Issues in Babel

[Ondrej Zajicek]

Hi Toke (and others)

I updated Babel to use microsecond timers [1] and during testing
i noticed several unrelated issues.


1) Hello expiration was not properly implemented, as i understand
RFC, it should reset the timer based on last packet hello interval
and time-out repeatedly until hello map is zero. Fixed in [2].


2) In some setups unicast seqno requests were sent repeatedly and seqno
was increased indefinitely due to last case in babel_handle_update(),
when the RFC specifies it should be done only if unfeasible route would
otherwise become best. Fixed in [3], by this condition handling all
unicast seqno requests:

  if (!feasible && (metric != BABEL_INFINITY) &&
      (!best || (r == best) || (metric < best->metric)))
    babel_unicast_seqno_request(e, s, nbr);

It also changes the behavior by sending seqno request when receiving
infeasible update if there is no previous route from that neighbor.


3) Seems like the fix of hello expiration caused that when neighbor
disappears, it is no longer removed timely and routes have to wait
for route timeout, which is about a minute for 4 s hello interval.

It seems that by RFC, we should recompute route metrics whanever rxcost
reported by IHU is changed, so IHU expiration should be enough to make
all related routes unreachable. Apparently, this is not done in BIRD.


4) Seems like we do not trigger updates when a route update with just
increased seqno due to forwarded unicast request is received. That also
slows convergence. IMHO we should do in babel_handle_update() something
like:

if (route_is_selected() && matching_entry_in_seqno_request_cache())
  babel_trigger_update()


Do you think that my interpretation of these issues and the fixes are correct?


[1] https://gitlab.labs.nic.cz/labs/bird/commit/8a76785a6fb23a64fcc93f998336794f605e2761
[2] https://gitlab.labs.nic.cz/labs/bird/commit/c7fa4efd701716a9c40620f2e3e8f0654b40b476
[3] https://gitlab.labs.nic.cz/labs/bird/commit/c54526afeb4187d55993c3ab777fcfe515837999

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."
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