Hi,
Ulf Samuelsson wrote:
> The desired functionality is that if communication stops,
> you want to send out ARP probes, before the entry is deleted.
>
> The current (pseudo) code of the neigh timer is:
>
> if (state & NUD_REACHABLE) {
> if (now <= "confirmed + "reachable_time")) {
> ... /* We are OK */
> } else if (now < "used" + DELAY_PROBE_TIME) { /* Never happens */
> state = NUD_DELAY;
> } else {
> state = NUD_STALE;
> notify = 1;
> }
>
> We never see the state beeing changed from REACHABLE to DELAY,
> so the probes are not beeing sent out, instead you always go
> from REACHABLE to STALE.
That's right.
> DELAY_PROBE_TIME is set to (5 x HZ) and "used"
> seems to be only set by the periodic_work routine
> when the neigh entry is in STALE state, and then it is too late.
> It is also set by "arp_find" which is used by "broken" devices.
>
In STALE state, neigh->used is set by neigh_event_send(), called
by neigh_resolve_output() via neigh->output().
> In practice, the second condition: "(now < "used" + DELAY_PROBE_TIME)" is
> never used.
> What is the intention of this test?
That's right. It is NOT used in normal condition unless
reachable time is too short.
>
> By adding a new test + parameter, we would get the desired functionality,
> and no need to listen for notifications or doing ARP state updates from
> applications.
>
> if (now <= "confirmed + "reachable_time")) {
> ... /* We are OK */
> + else if (now <= "confirmed + "reprobe_time")) {
> + state <= NUD_DELAY;
> } else if (now < "used" + DELAY_PROBE_TIME))) { /* Never happens */
> state <= NUD_DELAY;
> } else {
> state = NUD_STALE;
> notify = 1;
> }
>
> This way the entry would remain in REACHABLE while normal communication
> occurs,
> then it would enter DELAY state to probe, and if that fails, it goes to STALE
> state.
No, it is not what REACHABLE and DELAY mean.
>From RFC2461:
| REACHABLE Roughly speaking, the neighbor is known to have been
| reachable recently (within tens of seconds ago).
:
| STALE The neighbor is no longer known to be reachable but
| until traffic is sent to the neighbor, no attempt
| should be made to verify its reachability.
| DELAY The neighbor is no longer known to be reachable, and
| traffic has recently been sent to the neighbor.
| Rather than probe the neighbor immediately, however,
| delay sending probes for a short while in order to
| give upper layer protocols a chance to provide
| reachability confirmation.
--
Hideaki Yoshifuji <hideaki.yoshif...@miraclelinux.com>
Technical Division, MIRACLE LINUX CORPORATION
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