On Thu, Sep 01, 2016 at 05:17:44PM +0000, Daniele Di Proietto wrote:
> Let me try to sum up the problem further
>
> 1) Behavior on master, before commit 47bf118665a3("ofproto: Always set MTU
> for new internal ports."):
>
> a) When an internal interface is added, or its MTU has changed we only
> change its MTU if it is bigger than the bridge minimum
> b) When a non internal, non tunnel port is added, we reconfigure every
> internal interface to match exactly the bridge minimum, no matter what
> c) If the bridge doesn't have physical ports (only tunnels and
> internals), we consider the minimum mtu to be invalid and we don't change the
> internal interfaces mtu
>
> I felt that there was an inconsistency between 1a and 1b. I thought 1c was
> not very clean, because the current configuration depends on the previous
> state (if there were physical ports at some point, we would lower the
> internal interfaces mtu, but we couldn't restore it when they were removed)
>
> 2) Behavior on master after commit 47bf118665a3("ofproto: Always set MTU for
> new internal ports."):
>
> a) When an internal interface is added, or its MTU has changed we
> overwrite its MTU with the bridge minimum.
> b) When a non internal, non tunnel port is added, we reconfigure every
> internal interface to match exactly the bridge minimum, no matter what
> c) If the bridge doesn't have physical ports (only tunnels and
> internals), we consider the minimum mtu to be 1500. We therefore force every
> internal interface to be 1500.
>
> Behavior b is the same. Behavior a is changed to match more closely behavior
> b. Behavior c is changed completely. Now the current configuration doesn't
> depend on the previous state.
> When I made the change I didn't think that there were valid use cases for
> allowing the user to configure internal interfaces MTU. The test suite
> obviously proved me wrong.
>
> ---------
>
> Proposed solution:
>
> A) This patch.
>
> Since OVS is not able the control the MTU in case of tunnelling or MPLS,
> stop doing it entirely. The systems that relied on the old behavior need to
> be updated.
>
> B) We could consider an hybrid solution that keeps backwards compatibility
> for tunnelling use cases (like our testsuite).
>
> 2a)
> 2b or 1b)
> 1c)
>
>
>
>
> This would not solve the problem for MPLS. MPLS uses physical devices, so
> the internal interface would be forced to match the physical interfaces and
> this is not OK for MPLS (or double vlans). Also, this solution keeps
> behavior 1c, which makes the mtu assignment "stateful".
>
> Other ideas?
>
> Thanks,
>
> Daniele
How about we let the interfaces to have a less than minimum MTU? Would that
solve the problem with tunnels/overlays?
Then, we partially revert the patch, like below. This has fixed at least the
VXLAN system test for me.
Cascardo.
diff --git a/ofproto/ofproto.c b/ofproto/ofproto.c
index 9d62b72..6383dc8 100644
--- a/ofproto/ofproto.c
+++ b/ofproto/ofproto.c
@@ -2752,8 +2752,10 @@ update_mtu(struct ofproto *p, struct ofport *port)
return;
}
if (ofport_is_internal(p, port)) {
- if (!netdev_set_mtu(port->netdev, p->min_mtu)) {
- dev_mtu = p->min_mtu;
+ if (dev_mtu > p->min_mtu) {
+ if (!netdev_set_mtu(port->netdev, p->min_mtu)) {
+ dev_mtu = p->min_mtu;
+ }
}
port->mtu = dev_mtu;
return;
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