CCNP Enterprise Core (350-401)

OSPF runs directly on IPv4, using it’s own protocol numbered 89, reserved for OSPF by IANA (Internet Assigned Numbers Authority). OSPF uses multicast where possible to reduce unnecessary broadcast or unicast traffic: Multicast address 224.0.0.5 or MAC 01:00:5E:00:00:05. All Routers using OSPF receive these packets. Multicast address 224.0.0.6 or MAC 01:00:5E:00:00:06. Only designated routers receive…

OSPF, or Open Shortest Path First is a link state routing protocol. It is a non proprietary Interior Gateway Protocol. OSPF version 2 is defined in RFC 2328 and supports IPv4. OSPF version 3 is defined in RFC 5340 and supports IPv6 OSPF works by sending neighbouring routers link state advertisements (LSAs) that contain the…

To scale an EIGRP system effectively, it requires summarisation. EIGRP can summarise network prefixes on an interface basis. Prefixes contained within the summarisation are suppressed with the summary route being advertised instead, although the summary route is only advertised if a suppressed prefix is valid within the summary route. Route summarisation also creates a query…

Hello and Hold Timers An EIGRP hello packet is not just for forming new adjacencies, but is used for checking that the neighbour is working and responsive. By default EIGRP hello packet is sent out every 5 seconds, or 60 seconds on a slow speed interface (T1 or lower) EIGRP uses a timer called a…

Equal Cost Load Balancing EIGRP permits multiple successor routes with an equal metric to be installed into the routing table for load balancing. Installing multiple routes for the same prefix is known as equal cost multipathing, or ECMP. Unequal Cost Load Balancing EIGRP also supports unequal-cost load balancing, which permits the installation of the successor…

Before EIGRP IGRP uses multiple factors to calculate the metric for a path. Metric calculation uses bandwidth and delay by default, but can include load and reliability too. Metric = (K1 * Bandwidth + ( (K2 * Bandwidth) / (256 – Load) ) + K3 * Delay) * ( K5 / (K4 + Reliability) IGRP…

When an adjacency is formed, neighbouring EIGRP routers exchange their entire routing table, following exchanges only contain partial updates as the topology changes in the network. EIGRP uses five different types of packets to communicate with other routers, with it’s own IP number – 88. Type Packet Name Function 1 Hello Discovering EIGRP neighbour and…

In EIGRP there is a topology table that is separate from the routing table. This topology table makes EIGRP different from a traditional distance vector protocol and contains information to identify loop-free routes. Each entry in this topology table contains: The network prefix EIGRP neighbors that have advertised that network prefix The metrics from each…

Term Definition Feasible Successor A route that satisfies a feasibility condition and is kept as a backup route. The condition is that the backup route is loop free. Feasibility Condition The condition that for a route to be considered a backup route, the reported distance received must be less than the feasible distance calculated locally.…

A router can run multiple EIGRP processes. Each process operates under a unique number known as a Autonomous System, or AS number. In EIGRP, only routers with the same AS number can exchange routes with each other and form neighbour relationships. If a router operates multiple EIGRP processes, a router will not transmit routes learned…