Re: [libvirt] [PATCHv2] handle DNS over IPv6
2011/1/6 Daniel P. Berrange <berrange(a)redhat.com>:
While it is shorter to just use '--interface brname' this
comes
at the price of loosing compatibility with older dnsmasq which
we still wish to support.
sure. RHEL5 is important target :)
If we used '--listen-address $IPV4ADDR --listen-address
$IPV6ADDR'
then people with dnsmasq < 2.48 can still use the virtual network
capability in a IPv4 only context without problems. Only those
people who actually needed IPv6 DNS would have to upgrade to
newer dnsmasq.
hack for users of old dnsmasq and ipv6 needs is nodad option for
/sbin/ip tool - read below.
Do you have any idea what causes the delay ? In particular is
the delay caused by the use of --listen-interface, or caused
by the addition of IPv6 addrs ?
Delay is caused by DAD.
http://en.wikipedia.org/wiki/IPv6_address#Duplicate_address_detection
It's caused by IPv6 address, not by --listen-interface option:
# killall dnsmasq ; ip a del 2001:db8::1 dev wlan0 ; ip a add
2001:db8::1 dev wlan0 ; time dnsmasq --strict-order --bind-interfaces
--conf-file= --except-interface lo --listen-address 2001:db8::1
dnsmasq: no process killed
real 0m2.008s
user 0m0.000s
sys 0m0.006s
# killall dnsmasq ; ip a del 2001:db8::1 dev wlan0 ; ip a add
2001:db8::1 dev wlan0 ; time dnsmasq --strict-order --bind-interfaces
--conf-file= --except-interface lo --interface wlan0
real 0m2.006s
user 0m0.000s
sys 0m0.003s
We can add v6 address to interface with skipping DAD (nodad option for
/sbin/ip tool), but we can end up with duplicate v6 hosts on the same
network. Without DAD dnsmasq doesn't need to wait:
# killall dnsmasq ; ip a del 2001:db8::1 dev wlan0 ; ip a add
2001:db8::1 dev wlan0 nodad ; time dnsmasq --strict-order
--bind-interfaces --conf-file= --except-interface lo --interface
wlan0
dnsmasq: no process killed
real 0m0.017s
user 0m0.000s
sys 0m0.005s
Based on your descriptions here it sounds like going for multiple
--listen-address parameters offers the same level of overall
functionality, but with better compatibility for people on older
dnsmasq. So I'm not seeing a compelling reason to switch over to
using --listen-interface
OK, I understand.
Final question: what about link-local ipv6 addresses (fe80::/10).
Should we --listen-address on them? (I think we should)
--
Pawel