark using this filter

tcp.analysis.duplicate_ack or tcp.analysis.retransmission

If you get lots of duplicate packets try restarting all your network devices (router, switches, clients, etc…).

Rebooting, for the moment, seems the only viable fix.

See also

  • DuplicatePackets - Wireshark [1]

Drop AVM Fritzbox HomePlug packets#

If you run Wireshark in a network with certain AVM Fritzbox devices you will see lots of broadcast packets every seconds, such as this

15 1.780941119 AVMAudio_00:00:00 AtherosC_00:00:00 HomePlug AV 60 Qualcomm Atheros, OP_ATTR.REQ (Get Device Attributes Request)

GNU/Linux#

If you run this command on an interface you will see all the dropped packets

cat /sys/class/net/${interface}/statistics/rx_dropped

This is all unnecessary traffic which apparently you cannot disable from the router. What you can do is let the computers ignore all this traffic.

See also

  • firewall - How can I use iptables to drop packages for an invalid ether-type? - Server Fault [2]

  • Dropped HomePlug AV packets [3]

  1. install the netfilter package

    apt-get install nftables netfilter-persistent

  2. add this rule with a terminal or scripts

    nft table netdev filter '{ chain ingress { type filter hook ingress device eno1 priority 0; policy accept;  meta protocol {0x8912, 0x88e1} drop; }; }'

OpenWRT#

See also

  • OpenWRT/Lede AP: Drop FritzBox Homeplug Broadcasts · GitHub [4]

  1. install the ebtables package. Go to System -> Software

  2. click on Update lists...

  3. filter ebtables

  4. click on Install...

  5. go to Network -> Firewall -> Custom Rules

  6. append these commands

    ebtables -A FORWARD -p 88e1 -j DROP
ebtables -A FORWARD -p 8912 -j DROP

  7. go to System -> Reboot

  8. click on Perform reboot

Note

For some reason I can still see the packets when a computer is connected to an OpenWRT device using these rules which in turn is connected to the Fritzbox!

Footnotes