Background:
I work with macOS and Windows. When accessing external servers via SSH from macOS, there are pauses of several seconds every few minutes during which the terminal freezes, but then continues to work normally afterward. I have since determined that this only happens with IPv6 connections. For example, if I use ssh -4 ssh.example.com, the problem does not occur. When using PuTTY on Windows from the same network, the issue also does not occur, regardless of whether IPv4 or IPv6 is used.
Switching to a different SSH client on macOS does not resolve the problem either.
Diagnosis so far:
The router is a FRITZ!Box running FRITZ!OS 8.25, Dual Stack internet connection. In its home network area, I noticed that several IPv6-LLAs (addresses starting with fe80::) — some of which are months old — are displayed for the macOS devices. Resetting the network connection for this device — or power-cycling the FRITZ!Box — seems to resolve the SSH issue (since the problem occurs sporadically, this isn’t 100% certain). However, the list of LLAs then starts to grow again.
It’s worth noting that the devices with multiple IPv6-LLA entries are running macOS and are connected to the home network via two network interfaces (LAN and Wi-Fi) simultaneously. It’s also worth noting that the LLAs in the FRITZ!Box are all assigned to the entry corresponding to the “en0” Ethernet interface on the respective Mac. This leads to the curious effect that an old Mac mini, which is connected only via Wi-Fi (“en1”), has no IPv6 LLA entry at all in the FRITZ!Box (though the LLA naturally already exists on the Mac mini itself).
Windows PCs, iPads, and iPhones, as well as other devices (NAS, Linux), each have exactly one LLA (as expected).
Questions:
Does anyone have a device that isn’t macOS-based and is also connected to a FRITZ!Box home network via two network interfaces? How are the IPv6 LLA entries in the FRITZ!Box distributed between the two interfaces in this case?
From a technical point of view, what are the consequences if the LLAs are assigned to the wrong interface? After all, actual communication with the Internet takes place via GUAs.
Is this more of a macOS issue or a FRITZ!OS issue?
