Explanation/Reference:
Section: Enterprise Network Design Explanation
Explanation:
Redistribution is an advanced routing feature that increases the scalability of a network design by facilitating the coexistence of multiple routing protocols. Redistribution is typically performed by routers between the enterprise campus core and the enterprise edge. For example, to join a campus network running Enhanced Interior Gateway Routing Protocol (EIGRP) with a branch network running Open Shortest Path First (OSPF), Cisco recommends that you configure two-way redistribution with route map filters at each location. Advanced routing features, such as redistribution, route filtering, and summarization, can greatly impact the functionality and scalability of a network and, thus, should be carefully considered during the network design process.
Route filtering is an advanced routing feature that can be used to block route advertisements that could create routing loops. Routing loops occur when a topology change or a delayed routing update results in two routers pointing to each other as the next hop to a destination. For example, Router1 has a path to Router2 that begins with Router3, and Router3 has a path to Router2 that begins with Router1. Since both Router1 and Router3 send data to each other that is intended for Router2, they will continuously bounce the data back and forth between them, thus forming a loop. In order to prevent this loop, a route filter could be used to stop the path from Router1 to Router2 from being advertised to Router3. Consequently, when Router3 receives data from Router1 that is intended for Router2, the only route available is its own path directly to Router2. Because route filtering is often used in conjunction with redistribution, route filtering is typically performed by routers between the enterprise campus core and the enterprise edge.
Route summarization, which is also known as supernetting, is an advanced routing feature that enables a router to advertise multiple contiguous subnets as a single, larger subnet. Summarization combines several smaller subnets into one larger subnet. This enables routers on the network to maintain a single summarized route in their routing tables. Therefore, fewer routes are advertised by the routers, which reduces the amount of bandwidth required for routing update traffic. Route summarization is most efficient when the subnets can be summarized within a single subnet boundary and are contiguous, meaning that all of the subnets are consecutive. Summarization is typically performed between the enterprise campus core and the enterprise edge.
Redundancy is the repetition built into a network design to protect the network from unnecessary vulnerabilities or downtime that might be caused by having a single point of failure. Simply put, redundancy is having a backup plan in place that can be used in the event that the primary plan becomes unavailable.
For example, multiple physical links between two switches could be used to promote redundancy.
Reference:
CCDA 200-310 Official Cert Guide, Chapter 2, Route Redundancy, pp. 63-64 CCDA 200-310 Official Cert Guide, Chapter 11, Route Summarization, pp. 455-458 CCDA 200-310 Official Cert Guide, Chapter 11, Route Redistribution, pp. 458-461 CCDA 200-310 Official Cert Guide, Chapter 11, Route Filtering, pp. 461-462 Cisco: Redistributing Routing Protocols: Introduction
Cisco: OSPF Design Guide: OSPF and Route Summarization
Cisco: Filtering Routing Updates on Distance Vector IP Routing Protocols: Introduction Cisco: Cisco Unified Communications System IP Telephony for Enterprise and Midmarket 7.0(1):
Redundancy