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Re: [Qemu-devel] Qemu-KVM VETH

From: Tim Epkes
Subject: Re: [Qemu-devel] Qemu-KVM VETH
Date: Tue, 24 Sep 2013 15:55:04 -0400


I just tested the most recent version of qemu (1.4).  I have 2 virtual images back to back via a tcp socket.  They can ping eachother, but when I down the listener and bring it back up (meaning killing the kvm and relaunching) it cannot ping anymore.  The connector never retries to connect.  This is the most viable solution for the LLDP and ISIS issues.  Thanks


On Fri, Sep 20, 2013 at 1:26 PM, Stefan Hajnoczi <address@hidden> wrote:
On Fri, Sep 20, 2013 at 11:48:50AM -0400, Tim Epkes wrote:
> The problem aI face is that a bridge in the middle ( using taps) breaks
> LLDP ( L2 discovery protocol) and should break ISIS as well.  Sockets
> aren't bad, but if for some reason I take the listener VM down and bring
> back up, then I have to bring down all connector VMs, which chains on
> itself if there is a lot of connectivity defined.  When UDP was available
> that wasn't an issue.

I just checked linux.git but this patch has not been applied (although
it's trivial if you're willing to rebuild your kernel from source):

It sounds like improving net/socket.c might be the right place to look.

> Anyway, that is how I came to VETHs.  I am aware that you can use UDP
> multicast, but performance past one hop is extremely poor ( resulting in 3
> of 5 pings to be lost.  Thanks

Unfortunately the veth driver does not hand Ethernet frames to/from
userspace.  We really need something tap-like where userspace can
inject/extract packets.


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