[ovs-discuss] packet segmentation in ovs

[Theodore Elhourani]

This is version 1.10.

Setting the MTUs to take into account the additional GRE headers, was
actually the only way to get packets of   1480<size<1500 to show up on the
tunnel.





On Fri, Aug 23, 2013 at 4:55 PM, Jesse Gross <jesse at nicira.com> wrote:

> On Thu, Aug 22, 2013 at 5:24 PM, Theodore Elhourani
> <telhoura at email.arizona.edu> wrote:
> > If the original packets are of length <= 1400, then they are successfully
> > transmitted through the tunnel. Only when a packet is greater than ~1480
> it
> > gets dropped. You are right the ip stack is fragmenting the large
> packets,
> > but because some of them are a notch below 1500 they are passed as is.
> For
> > these packets, adding gre/ip headers would increase their size to >
> > 1500bytes. Subsequently they are dropped. The reason may be because the
> > packets are already beyond the ip stack of the host, and no further
> > manipulation of the packets is done after this point.
>
> What version is this? If it is before 1.9 then setting
> header_cache=false in the tunnel options may help.
>
> > Reducing the size of packets, via MTU tweaking, seems to be a common
> > practice when gre is used. Any ideas on this ?
>
> Regardless of the outcome of the above, setting the MTUs to take into
> account the additional GRE headers will improve performance.
>
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