RD-CSY3021 Comparing Routing Protocols

RD-CSY3021 Criteria used to compare routing protocols includes  Time to convergence  Proprietary/open standards  Scalability  Classful/Classless  Metric used  Resource usage  Implementation & maintenance

RD-CSY3021 Two Main Approaches  Distance Vector Protocols ◦ E.g., RIP V1 and v2 (Routing Information Protocol) ◦ EIGRP  Link State Protocols ◦ E.g., OSPF (Open Shortest Path First)  Our Focus ◦ Comparing them

 Classful vs. Classless Routing Behavior -It is recommended to use classless routing behavior  Reason: so supernet and default routes can be used whenever needed

 Classless Routing Protocol Routing updates include the subnet mask  Supports VLSM  Supports Route Summarization

RD-CSY3021 Algorithm - procedure for accomplishing a certain task

 Link State (LS) advantages:  More stable (aka fewer routing loops)  Faster convergence than distance vector  Easier to discover network topology, troubleshoot network.

 Uses hop count as metric (max: 16 is infinity)  Tables (vectors) “advertised” to neighbors every 30 s.  Each advertisement: upto 25 entries  No advertisement for 180 sec: neighbor/link declared dead  routes via neighbor invalidated  new advertisements sent to neighbors (Triggered updates)  neighbors in turn send out new advertisements (if tables changed)  link failure info quickly propagates to entire net  poison reverse used to prevent ping- pong loops (infinite distance = 16 hops)

 Split horizon/poison reverse does not guarantee to solve count-to-infinity problem ◦ 16 = infinity => RIP for small networks only! ◦ Slow convergence  Broadcasts consume non-router resources  RIPv1 does not support subnet masks (VLSMs) ◦ No authentication

RD-CSY3021

 Why ? Installed base of RIP routers  Provides: ◦ VLSM support ◦ Authentication ◦ Multicasting  Uses reserved fields in RIPv1 header.  Supports authentication.

 Key: Create a network “map” at each node.  1. Node collects the state of its connected links and forms a “Link State Packet” (LSP)  2. Flood LSP => reaches every other node in the network and everyone now has a network map.  3. Given map, run Dijkstra’s shortest path algorithm (SPF) => get paths to all destinations  4. Routing table = next-hops of these paths.  5. Hierarchical routing: organization of areas, and filtered control plane information flooded.

 Reliable Flooding: sequence #s, age  Neighbor discovery and maintenance (hello)  Efficiency in Broadcast LANs ◦ designated router (DR) concept  Areas and Hierarchy ◦ Area types: Normal, Stub, NSSA: filtering ◦ External Routes (from other ASs), interaction with inter-domain routing.

 Information hiding (filtered) => ◦ less computation, =>  less bandwidth requirement =>  Less storage =>  Improved efficiency => leads to scalable networks

 Two-level hierarchy: local area, backbone.  Link-state advertisements only in area  each nodes has detailed area topology; only know direction (shortest path) to nets in other areas.  Two-level restriction avoids count-to-infinity issues in backbone routing.  Area border routers (ABR): “summarize” distances to networks in own area, advertise to other Area Border routers.  Backbone routers: uses a DV-style routing between backbone routers  Boundary routers connect to other ASs (generate “external” records)

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