Strange Networking Issue on Manjaro ARM

[kayako]

It appears I cannot post on the ARM board, and the issue seems not really that related to the ARM architecture itself, so I’m posting it here.

Summary: odd packet loss between kernel space and userland

Longer background:
I’m using WireGuard to connect to the Internet, but I leave some applications connected directly to the network (not via WG). Quite standard routing stuff, right? Here’s how I always did this:

Table = off
PostUp = ip -4 route add default dev %i via VPN_GATEWAY_V4 table 64; ip -6 route add default dev %i via VPN_GATEWAY_V6 metric 0 table 64; ip rule add uidrange 1000-1000 table 64; ip -6 rule add uidrange 1000-1000 table 64
PreDown = ip -4 route del default dev %i via VPN_GATEWAY_V4 table 64; ip -6 route del default dev %i via VPN_GATEWAY_V6 metric 0 table 64; ip rule del uidrange 1000-1000 table 64; ip -6 rule del uidrange 1000-1000 table 64

I’ve tested this on Ubuntu x86_64, Arch x86_64, Raspberry Pi OS, and Arch ARM (sorry I do not have a spare machine for Manjaro x86_64 right now). It worked well everywhere until I did exactly the same on Manjaro ARM (dev build from GitHub - manjaro-arm/rpi4-images since I’m using Raspberry Pi 5).

The problem is, that while IPv4 works, IPv6 (TCP, UDP, ICMP) connections never receive responses. I then did some tests to find out what was going on, and tcpdump clearly told me response packets are received:

wg0   Out IP6 pi > dns.google: ICMP6, echo request, id 17, seq 7, length 64
wg0   In  IP6 dns.google > pi: ICMP6, echo reply, id 17, seq 7, length 64

But, the received packets never made their way to the userland. Timeout, timeout, timeout. strace indicated that the read operation failed:

sendto(4, "\200\0\0\0\377\377\0\2\323\"[e\0\0\0\0\221\260\n\0\0\0\0\0\20\21\22\23\24\25\26\27"..., 64, 0, {sa_family=AF_INET6, sin6_port=htons(58), sin6_flowinfo=htonl(0), inet_pton(AF_INET6, "2001:4860:4860::8888", &sin6_addr), sin6_scope_id=0}, 28) = 64
recvmsg(4, {msg_namelen=128}, 0)        = -1 EAGAIN (Resource temporarily unavailable)

So, the issue lies in the kernel space, which is really out of my expertise. Has anyone seen similar issues before? Any kind of help or hint is highly appreciated. Thanks.

[Darksky]

It has been a long time since I set mine up and really do not understand what all you are trying to do but I had to do this here in one of my steps.

/etc/sysctl.conf

net.ipv6.ip_forward=1

[kayako]

Thank you for your reply. I’m doing split view VPN: some system accounts use VPN while others don’t.

There is no “net.ipv6.ip_forward=1” but there are “net.ipv6.conf.all.forwarding = 1” and similar options. However enabling them does not fix the issue. I also tried installing the kernel from Arch Linux ARM, still no luck. But what I can confirm is on Arch Linux ARM this works. Weird.

[kayako]

I just solved the problem: it might have something to do with NetworkManager, not the kernel or Manjaro. Installing a minimal version of Manjaro fixed the issue.