szatox
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Joined: 27 Aug 2013
Posts: 3498
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 Posted: Sat Feb 08, 2025 3:55 pm Post subject: MPTCP on RPI4B with armbian + patched rpi-sources |
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Long story short, I wanted to enable MPTCP on my RPI4B with armbian.
I've been using it successfully on AMD64 via a kernel patch that attempts to upgrade all TCP sockets to MPTCP. If MPTCP is not supported by the remote end, kernel automagically fails back to TCP anyway, so there is no harm carpet-bombing it like that. Anyway, I though it would be a good idea to apply the same patch to my rpi. post 8826211
I crosscompiled raspberrypi-sources according to https://www.raspberrypi.com/documentation/computers/linux_kernel.html and transplanted it into previously installed armbian I've been using for a while. It boots, services work, I even recompiled an out-of-tree wifi module to get a USB dongle back. So far so good... But mptcp doesn't work.
Tried again with IPv6 permanently built into kernel instead of as a module, enabled MPTCP for IPv6, and it still doesn't activate.
The only difference compared to earlier is that when I ssh to it from a laptop where MPTCP actually works, I see 2 of those lines instead of 1:
| Quote: | | setsockopt socket 3 IPV6_TCLASS 72: Operation not supported |
It still connects though.
Connecting via ipv4 doesn't print any errors at all. In either case, the session does not transfer between ethernet and wifi like expected (It does work with my VPS; I can switch between wifi and a cellphone modem without dropping SSH session; RPI has multiple interfaces and VPS only 1, but AFAIK it shouldn't matter)
There are no firewalls, independently of each other both links work, it's just not using multipath.
| Code: | rpi # sysctl -a | grep mptcp
net.ipv4.tcp_available_ulp = mptcp
net.mptcp.add_addr_timeout = 120
net.mptcp.allow_join_initial_addr_port = 1
net.mptcp.checksum_enabled = 0
net.mptcp.enabled = 1
net.mptcp.pm_type = 0
net.mptcp.scheduler = default
net.mptcp.stale_loss_cnt = 4
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| Code: | laptop # sysctl -a | grep mptcp
net.ipv4.tcp_available_ulp = mptcp
net.mptcp.add_addr_timeout = 120
net.mptcp.allow_join_initial_addr_port = 1
net.mptcp.available_schedulers = default
net.mptcp.blackhole_timeout = 3600
net.mptcp.checksum_enabled = 0
net.mptcp.close_timeout = 60
net.mptcp.enabled = 1
net.mptcp.pm_type = 0
net.mptcp.scheduler = default
net.mptcp.stale_loss_cnt = 4
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So, any ideas?
Edit: I snooped on the traffic with Wireshark, it does recognize the conversation as an MPTCP stream, however there is only 1 substream with index 0. I'm pretty sure endpoints should advertise their other IPs, so maybe I need to play with routing rules a bit to get them to advertise the other IPs....
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