[Dnsmasq-discuss] Quicker IPv6 connectivity recovery when using ra-stateless mode

[Toke Høiland-Jørgensen]

So I've been noticing that when resuming my laptop from suspend (and
reconnecting to the WiFi network), I will get IPv4 connectivity a lot
sooner than IPv6. I'm using dnsmasq in ra-stateless mode.

Looking at tcpdump output, it seems that my laptop will send a DHCP
solicit message (for both IPv4 and IPv6) immediately when the interface
connects to the WiFi, and it does get an IPv6 reply from dnsmasq. But it
takes a while before a router advertisement arrives, so there will be no
default route installed on the laptop.

Provided I'm interpreting what is happening correctly, would it be
possible to have dnsmasq trigger a router advertisement on an interface
whenever it replies to DHCP requests? Not sure if the RA spec allows
unicasting advertisements; if it does, unicasting it to the host that
asks for DHCP would be a way to cut down on multicast traffic. But
simply sending an additional multicast RA would also work, I suppose.

-Toke

[Xander Victory]

Post by Toke Høiland-Jørgensen
So I've been noticing that when resuming my laptop from suspend (and
reconnecting to the WiFi network), I will get IPv4 connectivity a lot
sooner than IPv6. I'm using dnsmasq in ra-stateless mode.
Looking at tcpdump output, it seems that my laptop will send a DHCP
solicit message (for both IPv4 and IPv6) immediately when the interface
connects to the WiFi, and it does get an IPv6 reply from dnsmasq. But it
takes a while before a router advertisement arrives, so there will be no
default route installed on the laptop.
Provided I'm interpreting what is happening correctly, would it be
possible to have dnsmasq trigger a router advertisement on an interface
whenever it replies to DHCP requests? Not sure if the RA spec allows
unicasting advertisements; if it does, unicasting it to the host that
asks for DHCP would be a way to cut down on multicast traffic. But
simply sending an additional multicast RA would also work, I suppose.
-Toke
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You laptop should send an ipv6 router solicit (which should trigger an
advertisement). Do you see this looking at tcpdump for icmpv6?
What OS & version is it running?

[Toke Høiland-Jørgensen]

Post by Xander Victory
You laptop should send an ipv6 router solicit (which should trigger an
advertisement). Do you see this looking at tcpdump for icmpv6?
What OS & version is it running?

Ah, I see. No, my laptop doesn't seem to be sending router solicitation
messages, even though the relevant sysctls are set to their default
values. I'm running Arch Linux on kernel 4.6.4, using systemd-networkd
to configure the interface.

It may be that there's some timing issues with the connection not being
available even though the interface appears to be up from the kernel's
point of view. Haven't been able to see any router solicitations go out
at all, though.

Aha, and there appears to be a systemd bug opened on this:
https://github.com/systemd/systemd/issues/3664 -- will investigate
further... thanks for the pointer :)

-Toke