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I have been trying to set up my NTP server for both IPv4 and IPv6. IPv4 is working fine, as are other TCP and UDP services configured on IPv6, but I cannot get my NTP server to respond to IPv6 queries and I don't understand why.

NTP server is ntpsec 1.2.2 (shipped with Ubuntu 24.04), settings:

driftfile /var/lib/ntpsec/ntp.drift leapfile /usr/share/zoneinfo/leap-seconds.list tos maxclock 11 tos minclock 4 minsane 3 interface listen (my LAN ipv4 address) interface listen 2a01:0261:0e4a:cb::2 pool ntp.t-2.net pool 3.ubuntu.pool.ntp.org restrict -4 default kod nomodify nopeer noquery limited restrict -6 default kod nomodify nopeer noquery limited restrict 127.0.0.1 restrict ::1

Netstat shows it listening on IPv6 wildcard:

# netstat -tunpl | grep ntp udp 0 0 (my lan ip):123 0.0.0.0:* 54219/ntpd udp 0 0 127.0.0.1:123 0.0.0.0:* 54219/ntpd udp 0 0 0.0.0.0:123 0.0.0.0:* 54219/ntpd udp6 0 0 ::1:123 :::* 54219/ntpd udp6 0 0 :::123 :::* 54219/ntpd

ntpdate (from behind the router) shows data transmission:

# ntpdate -d -6 2a01:261:e4a:cb00::2 3 Jun 21:24:32 ntpdate[11496]: ntpdate [email protected] (1) Looking for host 2a01:261:e4a:cb00::2 and service ntp 2a01:261:e4a:cb00::2 reversed to m2.lan host found : m2.lan transmit(2a01:261:e4a:cb00::2) transmit(2a01:261:e4a:cb00::2) transmit(2a01:261:e4a:cb00::2) transmit(2a01:261:e4a:cb00::2) 2a01:261:e4a:cb00::2: Server dropped: no data

tcpdump shows data received, but no responses:

# tcpdump -i enp42s0 udp port 123 and ip6 tcpdump: verbose output suppressed, use -v[v]... for full protocol decode listening on enp42s0, link-type EN10MB (Ethernet), snapshot length 262144 bytes 19:24:32.801627 IP6 2a01:261:e4a:cb00:lanipv6.51439 > m2.lan.ntp: NTPv4, Client, length 48 19:24:34.801528 IP6 2a01:261:e4a:cb00:lanipv6.51439 > m2.lan.ntp: NTPv4, Client, length 48 19:24:36.801207 IP6 2a01:261:e4a:cb00:lanipv6.51439 > m2.lan.ntp: NTPv4, Client, length 48 19:24:38.801200 IP6 2a01:261:e4a:cb00:lanipv6.51439 > m2.lan.ntp: NTPv4, Client, length 48

IPv6 networking is configured using DHCP and as mentioned other services like DNS work just fine over both TCP and UDP, so I assume the routing is set up correctly.

Where's the catch?

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  • Firewall? ..... Commented Jun 3, 2024 at 20:35
  • UFW is inactive. I also tried disabling the UFW service and it's behaving the same as before. Commented Jun 3, 2024 at 20:38

1 Answer 1

Reset to default
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Your interface listen doesn't match your test address: 2a01:0261:0e4a:cb::2 is equivalent to 2a01:0261:0e4a:00cb::2, not 2a01:0261:0e4a:cb00::2.

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