I have a DMVPN setup using simple GRE and VRF's with one Hub and a few spokes. At one client we are having MTU issues where we have had to manually change the MTU of the servers on the hub side and the clients on the spoke side to 1476 or lower. I realize this is due to GRE overhead but I dont understand where the negotiation is failing and how to resolve it without manually changing MTU on all of the devices (some devices have no option to set MTU).
I have read about writing a policy map to clear the DF bit and adjust the MTU size...is this the proper method? I have also read about the tunnel path-mtu-discovery command but I dont have a test router handy and I am unsure if this command is on the tunnel by default. Anyone have any experiance with GRE tunnels and possible MTU issues that could shed some light on this for me? Below are some of my config if it helps.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...