OpenWrt/LEDE Project

  • Status Unconfirmed
  • Percent Complete
  • Task Type Bug Report
  • Category Kernel
  • Assigned To No-one
  • Operating System All
  • Severity Low
  • Priority Very Low
  • Reported Version openwrt-19.07
  • Due in Version Undecided
  • Due Date Undecided
  • Private
Attached to Project: OpenWrt/LEDE Project
Opened by Yuxiang Zhu - 04.04.2021

FS#3722 - Software flow offloading breaks ECMP routing

Supply the following if possible:
- Device problem occurs on

 x86_64 Router

- Software versions of OpenWrt/LEDE release, packages, etc.

 OpenWrt 19.07.7 r11306-c4a6851c72, Linux 4.14.221 #0 SMP Mon Feb 15 15:22:37 2021 x86_64 GNU/Linux

- Steps to reproduce

Hey guys,

I met this issue when I was using ECMP (Equal Cost Multi-Path) routing with software flow offload enabled.

Suppose we have topology:

LAN 1 ( ←—> (eth1: OpenWRT (eth2: ←—> ( Other routers ←—> ( LAN 2

1. Add ECMP routes:

$ ip route add nexthop via dev eth2 \
                                nexthop via dev eth2 \
                                nexthop via dev eth2

$ ip route 
	nexthop via dev eth2 weight 1 
	nexthop via dev eth2 weight 1 
	nexthop via dev eth2 weight 1 

2. Setting multipatch hash policy:

sysctl net.ipv4.fib_multipath_hash_policy=1

3. Initiate TCP connections from LAN 1 ( to LAN 2 ( should succeed. Connections are balanced over 3 next hop routers (
4. Enable software flow offloading on LuCI.
5. Open a TCP connection from LAN 1 ( to LAN 2 ( will likely be broken because each packet for a single TCP connection could use a different next hop router to get to the destination.

I’m not sure if this is an OpenWRT issue or upstream kernel issue. Any help would be greatly appreciated.


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