Dynamic Routing

1
Dynamic Routing

• Comparing Routing Protocols

2
Criteria to compare routing protocols

• Criteria used to compare routing protocols
  includes
• Time to convergence
• Proprietary/open standards
• Scalability
• Classful/Classless
• Metric used
• Resource usage
• Implementation maintenance

3
Interior Gateway Routing

• 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

4
Routing Behavior

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

5
Characteristics of classless routing protocols

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

6
Routing Protocol Algorithm

• Algorithm - procedure for accomplishing a certain
  task

7
Link State vs. Distance Vector

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

8
RIP Routing Information Protocol

• 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)

9
RIPv1 Problems (Continued)

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

10
Configuring RIP
11
RIPv2

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

12
Link State Protocols

• 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 gt reaches every other node in the
  network and everyone now has a network map.
• 3. Given map, run Dijkstras shortest path
  algorithm (SPF) gt 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.

13
Link State Issues

• 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.

14
Hierarchical Routing

• Information hiding (filtered) gt
• less computation, gt
• less bandwidth requirement gt
• Less storage gt
• Improved efficiency gt leads to scalable
  networks

15
Hierarchical OSPF
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Hierarchical OSPF

• 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)

17
Sample Area Configuration
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