Good day bind experts -
Please can anyone advise the best way to optimize named's
UDP timeout settings for caching-only local resolver usage
over a slow network link - I can't seem to find any in the
Bv9ARM document specifically describing how named
implements UDP re-transmits - please could someone
point me at the right pages or place to look, besides
the source code, which I am reading now, if there are any ?
My problem is that at home my whole internet goes through
one 100M CAT-6 ethernet cable to a GSM 3G/4G modem (90% 3G WCDMA) ,
it seems no more than about 128 kilobyte/sec download & less upload
bandwidth is available, whenever my browser decides to download
something large (like a JavaScript blob) , then DNS requests
start timing out, the browser keeps re-issuing its requests,
and similar nasty feedback situations occur when the GSM
modem's DHCP lease expires and it has to re-setup its NAT for
the ethernet link, so all UDP requests time out for about
10 seconds, building up quite a backlog.
I have tried playing around with named.conf settings:
resolver-retry-interval 8;
resolver-retry-time 32;
max-retry-time 32;
but they don't seem to help - I still get a 'DNS freeze'
situation for about 10-30 seconds when the GSM modem
renegotiates its DHCP lease, during a yum / dnf 'update',
during large browser downloads or stream playing ...
My Linux v5.12.17 (Fedora-34) x86_64 box runs named 9.6.18
from the Fedora RPM, and hosts a Windows 10 VM, which is quite a
chatty DNS user, and runs a hostapd instance through which traffic from a
local network of 3 Android mobile phones use as their default
data connection, which also use the laptop's DNS server,
and send SIP voice traffic through my company's SIP server which I
maintain , so the Linux box does NAT for the Windows VM and for the
Android mobile clients, the laptop named instance serves authorative
zones for my localhost, local VMs and DMZ Android Mobile phone units,
and ALL hosts, including the windows host, use BIND named running
on the Linux laptop gateway, which is the default route endpoint
for all hosts, and which has a 'forwarders { ... };' clause in
named.conf containing my Cellular Network provider's DNS server IP
addresses . These remote Cellular DNS servers can respond very slowly at peak
internet usage times. It is nice to be able to see all packets from the
android mobile phones with tcpdump, and to be able to receive
the voice traffic that they send to our cloud SIP server
(which I can see being NAT-ed), and the SIP server sends
back, which get NAT-ed to the Windows VM Dispatcher and
audio playback GUI running on the laptop which I also maintain .
My BIND named server also implements an RBL blacklist kindly made available
as a hosts file, which I convert to a Response Policy Zone file,
at https://someonewhocares.org/hosts . DNSSEC is also enabled
by default.
My named.conf has a clause:
allow-query { localhost; 192.168.W.0/24; 192.168.M.0/24;
192.168.V.0/24;
};
where W is Windows VM network, M is mobile device network,
and V is my corporate L2TP/IPSEC VPN network, also doing NAT,
and one 'localhost-resolver' "View" with
match-clients { /* same as above */ } ;
and
recursion yes;
This setup works great on a normal office LAN , where there
are multiple hops to the internet available, but not on my
home slow single ethernet connection to the whole ethernet,
through a modem that must peridically renegotiate a DHCP lease.
When the modem renegotiates its DHCP lease every hour, I typically
have to restart named and hostapd .
I just want named to notice that the response times to
the forwarders are increasing , and to increase its
number of UDP re-transmit attempts and timeout time (time
between attempts ) accordingly, and vice versa
(decrease them back to defaults when forwarder responsiveness
improves).
Before I start hacking the named udp.c server code , please
could anyone advise if there are ways through configuration
settings to adjust the named UDP re-transmit timeout & number
of attempts strategy for slow networks ?
I can't believe there aren't any ?
Thanks in advance for any informative replies,
Best Regards,
Jason Vas Dias