FlexVPN Spoke to Spoke

This topic is to discuss the following lesson:

Hello,
very nice lesson and well explained. I would just need a clarification here.

In all FlexVPN examples, the tunnel mode you are using is the default one. This means GRE. I tried the labs with a small change under the tunnel interfaces and virtual-templates:

tunnel mode ipsec ipv4

This leads to a direct IPSec encapsulation avoiding the GRE overhead. However, the spoke to spoke direct connectivity is not working. The NHRP redirection fails completely. Hub and spoke communication and spoke to spoke via the hub is fine though.

I am wondering if this is related to my specific software image or it is a normal behavior. Maybe NHRP is only working with GRE encapsulation like we do with classic DMVPN? Any thoughts on this would be much appreciated?

Thanks

Hello Ilias

Unfortunately, NHRP only works with GRE tunnels and doesn’t function with IPsec. Take a look at this Cisco Community thread which details this fact.

The reason is that NHRP can be thought of as a Layer 2 protocol. When encapsulated within a GRE tunnel, it is tunneled as is. With native IPSec tunneling, it attempts to send a Layer 2 protocol over an infrastructure designed for Layer 3, so it fails.

I hope this has been helpful!

Laz

Many thanks Laz. Indeed very helpful!

1 Like

None of the above commands solves it immediately. If you find a way that deletes the virtual-access interface(s) right away (except for a reboot), let me know.

Hello, admin shutting the remote (static) VTIs brings down the virtual-access interface straight away allowing you to make changes and “unshutting” the static VTIs when you are done applying changes to the DVTI

Hello Jason

Great, thanks for sharing your findings with us! I will let Rene know.

Thanks again!

Laz