3.5.b Implement and troubleshoot neighbor relationship

3.5.b [ii] OTP point-to-point peering

EIGRP Over-the-Top (OTP) is focused on simplifying the deployment of branch networks utilizing an end- to-end EIGRP solution over public and private networks. This simplicity is further enhanced with EIGRP use of OTP to support multiple service provider IP networks.

EIGRP Over the ToP allows the customer to establish EIGRP adjacencies across the MPLS/ VPN provider cloud. An EIGRP targeted adjacency between CPEs is created. This EIGRP neighborship is done via unicast packets , using the CPE ‘WAN’ IP address. This “over the top” peering allows EIGRP to exchange customer prefixes directly between CPEs. Customer prefixes are NOT injected in the providers VRF routing table. In order to allow for proper forwarding of user traffic across the

MPLS/ VPN cloud, user packets are encapsulated on the CPE. The encapsulation header uses the WAN IP address of the CEs, which are known in the MPLS/ VPN cloud.

OTP control plane consists in an EIGRP targeted adjacency between CPEs. Neighborship is established using the CPE WAN address , i.e. address of CPE on the PE/ CPE link, so there is no need for any dynamic routing protocol between the PE/ CPE. The PE just needs to redistribute the connected routes.

This adjacency is using unicast packets and the CPE needs to know the IP of the remote CPE. In the first phase of OTP, only static neighbors are allowed. With manual neighbor configuration, it wouldn’t scale to establish full mesh peering between all CEs. Instead, the concept of Route Reflector, i.e. CPEs peer with RRs only is used and RRs reflect the routes they receive to other CPEs. Each CPE is configured with the RRs WAN address and each RR is configured in EIGRP promiscuous mode, i.e. to accept incoming ‘connections’ (similar to BGP listen feature).

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 3069-3077).  . Kindle Edition.