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Date: Fri, 3 Jun 2011 12:36:32 -0700 From: Andrew Morton <akpm@...ux-foundation.org> To: netdev@...r.kernel.org Cc: bugzilla-daemon@...zilla.kernel.org, bugme-daemon@...zilla.kernel.org, igor@...g.net, Stephen Hemminger <shemminger@...ux-foundation.org> Subject: Re: [Bugme-new] [Bug 36602] New: Bridge fails to work normally without net.ipv4.ip_forward=1 (switched to email. Please respond via emailed reply-to-all, not via the bugzilla web interface). On Fri, 3 Jun 2011 19:21:20 GMT bugzilla-daemon@...zilla.kernel.org wrote: > https://bugzilla.kernel.org/show_bug.cgi?id=36602 > > Summary: Bridge fails to work normally without > net.ipv4.ip_forward=1 > Product: Networking > Version: 2.5 > Kernel Version: 2.6.38.7 > Platform: All > OS/Version: Linux > Tree: Mainline > Status: NEW > Severity: normal > Priority: P1 > Component: Other > AssignedTo: acme@...stprotocols.net > ReportedBy: igor@...g.net > Regression: No > > > Yes, this seems strange, but it's seems to be true. > > My network scheme is quite simple: > > (host1) <--- 10gbe ---> (bridge host) <--- 10gbe ---> (host2) > > host1 & host2 are actually VMWare ESXi hypervisors, but that's irrelevant in > this case i think. > > Network adapters are Intel's 82599 10 gig cards on all hosts. > > At the bridge, on each interface i've created a vlan, and then bridged them: > # vconfig add eth0 102 > # vconfig add eth1 102 > # brctl addbr br0 > # brctl addif br0 eth0.102 > # brctl addif br0 eth1.102 > # ip link set br0 mtu 9000 up > ...etc... > > At this point, the bridge seems to be working, i can ping between host1 & > host2, even with jumbo frames without fragmentation. > > BUT when i am trying to use iperf & friends to measure raw tcp speed between > hosts 1/2, i'm getting something weird like 7-10 MEGABITS per second, or even > an iperf hang until ctrl+c. > > If i attach an ip address to the bridge, and measure between hosts and the > bridge, it works flawlessly, rendering 9.8Gbit/s in both directions. > > While trying to find a solution, when i ran out of options, i've set > net.ipv4.ip_forward to 1, and, SURPRISE, the bridge started to work like a > charm, at almost 10gig speed. > > What makes it stranger, is that in my kernel, i've turned off all routing code, > iptables and other stuff, as this host serves primarily as iSCSI target. > > I have little knowledge in kernel's deep internals, but i always thought that > bridging & routing are on different levels of operation and couldn't affect > each other (ebtables is an exception, but i don't have it :) ). > > Maybe i'm interpreting the results wrong, but i've ruled out everything else. > > Currently, i can't use this setup as a test ground, i'll try to replicate the > scheme in a virtual environment to see if other kernels are affected as well. > > Glad to hear any ideas on this. > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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