[Dnsmasq-discuss] IPv6 Router Advertisement not advertising.

[John Gorkos]

Dnsmasq gurus-

I¹m running dnsmasq version 2.67 on my Debian ³jessie² edge router.  I¹m on
a Comcast residential cable connection on eth0 with full dual-stack
IPv4/IPv6.  When I run radvd, I get router advertisements for my subnet (as
assigned by Comcast via dhcp6), and all of my internal *Nix boxes (about 15)
all get SLAAC addresses and are able to route IPv6 packets to the world.
So, I know IPv6 works, and I know I can route and do DNS lookups.

I¹d like to replace radvd with DNSMasq, since I use dnsmasq for ipv4 DHCP
and DNS queries.  Here is the relevant section of my dnsmasq.conf:
#dhcp-authoritative
dhcp-leasefile=/tmp/dhcp.leases
dhcp-range=trusted,192.168.5.2,192.168.5.100,1h
enable-ra
dhcp-range=::1,::400,constructor:eth1, slaac,ra-only
ra-param=eth1,high,5

And here¹s what it looks like in the logs when it starts:
Nov 22 13:52:44 dnsmasq[27279]: started, version 2.67 cachesize 150
Nov 22 13:52:44 dnsmasq[27279]: compile time options: IPv6 GNU-getopt DBus
i18n IDN DHCP DHCPv6 no-Lua TFTP conntrack ipset auth
Nov 22 13:52:44 dnsmasq-dhcp[27279]: DHCP, IP range 192.168.5.2 --
192.168.5.100, lease time 1h
Nov 22 13:52:44 dnsmasq-dhcp[27279]: DHCPv6, IP range ::1 -- ::400, lease
time 1h, template for eth1
Nov 22 13:52:44 dnsmasq-dhcp[27279]: router advertisement on eth1
Nov 22 13:52:44 dnsmasq-dhcp[27279]: DHCPv6, IP range 2601:0:XXXX:XXXX::1 --
2601:0:XXXX:XXXX::400, lease time 1h, constructed for eth1
Nov 22 13:52:44 dnsmasq-dhcp[27279]: router advertisement on
2601:0:b580:44c::, constructed for eth1
Nov 22 13:52:44 dnsmasq-dhcp[27279]: IPv6 router advertisement enabled
Nov 22 13:52:44 dnsmasq[27279]: using nameserver 8.8.8.8#53
Nov 22 13:52:44 dnsmasq[27279]: using nameserver 75.75.75.75#53
Nov 22 13:52:44 dnsmasq[27279]: using local addresses only for domain lan
Nov 22 13:52:44 dnsmasq[27279]: read /etc/hosts - 86 addresses

However, running TCP dump like so:
tcpdump -s0 -n -i eth1 'icmp6 and ((ip6[40+0] == 133) or (ip6[40+0] ==
134))¹
I NEVER see router advertisements.  Switching back to radvd, I see this:
13:49:57.622991 IP6 fe80::e2cb:4eff:fe79:e057 > ff02::1: ICMP6, router
advertisement, length 48
13:50:05.582248 IP6 fe80::e2cb:4eff:fe79:e057 > ff02::1: ICMP6, router
advertisement, length 48

Those IPv6 addresses are the link-local address of my eth1 card (internal
network).  With dnsmasq, I never see an advertisement, my clients don¹t get
IPv6 addresses, and those that already have them fail to route.  Running
radvd, everything just works.

I¹m sure I¹m doing something silly/stupid, but I¹m unsure what.  I¹ll be
happy to provide additional information, either on or off list.

Thank you.
John Gorkos



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