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How to do dynamic routing over a VPN tunnel




This document describes the process of implementing dynamic routing over a VPN tunnel.


WHat is Dynamic Routing?


Dynamic routing can be defined as a process which renders optimal data routing. Dynamic routing empowers routers to select the paths according to real-time layout changes in logical network.Routing protocol running on the router takes care of the creation, maintenance and updating of the dynamic routing table where as in static routing, all jobs are required to be performed by user manually.


Most commonly used dynamic routing protocol are:

  • Routing Information Protocol (RIP)
  • Open Shortest Path First (OSPF)


Dynamic routing can be explained as mentioned below:

  • Router delivers and receives routing messages at router interfaces.
  • Routing information is shared with other routers, which are using the same routing protocol.
  • Routers keep swaping the routing messages in order to discover information about other remote networks.
  • Whenever change in topology takes place a triger is sent to the router and topology change is advertised to other routers.



IPSec supports the encryption of unicast IP traffic only. Therefore, routing protocols like Enhanced Interior Gateway Routing Protocol (EIGRP) and Open Shortest Path First (OSPF) and non-IP traffic like Internetwork Packet Exchange (IPX) and AppleTalk are unable to be encrypted using IPSec.


For a workaround, encapsulate such traffic in Generic Routing Encapsulation (GRE) before encryption, using a GRE over an IPSec configuration.

With GRE over IPSec, traffic will be encapsulated first and then encrypted.

For configuration examples, refer to these documents: