Re: ssh client_loop send disconnnect from Dom0 -> DomU (NetBSD 10.0_BETA/Xen)

[RVP <rvp%SDF.ORG@localhost>]

On Sat, 24 Jun 2023, Brian Buhrow wrote:

> In any case, The fact that you're getting regular delays on your pings suggests
> there is a delay between the time when the arp cache times out and when it gets refreshed.

This would be determined by `net.inet.arp.nd_delay' I think (on
-HEAD).

> As a consequence of that delay, if you have a high speed stream running when the cache times out,
> it's possible the send buffer of the sending process, i.e. sshd, is filling up before that
> cache gets refreshed and the packets can flow again.

In this case, the kernel would either block the sshd process or
return EAGAIN--which is handled. The kernel should only return a
EHOSTDOWN if `net.inet.arp.nd_bmaxtries' * `net.inet.arp.nd_retrans'
(ie. 3 * 1000ms) has passed without getting an ARP response. Even
on a LAN, this is pretty unlikely (even with that peculiarly short
30-second ARP-address cache timeout). Smells like a Xen+load+timing
issue (not hand-wavy at all there, RVP!). It would be interesting
to see the tcpdump capture from the DomU.

-RVP