I'm playing with a HP server that I'm trying to sell on ebay (HP ML350 dual-
CPU 128G of RAM) and decided to run some mail server benchmarks, running
Debian/Testing with Postfix delivering mail to a KVM VM on the same system.
Postfix isn't delivering mail as fast as it should and when I run dig on
addresses it's sending mail to I get errors like the following:
# strace -ff -s 2000 -o str dig -t mx a704.example.com
socket.c:1740: internal_send: 10.0.2.45#53: Invalid argument
socket.c:1740: internal_send: 10.0.2.45#53: Invalid argument
socket.c:1740: internal_send: 10.0.2.45#53: Invalid argument
; <<>> DiG 9.16.13-Debian <<>> -t mx a704.example.com
;; global options: +cmd
;; connection timed out; no servers could be reached
Presumably Postfix being unable to send mail is related to the same DNS issue.
bind(20, {sa_family=AF_INET, sin_port=htons(0),
sin_addr=inet_addr("0.0.0.0")}, 16) = 0
recvmsg(20, {msg_namelen=128}, 0) = -1 EAGAIN (Resource temporarily
unavailable)
write(4, "\24\0\0\0\375\377\377\377", 8) = 8
sendmsg(20, {msg_name={sa_family=AF_INET, sin_port=htons(53),
sin_addr=inet_addr("10.0.2.45")}, msg_
namelen=16, msg_iov=[{iov_base="86\1
\0\1\0\0\0\0\0\1\4a704\7example\3com\0\0\17\0\1\0\0)\20\0\0\0\0
\0\0\f\0\n\0\10's\367\265\16bx\354", iov_len=57}], msg_iovlen=1,
msg_controllen=0, msg_flags=0}, 0)
= -1 EINVAL (Invalid argument)
write(2, "socket.c:1740: ", 15) = 15
write(2, "internal_send: 10.0.2.45#53: Invalid argument", 45) = 45
write(2, "\n", 1) = 1
futex(0x7f5a80696084, FUTEX_WAIT_PRIVATE, 0, NULL) = 0
futex(0x7f5a80696010, FUTEX_WAKE_PRIVATE, 1) = 0
futex(0x7f5a8069809c, FUTEX_WAKE_PRIVATE, 1) = 1
futex(0x7f5a80698020, FUTEX_WAKE_PRIVATE, 1) = 1
sendmsg(20, {msg_name={sa_family=AF_INET, sin_port=htons(53),
sin_addr=inet_addr("10.0.2.45")}, msg_namelen=16, msg_iov=[{iov_base="86\1
\0\1\0\0\0\0\0\1\4a704\7example\3com\0\0\17\0\1\0\0)\20\0\0\0\0\0\0\f\0\n\0\10's\367\265\16bx\354",
iov_len=57}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = -1 EINVAL
(Invalid argument)
write(2, "socket.c:1740: ", 15) = 15
write(2, "internal_send: 10.0.2.45#53: Invalid argument", 45) = 45
write(2, "\n", 1)
Above is a sample of the strace output. If the argument is actually invalid
then that would be a dig bug. But the fact that it doesn't happen all the
time suggests that it's a race condition.
https://www.cyberciti.biz/faq/centos-redhat-debian-linux-neighbor-table-overflow/
As an aside talking to 2560 IPs on your LAN segment gives the kernel error
message "neighbour: arp_cache: neighbor table overflow", the above URL has the
solution.
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