[FS#3722] Software flow offloading breaks ECMP routing
openwrt-bugs at lists.openwrt.org
Sun Apr 4 17:07:57 BST 2021
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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
- 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
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 (192.168.1.0/24) (eth1: 192.168.1.1/24) OpenWRT (eth2: 192.168.2.1/24) (192.168.2.51-53/24) Other routers (192.168.150.0/24) LAN 2
1. Add ECMP routes:
$ ip route add 192.168.150.0/24 nexthop via 192.168.2.51 dev eth2 \
nexthop via 192.168.2.52 dev eth2 \
nexthop via 192.168.2.53 dev eth2
$ ip route
nexthop via 192.168.2.51 dev eth2 weight 1
nexthop via 192.168.2.52 dev eth2 weight 1
nexthop via 192.168.2.53 dev eth2 weight 1
2. Setting multipatch hash policy:
3. Initiate TCP connections from LAN 1 (192.168.1.0/24) to LAN 2 (192.168.150.0/24) should succeed. Connections are balanced over 3 next hop routers (192.168.2.51-53).
4. Enable software flow offloading on LuCI.
5. Open a TCP connection from LAN 1 (192.168.1.0/24) to LAN 2 (192.168.150.0/24) 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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