Unbound DNS Error - Send failed: No buffer space available

[panda39]

I was having this issue since 25.5 and now I'm at 26.1. I've had to keep restarting OPNSense just so I can update to 26.1.10. I've increased the the tunable "kern.ipc.maxsockbuf" to 10MB as I've seen in a previous post before.

I don't have any VPNs configured, yet. I have a separate internal DNS server that I use for internal network. I only use Unbound for OPNSense. I've tried pointing system to my Internal DNS server and that works, but I really want to use Unbound only for OPNSense, but I don't know what else could be wrong.

[deajan]

Seeing the same issue here with OPNsense 26.1.11_6-amd64 (but agreed, this happens since a months or two for me).


I noticed that the Unbound logs are full of the following logs:
```
2026-07-09T00:10:21Noticeunbound[57596:0] notice: send failed: No buffer space available
2026-07-09T00:10:20Noticeunbound[57596:4] notice: remote address is 9.9.9.9 port 53
2026-07-09T00:10:20Noticeunbound[57596:4] notice: send failed: No buffer space available
2026-07-09T00:10:20Noticeunbound[57596:5] notice: remote address is 9.9.9.9 port 53
2026-07-09T00:10:20Noticeunbound[57596:5] notice: send failed: No buffer space available
2026-07-09T00:10:20Noticeunbound[57596:2] notice: remote address is 9.9.9.9 port 53
2026-07-09T00:10:20Noticeunbound[57596:2] notice: send failed: No buffer space available
2026-07-09T00:10:20Noticeunbound[57596:3] notice: remote address is 9.9.9.9 port 53
```

Firewall is quite used:
```
memory
- states: 3067500
- src-nodes: 3067500
- frags: 5000
- table-entries: 8000000
```
As for the suggested sysctl value, I have the default setting `kern.ipc.maxsockbuf: 4262144` for now.

I'm running WAN + LAN on a lagg interface with VLANs. Physical cards are Ethernet Controller X710 for 10GbE SFP+.
Also running Zenarmor (physical interface via L3 netmap native driver) + Suricata (on WAN links) and crowdsec.
I'm wondering whether the above three are compatible with each other.

Since I use 9.9.9.9 as gateway monitor IP for one of my WAN links, I switched unbound forwarder IP 9.9.9.9 to 8.8.4.4 in order to outrule too much traffic to that DNS resolver. Let's see.