[Day 8] 1. Link State (Dynamic Routing)

| | Distance Vector | Link State | | --- | ------------------------------------------------------------------------------------------------------------------ | ----------------------------------------------------------------------------------------------- | | 1 | works with FLSM (Fixed Length Subnet Mask), does not send subnet mask information. | works with VLSM (Variable Length Subnet Mask), it sends the subnet mask information. | | 2 | Sends entire routing table. As the network grows, the table keeps on increasing which might cause bandwidth issue. | Has three types of packets, hello packet, LSA and DD. | | 3 | Works with routing table. | Works with routing table, link-state table and neighbor table. | | 4 | Works with All 1's broadcast (destination IP: 255.255.255.255). | Uses multicast (e.g., 224.0.0.5 for OSPF routers and 224.0.0.6 for OSPF designated routers). | | 5 | Metric : Hops | Metric: Cost = (10^8/Bandwidth) | | 6 | Limit of Hops is 15. | Limit of Hops is 255 hops per area and total are 255 * 65535. (In short, no limit) | | 7 | Only for smaller networks. | Works for medium to large networks. | | 8 | Consumes bandwidth (due to frequent, large updates). | Consumes memory and processing power (due to complex algorithms and network topology database). | | 9 | Simple to implement. | Complex to implement (requires planning and hierarchical addressing) | | 10 | uses Bellman-Ford Algorithm. | uses Dijkstra's Shortest Path First (SPF). | | 11 | Ex - RIP | Ex- OSPF | Metric is nothing but distance. The path with lesser cost is chosen. We still use RIP since it is simple to implement.

Three Types of Link-State Packets

1. Hello Packet:

   • Purpose: Used to establish and maintain neighbor relationships between routers.
   • Sent at regular intervals: Every 10 seconds for links with speeds greater than 1.544 Mbps, or every 30 seconds for links with speeds less than 1.544 Mbps.

2. LSA (Link-State Advertisement):

   • Purpose: Sends updates about changes in the network, particularly concerning unreachable or faulty networks.
   • Key Point: It only carries information about network changes, not the entire routing table, making it more efficient.

3. DD (Database Description):

   • Purpose: Provides a summary of the router's routing table.
   • Sent every 30 minutes to synchronize routing information between routers, ensuring they have consistent data.

Routing Rumors

Routing rumors refer to incorrect or outdated routing information that spreads through a network due to dynamic changes, delays in updates, or temporary inconsistencies in routing protocols.

Example:

In distance-vector routing, such as RIP (Routing Information Protocol), routers exchange routing tables with neighbors. If one router has outdated information, it might propagate this incorrect route as a valid path.

Scenario:

• Router A learns from Router B that a certain network is reachable through Router C.
• However, Router C may have lost its connection to the network but hasn't yet notified Router B.
• Router A continues to propagate this incorrect route, creating a "routing rumor."

These rumors can cause temporary routing loops or inefficient paths until the network stabilizes and the routing protocol updates are synchronized.

• Routing Table:

  • Definition: A table in a router that stores the best routes (paths) to various network destinations.
  • Contents: Destination networks, next-hop addresses, and metrics (e.g., distance or cost).
  • Purpose: Used to determine the best path for forwarding packets.

• Link State Table:

  • Definition: A table that contains detailed information about all the routers and their connected links within the network.
  • Contents: Link states, network topology data, and cost metrics.
  • Purpose: Used by link-state protocols (e.g., OSPF) to calculate the shortest path using algorithms like Dijkstra's.

• Neighbor Table:

  • Definition: A table that lists all the neighboring routers directly connected to a router.
  • Contents: Neighbor router IDs, interface information, and status.
  • Purpose: Maintains information about directly connected routers for establishing routing updates and adjacencies.