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Opened 8 years ago

Last modified 2 years ago

#7537 accepted defect

Bridge doesn't conform to MTU setting

Reported by: Sami Olmari <jaarli@…> Owned by: jow
Priority: normal Milestone:
Component: base system Version: Backfire 10.03
Keywords: mtu, bridge, jumboframe Cc:

Description

in x86 openwrt when I set LAN MTU to 9000, it doesn't work when LAN is bridged. MTU stays at 1500 even after reboot.

If I make LAN a single device (no bridging), then MTU of 9000 works as expected, after reboot(!)

As soon as there is bridge even with single device mtu stays at 1500, no matter if the single device is same where mtu 9000 works nonbridged.

Also mtu stays at 1500 in Buffalo whr-hp-g54 brcm47xx version when set to 9000, bridged or not, but I'm not 100% sure does that device support jumbo frames (but I think it does even when 100mbps only).

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Change History (6)

comment:1 Changed 8 years ago by Sami Olmari <sami@…>

I can confirm x86 mtu issue still beign present in trunk snapshot r22048, download dated 04-Jul-2010

comment:2 Changed 7 years ago by Wicher Minnaard <wicher@…>

From http://www.linuxfoundation.org/collaborate/workgroups/networking/bridge :
"All devices share the same maximum packet size (MTU). The bridge doesn't fragment packets."
May have something to do with this. Maybe you need to give each interface the right (and same) MTU before assembling the bridge.

comment:3 Changed 7 years ago by Sami Olmari <sami.palvelut@…>

Well that should be handled by OpenWRT anyways... Also it happends when eth0 is only member in the bridge, and MTU still stays at 1500 at bridge, even when eth0 had MTU of 9000 before attaching to bridge, this test was byproduct of trying to determine where the MTU problem is at the first place :)

comment:4 Changed 7 years ago by jow

  • Owner changed from developers to jow
  • Status changed from new to accepted

comment:5 Changed 2 years ago by xuefer@…

openwrt should set mtu for all device it try to bridge. this bug is not fixed as of now

comment:6 Changed 2 years ago by anonymous

openwrt should set mtu for all device it try to bridge. this bug is not fixed as of now

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