Re: [B.A.T.M.A.N.] [RFC PATCH] batman-adv: mitigate issue when empty vlan is received

On Sonntag, 6. Mai 2018 21:55:59 CEST Leonardo Mörlein wrote:

This patch is not a fix for the issue itself, but a fix for the other nodes, which are also influenced by the issue.

• Some (affected) nodes send TT announcements for an empty vlan (for now only seen with vlan_id = 0).
• This behaviour is a bug! Batman-adv nodes must not send TT announcements for empty vlans.
• The receiving batman-adv can not handle incoming TT announcements with empty vlans. (The crc check routine batadv_tt_global_check_crc() fails.)
• As the receiving node thinks, the crc is broken, it does a full table request then.
• The announcing node sends a TT full table to the receiving node then, which also contains the empty vlan, so *batadv_tt_global_check_crc()* fails again on the receiver side.
• This causes a lot of unneeded TT traffic. In Freifunk Hannover we decreased the amount of from ~20kpp/s to ~4kpp/s on our supernodes. We have ~800 nodes, which are connected via vpn to one of six supernodes. Those supernodes are connected with each other in a fully connected mesh.

Can you attach a (small) pcap of actual traffic which show a packet which triggers this behavior?

Thanks, Sven