Re: kern/57049: large TCP transfers NetBSD-Xen-Guest -> NetBSD-Xen-DOM0 abort with EHOSTDOWN

[Frank Kardel <kardel%netbsd.org@localhost>]

The following reply was made to PR kern/57049; it has been noted by GNATS.

From: Frank Kardel <kardel%netbsd.org@localhost>
To: gnats-bugs%netbsd.org@localhost, kern-bug-people%netbsd.org@localhost,
 gnats-admin%netbsd.org@localhost, netbsd-bugs%netbsd.org@localhost
Cc: 
Subject: Re: kern/57049: large TCP transfers NetBSD-Xen-Guest ->
 NetBSD-Xen-DOM0 abort with EHOSTDOWN
Date: Sat, 19 Nov 2022 18:12:36 +0100

 More data points:
 
 The arp state loops through following state sequence:
 
 host (ip-address) at MAC on xennet0 expired U
 host (ip-address) at MAC on xennet0 expired U
 host (ip-address) at MAC on xennet0 30s R
 host (ip-address) at MAC on xennet0 28s R
 host (ip-address) at MAC on xennet0 27s R
 host (ip-address) at MAC on xennet0 26s R
 host (ip-address) at MAC on xennet0 25s R
 host (ip-address) at MAC on xennet0 23s R
 host (ip-address) at MAC on xennet0 22s R
 host (ip-address) at MAC on xennet0 21s R
 host (ip-address) at MAC on xennet0 20s R
 host (ip-address) at MAC on xennet0 18s R
 host (ip-address) at MAC on xennet0 17s R
 host (ip-address) at MAC on xennet0 16s R
 host (ip-address) at MAC on xennet0 15s R
 host (ip-address) at MAC on xennet0 14s R
 host (ip-address) at MAC on xennet0 13s R
 host (ip-address) at MAC on xennet0 11s R
 host (ip-address) at MAC on xennet0 10s R
 host (ip-address) at MAC on xennet0 9s R
 host (ip-address) at MAC on xennet0 7s R
 host (ip-address) at MAC on xennet0 5s R
 host (ip-address) at MAC on xennet0 4s R
 host (ip-address) at MAC on xennet0 3s R
 host (ip-address) at MAC on xennet0 2s R
 host (ip-address) at MAC on xennet0 1s R
 host (ip-address) at MAC on xennet0 5s D
 host (ip-address) at MAC on xennet0 4s D
 host (ip-address) at MAC on xennet0 3s D
 host (ip-address) at MAC on xennet0 1s D
 host (ip-address) at MAC on xennet0 1s P
 host (ip-address) at MAC on xennet0 1s P
 host (ip-address) at MAC on xennet0 1s P
 host (ip-address) at MAC on xennet0 expired U
 host (ip-address) at MAC on xennet0 expired U
 host (ip-address) at MAC on xennet0 expired U
 host (ip-address) at MAC on xennet0 30s R
 host (ip-address) at MAC on xennet0 29s R
 host (ip-address) at MAC on xennet0 28s R
 host (ip-address) at MAC on xennet0 27s R
 
 tcpdump on xennet0:
 16:13:26.259366 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 
 host (MAC) tell guest-host, length 28
 16:13:27.259380 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 
 host (MAC) tell guest-host, length 28
 16:13:28.259414 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 
 host (MAC) tell guest-host, length 28
 16:13:29.259411 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 
 host (MAC) tell guest-host, length 28
 16:13:30.259434 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 
 host (MAC) tell guest-host, length 28
 16:13:31.259465 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 
 host (MAC) tell guest-host, length 28
 16:13:32.259516 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 
 host tell guest-host, length 28
 16:13:32.259606 ARP, Ethernet (len 6), IPv4 (len 4), Reply host is-at 
 MAC, length 28
 16:13:32.259608 ARP, Ethernet (len 6), IPv4 (len 4), Reply host is-at 
 MAC, length 28
 16:13:32.259609 ARP, Ethernet (len 6), IPv4 (len 4), Reply host is-at 
 MAC, length 28
 16:13:32.259609 ARP, Ethernet (len 6), IPv4 (len 4), Reply host is-at 
 MAC, length 28
 16:13:32.259610 ARP, Ethernet (len 6), IPv4 (len 4), Reply host is-at 
 MAC, length 28
 16:13:32.259610 ARP, Ethernet (len 6), IPv4 (len 4), Reply host is-at 
 MAC, length 28
 
 tcpdump on guest interfac in DOM0 connected to bridge0:
 16:26:03.745507 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 
 host (MAC) tell guest-host, length 28
 16:26:04.745537 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 
 host (MAC) tell guest-host, length 28
 16:26:05.745559 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 
 host (MAC) tell guest-host, length 28
 16:26:06.745599 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 
 host (MAC) tell guest-host, length 28
 16:26:07.745636 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 
 host (MAC) tell guest-host, length 28
 16:26:08.745725 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 
 host tell guest-host, length 28
 16:26:08.745793 ARP, Ethernet (len 6), IPv4 (len 4), Reply host is-at 
 MAC, length 28
 16:26:08.745797 ARP, Ethernet (len 6), IPv4 (len 4), Reply host is-at 
 MAC, length 28
 16:26:08.745800 ARP, Ethernet (len 6), IPv4 (len 4), Reply host is-at 
 MAC, length 28
 16:26:08.745803 ARP, Ethernet (len 6), IPv4 (len 4), Reply host is-at 
 MAC, length 28
 16:26:08.745812 ARP, Ethernet (len 6), IPv4 (len 4), Reply host is-at 
 MAC, length 28
 16:26:08.745815 ARP, Ethernet (len 6), IPv4 (len 4), Reply host is-at 
 MAC, length 28
 
 So we see that Replys are delayed (possibly queued) for 6 seconds. of 
 the 7 requests 6 are being replied to.
 Why do we see this delay/queueing on a busy bridge interface?
 arp.c has bridge conditional code.