Opened 18 months ago

Last modified 18 months ago

#22976 new defect

busybox: ntpd uses wrong IPv6 address in reply to query

Reported by: hellfire@… Owned by: developers
Priority: normal Milestone: Designated Driver (Trunk)
Component: packages Version: Trunk
Keywords: Cc:


I have a couple of routers that I'm using in a mesh setup with BMX6 and an OpenVPN tunnel over the top, the routers have no RTC and rely on ntp to sync the time after BMX6 is initialized but before the VPN is set up.

Router 1 is configured with three IPv6 addresses. The link local fe80:: address, the fd66:66:66:: BMX6 address, and a private (ie.) fd2e::/64 address.

Router 2 only has two, the link local, and the BMX6 fd66:66:66:: address.

Private address fd2e:: is advertised out to the mesh with BMX6. Routers have three services that run directly on the mesh interface, BMX6, NTP and OpenVPN.

Router 2 boots up, ifups wlan0 adhoc onto the mesh network, BMX6 allocates an address and gets the advertised network from Router 1. Router 2 then sends an NTP request off to the advertised network from Router 1 (to fd2e:: address). Router 1 (running busybox ntpd) replies with the source address set to fd66:66:66:: address, and router 2 drops it because it's coming back from the wrong address.

I'm assuming that busybox ntpd on router 1 looks up the source address from the interface based on the route to router 2 is the fd66:66:66:: address and uses that, but it's not the correct source address.

ISC ntpd as a replacement responds from the correct IP as expected, and I am using it in place of busybox, at a hit of 3 times the memory usage.

If required, I can recreate the conditions of this test with tcpdump outputs.

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Change History (1)

comment:1 Changed 18 months ago by stintel

The same problem occurs with IPv4, see #18404. I suggest to close this as a dupe, and I reported this problem upstream.

Last edited 18 months ago by stintel (previous) (diff)

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