Short, frequent Internet drops with OpenWrt and Frontier

For whatever reason, I suddenly had intermittent ~2-3 minute long drops in internet a few times a day on my OpenWrt router. Connections inside my network worked fine (e.g. a ping from my computer to my router) but any connections out to the Internet did not (e.g. a ping from the router while connected to it via SSH to any website, or even the gateway). Using luci-app-statistics’s ping plugin, I was able to see spikes in the ICMP drop rate from the router to various servers and my gateway at the times of the drops.

For weeks, I tried many things for troubleshooting and hit many dead ends:

• Checking system logs on the OpenWrt router, but no relevant messages were outputted at the time of the drops
• Different Ethernet cables and ports
• Replacing the router with a new one, also running OpenWrt
• Many other settings changes in OpenWrt

However, while all this didn’t fix the issue, the Frontier-provided Eero worked fine, so it had to be related to OpenWrt instead of being on Frontier’s end.

Long story short, after many, many failed attempts, I eventually found the fix: I was able to set these values in the network device (eth1) associated with my wan interface (in LuCi, Network > Interfaces > Devices > Configure… > Advanced device options):

• Neighbor cache validity: 7200000 ms
• Stale neighbor cache timeout: 14400 s
• Minimum ARP validity time: 20 s

These values are much longer than the default. I’m not sure why this fixed it. Maybe there was new rate limiting on Frontier’s end related to ARP, but this was one of the stranger things I’ve had to troubleshoot.

This was months ago for me, but I’m leaving this here for either myself in the future or a possibly non-zero number of other people who encounter this.