BIND and UDP tuning

Alex mysqlstudent at
Fri Sep 28 13:26:03 UTC 2018


On Fri, Sep 28, 2018 at 12:18 AM Lee <ler762 at> wrote:
> On 9/27/18, Alex <mysqlstudent at> wrote:
> > Hi,
> >
> >> Just a wild thought:
> >> It works with a lower speed line (at least I read it that way) but has
> >> problems with higher speeds.
> >> Could it be that the line is so fast that it "overtakes" the host in
> >> question?
> >>
> >> A faster incoming line will give less time between the packets for
> >> processing.
> >
> > No, I actually upgraded from a 65/20mbit to a 165/35mbit recently,
> > thinking it was too slow because it was happening at the slower speeds
> > as well. I've also implemented some basic QoS to throttle outgoing
> > smtp and prioritize DNS but it made no difference.
> Has your provider enabled qos?  I'd bet their dropping packets that
> exceed qos rate limits would be considered "working as expected".

I asked and they had no idea what that even meant. The technician that
was here replacing the modem also had no idea outside of what the
hardware does.

I've also asked on dslreports about this, and no one answered.

It certainly seems to be more pronounced now than it ever was in the
past. Sometimes so many queries are failing that it's impossible to
use the network.

> Which brings up the question of exactly what does SERVFAIL mean?  Can
> no response to a query result in SERVFAIL?  Is there a way to tell the
> difference between no response & getting a response indicating a
> failure?

Early in this thread or another, I provided a packet trace that showed
what appears to me to never have received the replies - it just times
out. Also, the "Server Failure" messages are always on the loopback
interface. I'd be happy to provide another trace if someone knows how
to properly read it. I really have no idea what's causing the problem.

Also, I recently raised the trace level to 99, but I don't see
anything in the logs beyond level 4. Where do I find what the
different trace levels are supposed to report?

27-Sep-2018 16:57:29.688 query-errors: info: client @0x7fc7b0169ac0 (
query failed (SERVFAIL) for at
26-Sep-2018 15:16:32.507 query-errors: debug 2: fetch completed at
../../../lib/dns/resolver.c:3927 for in 30.000092:
timed out/success

There are also tons of messages involving disabling EDNS:
27-Sep-2018 16:57:29.549 edns-disabled: debug 1: success resolving
'' (in
''?) after disabling EDNS

I've also just installed 'netdata', which is an app that reports on
system parameters, and find it frequently reporting messages like:
ipv4 tcp listen overflows = 4 overflows
inbound packets dropped = 22 packets
ipv4 udp receive buffer errors = 184 errors

I've also now made the following buffer adjustments based on this and
other perf tuning docs:
net.core.rmem_default = 8388608
net.core.rmem_max = 33554432
net.core.wmem_default = 52428800
net.core.wmem_max = 134217728
net.ipv4.udp_early_demux = 0
net.ipv4.udp_mem=764304 1019072 1528608
net.ipv4.tcp_rmem=16384 349520 16777216
net.ipv4.udp_rmem_min = 18192
net.ipv4.udp_wmem_min = 8192
net.core.netdev_budget = 10000
net.core.netdev_max_backlog = 2000


More information about the bind-users mailing list