[Dnsmasq-discuss] IPv6 Router Advertisements eating a CPU Core + Constantly being Multicasted

Cooper Lees me at cooperlees.com
Mon Aug 5 14:44:56 BST 2019 

Hi,

Many thanks for your suggestions.

Maybe I was not clear enough. With `dhcp-range=2601:647:4d01:fbf::,ra-names` in the config causes 'top' to show a lot of CPU used (>90%):
```
19492 dnsmasq   20   0   11076   2536   2228 R  93.4   0.1 815:27.43 /usr/sbin/dnsmasq -x /run/dnsmasq/dnsmasq.pid -u dnsmasq -r /run/dnsmasq/resolv.conf -7 /etc/dnsmasq.d,.dpkg-dist,.dpkg-old,.dpkg-new --local-service
```
AND tcpdump shows a barrage of RAs being advertised:
```
06:39:00.390680 IP6 fe80::dea6:32ff:fe02:b43d > ff02::1: ICMP6, router advertisement, length 88
06:39:00.391455 IP6 fe80::dea6:32ff:fe02:b43d > ff02::1: ICMP6, router advertisement, length 88
06:39:00.392017 IP6 fe80::dea6:32ff:fe02:b43d > ff02::1: ICMP6, router advertisement, length 88
06:39:00.392564 IP6 fe80::dea6:32ff:fe02:b43d > ff02::1: ICMP6, router advertisement, length 88
06:39:00.393103 IP6 fe80::dea6:32ff:fe02:b43d > ff02::1: ICMP6, router advertisement, length 88
```
- Please look at the timestamps here
- Milliseconds apart 

I've replied to everything else in line. I guess it's going to be time to dig into the source code here if nothing else in my config looks outside the ordinary.

Cheers,
Cooper

> On Aug 4, 2019, at 11:29 PM, Geert Stappers <stappers at stappers.nl> wrote:
> 
> On Sun, Aug 04, 2019 at 03:05:45PM -0700, Cooper Lees wrote:
>> Hello,
>> 
>> I'm running dnsmasq 2.80 on a Raspberry PI and when I enable IPv6
>> Router Advertisements on even one interface the CPU usage pins a
>> core with continually advertising RAs. Logs and tcpdump confirm it's
>> something to do with enabling IPv6 RAs / SLAAC on an interface (when
>> I remove CPU goes right back down to where I'd imagine this daemon to
>> be on a ~10 node home network). I've tried to tune the advertisement
>> to every 4 seconds, but it seems to have no effect. I've also tried
>> TRUNK/HEAD and it reproduces with my config. I've added the options +
>> config used below to help provide a reproducible setup.
>> 
>> Any suggestions I could try / do or is this indeed a bug with dnsmasq?
>> 
>> ./src/dnsmasq -x /run/dnsmasq/dnsmasq.pid -u dnsmasq -r /run/dnsmasq/resolv.conf -7 /etc/dnsmasq.d,.dpkg-dist,.dpkg-old,.dpkg-new --local-service
> 
> The    `,.dpkg-dist,.dpkg-old,.dpkg-new` somewhat odd.
> Probably a side effect of some wildcard expansion.
> 
> Check what is inside those  .dpkg-distl.dpkg-old .dpkg-new files.
> Remove them if there is nothing usefull in. And surely remove
> them when there is only duplicate configuration.

This seems to be a default with the raspbian install - There is nothing in /etc/dnsmasq.d
```
cooper at home:~ $ find /etc/dnsmasq.d
/etc/dnsmasq.d
/etc/dnsmasq.d/README
```

Removing these and running the daemon has no effect.
```
31737 dnsmasq   20   0    2244    120      0 R  85.8   0.0   0:15.87 ./src/dnsmasq -x /run/dnsmasq/dnsmasq.pid -u dnsmasq -r /run/dnsmasq/resolv.conf --local-service
```

> 
> 
>> ```
>> Log from starting with HEAD:
>> Aug  4 14:44:30 home dnsmasq[19340]: started, version 2.80-58-g3052ce2 cachesize 150
>> Aug  4 14:44:30 home dnsmasq[19340]: compile time options: IPv6 GNU-getopt no-DBus no-UBus no-i18n no-IDN DHCP DHCPv6 no-Lua TFTP no-conntrack ipset auth no-DNSSEC loop-detect inotify dumpfile
>> Aug  4 14:44:30 home dnsmasq-dhcp[19340]: DHCP, IP range 10.6.9.10 -- 10.6.9.200, lease time 1d
>> Aug  4 14:44:30 home dnsmasq-dhcp[19340]: DHCP, IP range 192.168.107.10 -- 192.168.107.100, lease time 1h
>> Aug  4 14:44:30 home dnsmasq-dhcp[19340]: DHCPv4-derived IPv6 names on 2601:647:4d01:fbf::
>> Aug  4 14:44:30 home dnsmasq-dhcp[19340]: router advertisement on 2601:647:4d01:fbf::
>> Aug  4 14:44:30 home dnsmasq[19340]: reading /run/dnsmasq/resolv.conf
>> Aug  4 14:44:30 home dnsmasq[19340]: using nameserver 75.75.75.75#53
>> Aug  4 14:44:30 home dnsmasq[19340]: using nameserver 75.75.76.76#53
>> Aug  4 14:44:30 home dnsmasq[19340]: read /etc/hosts - 6 addresses
>> Aug  4 14:44:30 home dnsmasq-dhcp[19340]: SLAAC-CONFIRM(eth0.69) 2601:647:4d01:fbf:fea1:83ff:fe5e:d592 amazon-057c5fa7e
>> Aug  4 14:44:30 home dnsmasq-dhcp[19340]: SLAAC-CONFIRM(eth0.69) 2601:647:4d01:fbf:36d2:70ff:feb1:f402 amazon-9ad27ed72
>> Aug  4 14:44:30 home dnsmasq-dhcp[19340]: SLAAC-CONFIRM(eth0.69) 2601:647:4d01:fbf:8a71:e5ff:fedb:b5e6 amazon-77495bfb3
>> Aug  4 14:44:30 home dnsmasq-dhcp[19340]: DHCPDISCOVER(eth0.69) dc:a2:66:59:6d:1f
>> Aug  4 14:44:30 home dnsmasq-dhcp[19340]: DHCPOFFER(eth0.69) 10.6.9.189 dc:a2:66:59:6d:1f
>> Aug  4 14:44:30 home dnsmasq-dhcp[19340]: DHCPREQUEST(eth0.69) 10.6.9.189 dc:a2:66:59:6d:1f
>> Aug  4 14:44:30 home dnsmasq-dhcp[19340]: DHCPACK(eth0.69) 10.6.9.189 dc:a2:66:59:6d:1f
>> ```
> 
> Nothing that indicates a 25% CPU load.
- This is because I added the `quiet-ra` option 
- Otherwise it's just 10000s `dnsmasq-dhcp[19424]: RTR-ADVERT(eth0.69) 2601:647:4d01:fbf::` lines in logs

> 
>> 
>> Log Messages (without quiet-ra)
>> ```
>> Aug  4 14:52:30 home dnsmasq-dhcp[19424]: RTR-ADVERT(eth0.69) 2601:647:4d01:fbf::
>> ```
> 
> Even less
> 
> Previously
>> core with continually advertising RAs. Logs and tcpdump confirm it's
> 
> Without flooding this mailinglist,
> please share somehow that data with us.
> 
> 
> 
>> Config:
>> ```
>> # Never forward plain names (without a dot or domain part)
>> bogus-priv
>> # Never forward addresses in the non-routed address spaces.
>> domain-needed
>> 
>> # Delays sending DHCPOFFER and proxydhcp replies for at least the specified number of seconds.
>> dhcp-mac=set:client_is_a_pi,B8:27:EB:*:*:*
>> dhcp-reply-delay=tag:client_is_a_pi,2
> 
> Why that delay?
> What is the effect of removing it?
- This is a default in the raspbian dnsmasq install
- Removing this has no effect
> 
> 
>> # List of all the interfaces for dnsmasq to listen on
>> # Sample interface line: interface=eth0
>> interface=eth0
>> interface=eth0.69
>> 
>> # v4 - manually set these options
>> dhcp-option=option:domain-search,cooperlees.com
>> dhcp-option=option:router,10.6.9.2
>> dhcp-range=eth0,192.168.107.10,192.168.107.100,1h
>> dhcp-range=eth0.69,10.6.9.10,10.6.9.200,24h
>> 
>> 
>> # v6 Sateless RA + Names
>> # Sample DHCP range line: dhcp-range=2601:647:4d01:fbf::, ra-stateless, ra-names
>> #dhcp-range=2601:647:4d01:fbf::,ra-stateless, ra-names
>> dhcp-range=2601:647:4d01:fbf::,ra-names
>> #ra-param=eth0.69,4
>> quiet-ra
>> ```
>> 
>> Thanks,
>> Cooper
> 
> Please keep us, this mailinglist, informed.
> 
> After all is a unknow bug far worse then ten known bugs.
>> Any suggestions I could try / do or is this indeed a bug with dnsmasq?
> 
> 
> 
> Groeten
> Geert Stappers
> -- 
> Leven en laten leven
> 
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