there's a networking issue affecting LNVPS instances that's blocking connectivity to several external hosts.
Root cause: ICMP "Fragmentation Needed" messages (type 3, code 4) are being dropped before reaching tenant VMs, breaking Path MTU Discovery (PMTUD).
Details:
- LNVPS VMs have an effective path MTU of 1450, not 1500
- When a VM sends packets exceeding this MTU, the network correctly drops them, but never sends back the ICMP type 3/code 4 "Fragmentation Needed" response that TCP relies on to detect the limit
- Without these ICMP messages, TCP sessions stall or reset when talking to peers with MTU < 1500 (e.g. during large downloads or
iperf -R)
- The filter appears to be somewhere between the hypervisor uplink and the VM's
eth0, likely at the VXLAN/GRE tunnel layer or upstream border
Reproduced via:
ping -M do -s 1422 94.156.119.69 → 4/4 received (within MTU)
ping -M do -s 1423 94.156.119.69 → 0/4 received (exceeds MTU, silently dropped)
tcpdump 'icmp[0] == 3' during probe → 0 packets (no ICMP unreachables arriving at eth0)
You can reproduce this directly: curl -v https://deb.debian.org/debian/extrafiles from any LNVPS machine will stall. apt on Debian is broken for the same reason.
Fix (either of):
- Allow ICMP type 3 code 4 through to tenant VMs
- Configure MSS clamping at the hypervisor level for all tenant VMs on this host
This is what's preventing OpenClaw instances from reaching LNemail, and many other places!