Open-Mesh » batman-adv

While the overall ARP overhead is greatly reduced, we generally still have many ARP Requests from gateway nodes / routers. In a 1000 node setup this is about 30kbit/s.

In a minimal setup with just two hosts (Linux 4.6-rc6, no batman-adv involved), one being a DHCP server, the other one a DHCP client, as well as one persistent TCP connection between them, I noticed that ARP packets are sent rarely. This seems to break the initial assumption, that at least one ARP exchange would take place during the 5min. DAT cache timeout.

In the test setup, during a ~37000 seconds (10h) interval, these were the only ARP packets showing up:

  5 106.241867 02:04:64:a4:39:d3 -> ff:ff:ff:ff:ff:ff ARP 60 Who has 192.168.123.1? Tell 192.168.123.50
  6 106.241958 02:04:64:a4:39:f2 -> 02:04:64:a4:39:d3 ARP 42 192.168.123.1 is at 02:04:64:a4:39:f2
 14 111.246595 02:04:64:a4:39:f2 -> 02:04:64:a4:39:d3 ARP 42 Who has 192.168.123.50? Tell 192.168.123.1
 15 111.247439 02:04:64:a4:39:d3 -> 02:04:64:a4:39:f2 ARP 60 192.168.123.50 is at 02:04:64:a4:39:d3
2092 5217.550877 02:04:64:a4:39:d3 -> 02:04:64:a4:39:f2 ARP 60 Who has 192.168.123.1? Tell 192.168.123.50
2093 5217.550911 02:04:64:a4:39:f2 -> 02:04:64:a4:39:d3 ARP 42 192.168.123.1 is at 02:04:64:a4:39:f2

Which would of course be insufficient to keep the DAT Cache fully up to date during the time a client is connected.