babeld incorrectly handles retraction updates when no router-id precedes the update TLV

[fblaese]

We observed quite a lot of "Received prefix with no router id" + "Couldn't parse packet" log messages in a relatively large babel network lately. This only affects interfaces with bird neighbours.

After some debugging I was able to identify that this problem is caused by messages sent by bird containing Update TLVs with metric 65535 (retraction), but without a preceding router-id. This causes babeld to ignore this update at

babeld/message.c

Lines 721 to 724 in aa29624

	if(!have_router_id && message[2] != 0) {
	fprintf(stderr, "Received prefix with no router id.\n");
	goto fail;
	}

The babel-RFC doesn't seem to require Update TLVs to be preceeded by a router-id TLV, if the update is a retraction (metric == 0xffff).
It looks like babeld is handling this case correctly for wildcard retractions by excluding AE == 0 from this error check. This check probably also needs to exclude metric == 0xffff, but I haven't verified if that results in correct behavior.

[jech]

Hopefully fixed in d3734a1.