IPSec tunnel natively does not support multicast traffic, and dynamic routing protocols by default is running on multicast.
You would need to check whether the routing updates are exchanged via multicast, or it has neighbour statement that changed it to unicast hence it works through IPSec tunnel. If you would like to use the native multicast dynamic routing protocols through ipsec tunnel, you would need to encapsulate those multicast traffic in GRE first prior to it being encrypted with IPSec.
Another possibility apart from it being unicast traffic is possible the routing updates are exchanged NOT through the IPSec tunnel, but through your backdoor (possible MPLS cloud) internally.
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...