GRE keepalives with VRF

Question

GRE keeplives enabled under tunnel interfaces will put the line protocol of tunnel to down... I have tested this in LAB !!!
why is it so , what is the workaround to use keepalives with VRF ........

Answer 1

Hello,
It is caused by the way how the GRE keepalives work. I suggest reading these two documents first:
http://www.cisco.com/en/US/tech/tk827/tk369/technologies_tech_note09186a008048cffc.shtml
http://www.cisco.com/en/US/tech/tk827/tk369/technologies_tech_note09186a008040a17c.shtml
In short, a router sending keepalive in essence constructs an IP packet whose source is the remote endpoint and recipient is the router itself. It then encapsulates it using GRE and attaches another IP header to it with the send being itself and destination being the remote end. This packet will be sent to the remote end, there it will be decapsulated and afterwards it will be routed as usual, thereby returning the inner IP packet back to the original sender.
Obviously, this keepalive mechanism is not integrated with the VRF feature. The keepalive packet may arrive at the remote endpoint but after it is decapsulated the association with the receiving Tunnel interface is obviously lost and the remote endpoint tries to route that packet back using the global routing table, not the VRF in which the tunnel resides. This in turn causes the keepalive packet to never return.
I am unfortunately not aware of any backup keepalive mechanism for this, apart of running routing protocols over the tunnel with more aggresive hello and dead intervals.
Best regards,
Peter