Busy BIND + 5.2.1 = UDP Packet Loss
From: Leo Bicknell (bicknell_at_ufp.org)
Date: 10/27/04
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Date: Wed, 27 Oct 2004 10:14:19 -0400 To: freebsd-hackers@freebsd.org
I recently upgraded a fairly busy nameserver to FreeBSD 5.2.1, and
I'm seeing packet loss from time to time on the box. I've done
some digging, and the box seems to be dropping UDP packets. Netstat
output:
udp:
177604011 datagrams received
0 with incomplete header
7 with bad data length field
2735233 with bad checksum
83753 with no checksum
205540 dropped due to no socket
1917 broadcast/multicast datagrams dropped due to no socket
10627437 dropped due to full socket buffers
0 not for hashed pcb
164033877 delivered
169793422 datagrams output
The "dropped due to full socket buffers" seems to be the issue. I
am also concerned by the number of packets with bad checksums, but
I have no previous data point.
I am seeing loss with DNS, but also with ping and given the few pauses
in my ssh sessions with TCP as well. I don't see anything remarkable
with the TCP or ICMP statistics. I don't think there's anything wrong
in MBUF land, statistics here for reference:
% netstat -m
mbuf usage:
GEN cache: 0/256 (in use/in pool)
CPU #0 cache: 335/672 (in use/in pool)
Total: 335/928 (in use/in pool)
Mbuf cache high watermark: 512
Maximum possible: 51200
Allocated mbuf types:
291 mbufs allocated to data
14 mbufs allocated to ancillary data
16 mbufs allocated to fragment reassembly queue headers
14 mbufs allocated to socket names and addresses
1% of mbuf map consumed
mbuf cluster usage:
GEN cache: 0/152 (in use/in pool)
CPU #0 cache: 289/400 (in use/in pool)
Total: 289/552 (in use/in pool)
Cluster cache high watermark: 128
Maximum possible: 25600
2% of cluster map consumed
1336 KBytes of wired memory reserved (49% in use)
0 requests for memory denied
0 requests for memory delayed
0 calls to protocol drain routines
The only other thing I found of interest was some interrupt drops:
% sysctl -a | grep drops
net.inet.ip.intr_queue_drops: 13981
So, given the traffic profile (nameserver, heavy UDP) and the info
here can someone help point me in the right direction? I'm not sure
where to go from here?
--
Leo Bicknell - bicknell@ufp.org - CCIE 3440
PGP keys at http://www.ufp.org/~bicknell/
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