[FS#3722] Software flow offloading breaks ECMP routing

OpenWrt Bugs openwrt-bugs at lists.openwrt.org
Sun Apr 4 17:07:57 BST 2021


A new Flyspray task has been opened.  Details are below. 

User who did this - Yuxiang Zhu (vfreex) 

Attached to Project - OpenWrt/LEDE Project
Summary - Software flow offloading breaks ECMP routing
Task Type - Bug Report
Category - Kernel
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - Low
Priority - Very Low
Reported Version - openwrt-19.07
Due in Version - Undecided
Due Date - Undecided
Details - 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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