Dnsmasq very chatty

jow · June 18, 2019, 10:14am

Mainly because dnsmasq does not allow for dynamic IPv6 prefix management. You either need to let it handle everything autonomously, breaking many system integrations or you have to frequently pregenerate updated configs for it and restart the process, leading to a loss of state.

mbo2o · June 18, 2019, 10:21am

https://openwrt.org/docs/guide-user/base-system/dhcp

options for dhcp sections.

Name: `dhcpv6`
Type:
string
Required:
no
Default:
(none)

Description: 
Specifies whether DHCPv6 server should be enabled ( `server` ), relayed ( `relay` ) or disabled ( `disabled` )

supersebbo · June 18, 2019, 10:36am

So if you use odhcp for all DHCP, do you lose any integrations/functionality (other than NTP advertisements as noted by @anon45274024).

anon45274024 · June 18, 2019, 11:00am

just as general note on cluttered system logs I am using syslog-ng to filter out from the main log whatever I want out of it, e.g.

filter {
  		not (facility(kern) and match("DROP" value("MESSAGE")));
  		not (program(sshd) or program(cron) or  program(odhcpd) or program(dnsmasq));
  	};

and get it written into separate logs files (that are not conveniently accessible via LuCI though but only through ssh file browser). Maybe one day there will be a LuCI file browser

eduperez · June 18, 2019, 11:13am

I looked again, and I do have that section, too... sorry. I even have the same trigger option there.

What I can confirm is that I do not see those messages on the logs.

richb-hanover-priv · June 19, 2019, 11:42am

@WiteWulf, @supersebbo, This is slightly OT, but in fact very relevant to that long-duration open bug report. Simon Kelley (author of dnsmasq) has worked solo to build the package across all sorts of devices, architectures, kernels, etc. His work is not funded by anyone, he's working very hard, and he's making decisions about where to focus.

Eric Raymond (esr) had started a social network to provide funding to those "Load Bearing Internet People". He discusses it in his blog posting Loadsharers: Funding the Load Bearing Internet People Consider funding some of the people on his list (like Simon). Thanks.

supersebbo · June 19, 2019, 12:49pm

Absolutely respect his work and it wasn't a dig at him. In fact this 'bug', as noted above, is nothing to do with dnsmasq, rather the OpenWRT default config of using two different DHCP servers side by side.

richb-hanover-priv · June 19, 2019, 1:02pm

I agree, and wasn't criticizing. I just wanted to publicize the Loadsharers so people like Simon might get support. (I'll put a longer stand-alone note on the Forum soon...) Thank you.

anon45274024 · June 19, 2019, 1:06pm

github.com/openwrt/openwrt

FS#2328 - Allocate resources to sort out odhcpd/dnsmasq interaction once and for all.

opened 11:31AM - 18 Jun 19 UTC

openwrt-bot

flyspray

*ldir:* As IPv6 is being adopted, increasingly people are seeing dnsmasq log 's…pam'. See https://bugs.openwrt.org/index.php?do=details&task_id=1492&string=1492&search_name=&type%5B0%5D=&sev%5B0%5D=&pri%5B0%5D=&due%5B0%5D=&reported%5B0%5D=&cat%5B0%5D=&status%5B0%5D=open&percent%5B0%5D=&opened=&dev=&closed=&duedatefrom=&duedateto=&changedfrom=&changedto=&openedfrom=&openedto=&closedfrom=&closedto= By default under openwrt, dhcpv4 leases are handled by dnsmasq whilst dhcpv6/RA is handled by openwrt's odhcpd. odhcpd could handle both v4 & v6 but does not yet have the same configuration flexibility for dhcp options as dnsmasq. I guess this is why no one has been brave enough to switch to odhcpd for ipv4 operations as well as ipv6. dnsmasq can also handle dhcpv6/RA but not quite as flexibly as odhcpd. dnsmasq will automatically find IP6 prefixes on interfaces and start handling them, whilst openwrt's strategy with odhcpd is to only handle stuff we tell you to handle, don't do it automagically. As dnsmasq is the default resolver for openwrt and the wider LAN, it needs to know about DHCP/hostname allocations. For DHCPv4 this is easy, dnsmasq is controlling them. For DHCPv6 a hosts file (called a statefile in the odhcpd code) is handed to dnsmasq. By default this host file is not read dynamically, so odhcpd has to signal dnsmasq to re-read the host file (and clear caches etc etc) upon every ipv6 lease change. This generates a lot of log spam and process startup overhead. There are also questions about service operability during this time. Effort needs to be put into sorting this out. Temporary workarounds: Use 'hostsdir' dnsmasq option instead of 'addn-hosts' - dnsmasq will dynamically scan changes/additions to hosts in hostsdir whereas addn-hosts needs a SIGHUP. Host deletions cannot be handled by this method, so odhcpd would still need to SIGHUP on lease expiry. It might reduce some of the spam. Longer term: Teach dnsmasq to accept hostname updates over an IPC mechanism. ubus? and carry on using odhcpd for ipv6. Teach dnsmasq to handle ipv6 prefix additions/deletions/handling via an IPC mechanism in the same way as odhcpd. Drop odhcpd and use dnsmasq for everything. Use odhcpd for everything and use another dns resolver that interfaces nicely with odhcpd. Why don't I see this problem: I use dnsmasq to handle ipv6 but I'm lucky enough that this works for me. This needs fixing/funding to sort it out though.

j.prince · August 17, 2019, 8:37am

For a simple home network would turning off IPv6 by disabling oducpd be OK?
Sorry if this is a really dumb question.

vgaetera · August 17, 2019, 9:01am

Why do you want to disable it?
In any case, you can't easily disable IPv6 LLA.

j.prince · August 17, 2019, 9:02am

I have a similar problem to that described above, lots of host reloads and a large(ish) adblock list that causes the router to have a little think and holding up traffic.