OpenWrt/LEDE Project

  • Status Unconfirmed
  • Percent Complete
    0%
  • Task Type Bug Report
  • Category Base system
  • Assigned To No-one
  • Operating System All
  • Severity High
  • Priority Very Low
  • Reported Version openwrt-19.07
  • Due in Version Undecided
  • Due Date Undecided
  • Private
Attached to Project: OpenWrt/LEDE Project
Opened by supersebbo - 27.06.2020

FS#3207 - Setting MTU on Bridged interfaces does not set MTU on member interfaces

- Device problem occurs on - x86
- Software versions of OpenWrt/LEDE release, packages, etc. - 19.07.3

 

I think it’s a bug/overlooked use case, but when you have interfaces bridged in the UCI config, the MTU setting does not get applied to the member interfaces (physical or VLAN).

config interface 'lan'
        option proto 'static'
        option netmask '255.255.255.0'
        option ip6assign '60'
        option ipaddr '192.168.1.1'
        option type 'bridge'
        option mtu '9000'
        option ifname 'eth1 eth4.10'

When I boot using this config I have connectivity issues with devices using Jumbo frames. ifconfig confirms that MTUs on the members interfaces are still at default 1500.

eth1      Link encap:Ethernet  HWaddr 0C:C4:7A:AB:39:3D
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
          Memory:df440000-df45ffff

eth4      Link encap:Ethernet  HWaddr 3C:FD:FE:BB:01:50
          inet6 addr: fe80::3efd:feff:febb:150/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500 Metric:1
          RX packets:50176 errors:0 dropped:1 overruns:0 frame:0
          TX packets:37468 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:15692679 (14.9 MiB)  TX bytes:29263711 (27.9 MiB)

eth4.10   Link encap:Ethernet  HWaddr 3C:FD:FE:BB:01:50
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:36728 errors:0 dropped:0 overruns:0 frame:0
          TX packets:20850 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:9314410 (8.8 MiB)  TX bytes:26473088 (25.2 MiB)

I have to manually use the ifconfig tool to set the MTU (i.e. ifconfig eth4.10 mtu 9000) to get the network back up and running correctly.

Obviously these commands could be scritped, however it was my understanding the UCI network config should be doing this .

Mike Klemencic commented on 22.10.2021 11:35
~ ip link |grep -C 3 br-lan
  link/ether d8:58:d7:01:03:c4 brd ff:ff:ff:ff:ff:ff
4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9000 qdisc mq state UP qlen 532
  link/ether 00:e0:a6:de:ca:de brd ff:ff:ff:ff:ff:ff

5: lan0@eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master br-lan state UP qlen 1000

  link/ether d8:58:d7:01:03:c4 brd ff:ff:ff:ff:ff:ff

6: lan1@eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master br-lan state UP qlen 1000

  link/ether d8:58:d7:01:03:c4 brd ff:ff:ff:ff:ff:ff

7: lan2@eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master br-lan state UP qlen 1000

  link/ether d8:58:d7:01:03:c4 brd ff:ff:ff:ff:ff:ff

8: lan3@eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master br-lan state UP qlen 1000

  link/ether d8:58:d7:01:03:c4 brd ff:ff:ff:ff:ff:ff

9: lan4@eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9000 qdisc noqueue state UP qlen 1000

  link/ether 00:e0:a6:de:c1:de brd ff:ff:ff:ff:ff:ff

  link/ether 92:39:95:ed:a6:78 brd ff:ff:ff:ff:ff:ff

20: br-iwan: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN qlen 1000

  link/ether 2e:a9:e3:96:13:64 brd ff:ff:ff:ff:ff:ff

21: br-lan: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP qlen 1000

  link/ether 04:f0:21:42:16:24 brd ff:ff:ff:ff:ff:ff

27: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master br-lan state UP qlen 1000

  link/ether 04:f0:21:42:16:24 brd ff:ff:ff:ff:ff:ff

34: ifb4br-guest_tu: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc htb state UNKNOWN qlen 32

  link/ether 42:97:94:b6:e2:6f brd ff:ff:ff:ff:ff:ff

37: vethG7BXN4@if36: <BROADCAST,MULTICAST,UP,LOWER_UP,M-DOWN> mtu 1500 qdisc noqueue master br-lan state UP qlen 1000

  link/ether fe:83:ba:ac:4d:5b brd ff:ff:ff:ff:ff:ff

39: vethPS8UH3@if38: <BROADCAST,MULTICAST,UP,LOWER_UP,M-DOWN> mtu 1500 qdisc noqueue master br-lan state UP qlen 1000

  link/ether fe:6d:4a:e0:03:33 brd ff:ff:ff:ff:ff:ff

➜ ~ ip link set br-lan mtu 9000
ip: SIOCSIFMTU: Invalid argument
➜ ~ sysctl -w net.ipv6.conf.br-lan.mtu=9000
sysctl: write error: Invalid argument
➜ ~ sysctl net.ipv6.conf.br-lan.mtu
net.ipv6.conf.br-lan.mtu = 1500

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