@kjstech - running into the same case as of today,
I have an Extreme L3 switch that need to establish a GRE tunnel with a Cisco router from the ISP side,
but the additional thing here is an IPSEC VPn between an ASA and the same Cisco router to secure the GRE tunnel, the IP I've put is the only thing I have, any suggestion please for the Extreme switch configuration?
While we got point to point connectivity, we abandoned this a long time ago because at the time (not sure if this is still the case in newer firmwares) - we couldn’t include the GRE tunnel interface in OSPF calculation on the extreme side. We always had to just OSPF to another device that DOES have that capeability, such as a Cisco Router, Server running pfsense with the frr plugin, or Ubiquiti EdgeRouter.
We ended up canceling our LTE backup (too slow and too much latency) and moved to cable modem. Now we OSPF with a higher cost to a pfsense box which establishes IPSEC tunnel over a cable modem to another pfsense box at our HQ.
The local carriers private fiber metro Ethernet is a lower cost route but if it’s cut, OSPF re-converges over to pfsense, out a IPsec tunnel to HQ, then OSPF back into an extreme core.
Overall this back up solution works much faster and the bandwidth with this far greater than a previous LTE solution we were using. Plus it’s cheaper and pfsense is free. We already have a local file and print server at each location so it just spinning up another VM with pfsense on it and using additional Ethernet ports on the 1U server.
Below is a very basic example from EXOS:
It sounds like most of the magic in your situation is happening on the Cisco side of things so not sure what additional configuration you would need from EXOS regarding that topology.