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 ProtocolRouting 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 invalidatednew advertisements sent to neighbors

(Triggered updates)neighbors in turn send out new

advertisements (if tables changed) link failure info quickly propagates to

entire netpoison 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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