illumos subnet router doesn't route ICMP pings

[nshalman]

What is the issue?

My tailnet has two subnet routers, one that runs on a raspberry pi running linux, the other in an illumos zone.
If I disable the illumos one and enable the pi, my phone can ping an IP in the LAN subnet from outside the house.
If I disable the pi and enable the illumos one, my phone cannot ping that IP on the LAN (it can still do e.g. TCP just fine)

Also reported by a user on IRC.

Steps to reproduce

Create an illumos subnet router advertising a subnet
try to ping an IP on the other side of the subnet router

Are there any recent changes that introduced the issue?

No response

OS

Other

OS version

illumos

Tailscale version

1.80.2-sunos

Other software

No response

Bug report

No response

[extrowerk]

Ping.

[extrowerk]

I have installed my NAs in december, and I am sure I had ping working, so I have tested all release back to that date, but none works.
Any other idea?

[extrowerk]

Tested with v1.80.3-sunos, still not working.

[extrowerk]

Tested with v1.82.0, still not ok.