This post will build off my last one, DMVPN, and here we will discuss the routing protocol options as well as each of their configurations. This is more of a Why? What? Eh? type of post – hence the picture. Here I will show how to use CDP for a routing protocol – yes, CDP.
Right from the Cisco kool-aid website: On-Demand Routing (ODR) is an enhancement to Cisco Discovery Protocol (CDP), a protocol used to discover other Cisco devices on either broadcast or non-broadcast media. With the help of CDP, it is possible to find the device type, the IP address, the Cisco IOS® version running on the neighbor Cisco device, the capabilities of the neighbor device, and so on. In Cisco IOS software release 11.2, ODR was added to CDP to advertise the connected IP prefix of a stub router via CDP. This feature takes an extra five bytes for each network or subnet, four bytes for the IP address, and one byte to advertise the subnet mask along with the IP. ODR is able to carry Variable Length Subnet Mask (VLSM) information.
In order to get this lab to work I had to tweak a few configs on the routers, namely I had to remove the 0/0 route I had pointing to the ISP and make it a more specific – 126.96.36.199/8 pointing to the “ISP” router as the next hop. With ODR only a default route (0/0) is passed from the hub to the spokes, so no other default route can exist.
Quick note: When I am posting the configurations for the sites I will only notate the routing protocol additions. If you need information on DMVPN configuration, see my previous post.