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jonnybarnes

Member

From: Manchester, UK

Registered: 2011-05-11

Posts: 129

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Delay in IPv6 lookup when using ping

If I have an uncached domain ping hangs for a while before showing the PING line, but if the result is cached everthing happens quickly.

I’m using systemd-networkd and systemd-resolved with /etc/resolve.conf symlinking to the resolved stub.

$ time ping -6 -c 4 ipv6.com
PING ipv6.com(2604:7c00:18:e::2 (2604:7c00:18:e::2)) 56 data bytes
64 bytes from 2604:7c00:18:e::2 (2604:7c00:18:e::2): icmp_seq=1 ttl=51 time=94.5 ms
64 bytes from 2604:7c00:18:e::2 (2604:7c00:18:e::2): icmp_seq=2 ttl=51 time=94.7 ms
64 bytes from 2604:7c00:18:e::2 (2604:7c00:18:e::2): icmp_seq=3 ttl=51 time=94.5 ms
64 bytes from 2604:7c00:18:e::2 (2604:7c00:18:e::2): icmp_seq=4 ttl=51 time=94.7 ms

--- ipv6.com ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3003ms
rtt min/avg/max/mdev = 94.492/94.621/94.742/0.112 ms
ping -6 -c 4 ipv6.com  0.00s user 0.00s system 0% cpu 20.167 total

$ time ping -6 -c 4 ipv6.com
PING ipv6.com(2604:7c00:18:e::2 (2604:7c00:18:e::2)) 56 data bytes
64 bytes from 2604:7c00:18:e::2 (2604:7c00:18:e::2): icmp_seq=1 ttl=51 time=94.6 ms
64 bytes from 2604:7c00:18:e::2 (2604:7c00:18:e::2): icmp_seq=2 ttl=51 time=94.5 ms
64 bytes from 2604:7c00:18:e::2 (2604:7c00:18:e::2): icmp_seq=3 ttl=51 time=94.6 ms
64 bytes from 2604:7c00:18:e::2 (2604:7c00:18:e::2): icmp_seq=4 ttl=51 time=94.5 ms

--- ipv6.com ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3004ms
rtt min/avg/max/mdev = 94.487/94.530/94.565/0.029 ms
ping -6 -c 4 ipv6.com  0.01s user 0.00s system 0% cpu 3.241 total

I don’t notice any delays when making ping use IPv4.

It also seems specific to ping. Using curl I notice no IPv6 delays.

Last edited by jonnybarnes (2020-08-22 15:26:38)