Re: [libvirt] [PATCHv2] handle DNS over IPv6

2011/1/6 Daniel P. Berrange <berrange(a)redhat.com&gt;: > 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)