[ovs-discuss] double the encap

[Brandon Heller]

I'd like to configure OVS using OpenFlow+Nicira extensions to push two VLAN
tags, to load-balance at higher levels of a multi-rooted tree on physical
switches that only support OpenFlow 1.0 in firmware and so don't support
ECMP.  Double-stacked VLANs aren't strictly necessary; double IP-in-IP or
VLAN + IP-in-IP would probably work too.

One possibility may be to use a nicira_header to add a VLAN header with
OFPAT_SET_VLAN_VID and then output to NXAST_RESUBMIT.   The resubmit match
would then need to encap a VLAN the next time rather than set it, and I
don't see an action for that other than maybe tunneling.

Questions:
What is the preferred approach to get this behavior, of double-pushing VLAN
or other tags from edge OVS instances?
Is there documentation on the use of Nicira extensions outside
of include/openflow/nicira-ext.h that I should pay attention to?

Thanks,
Brandon
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