Performance Tuning & Kernel Parameters (Sysctl)

Make your kernel stop being so paranoid about packet filtering

🧩 The Challenge

Dealing with a high-throughput load balancer only to find it randomly dropping packets is enough to make you pull your hair out. The kernel is often just being “too safe” for its own good by enabling reverse path filtering.

💡 The Fix

Flip the sysctl setting to disable strict reverse path filtering so your multi-homed box stops rejecting valid traffic that just happens to come in on a non-primary interface.

sysctl -w net.ipv4.conf.all.rp_filter=0
sysctl -w net.ipv4.conf.default.rp_filter=0

⚙️ Why It Works

Setting this to zero tells the kernel to stop checking if the source address of an incoming packet is reachable via the same interface it arrived on. And you really only want to do this if you actually understand your routing table, otherwise, you’re opening yourself up to IP spoofing headaches.

🚀 Pro-Tip: Don’t forget to push these into /etc/sysctl.conf unless you want to do it all over again after a reboot.

Linux Tips & Tricks | © ngelinux.com | 10/14/2026