Distance Vector (RIP) And Link State (OSPF)

A distance vector routing protocol only knows the routing information from where?

From its neighbors, not the entire topology

Process of Distance-Vector Routers when it boots up

1. Creates its own least-cost tree

2. Shares info it knows to its neighbors

How many routes are transferred in one exchange?

Their entire routing table is transferred

Difference between RIP and RIPv2

RIP - Classful

RIPv2 - Classless

What routing protocol is RIP?

Distance Vector

When does RIP consider advertised routes unreachable?

Hop Counts >15

How often does RIP and RIPv2 update?

RIP - Broadcast every 30 seconds

RIPv2 - Multicast every 30 seconds

Message Format of the RIPv1 message

Data Link Frame Header | IP Packer Header | UDP Segment Header | RIP Message

Solution to beat the RIPv1 limitations of Dis-contiguous Networks

Use RIPv2 to include the subnet mask (version 2)

Turn off auto summarization (no auto-summary)

3 major limitations of Classful routing protocols

• Doesn’t support discontinuous networks

• Doesn’t support VLSM

• Doesn’t support CIDR

Command used to examine the contents of the routing updates sent and received by a router

debug ip rip

Common RIPv2 Issues

Incorrectly configured or missing network statements configured with the network command.

What 2 things does the network command do?

-It enables the routing protocol to send and receive updates on any local interfaces that belong to that network.

-It includes the configured network in its routing updates to its neighboring routers.

What is the result of an incorrectly configured or missing network statements configured with the network command?

A missing or incorrect network statement will result in missed routing updates and routing updates not being sent or received on an interface.

Link-State Routing Process

1. Each router learns about its own directly connected networks.

2. Each router is responsible for contacting its neighbors on directly connected networks. (Hello Packets)

3. Each router builds a link-state packet (LSP) containing the state of each directly connected link.

4. Each router floods the LSP to all neighbors, who then store all LSPs received in a database.

5. Each router uses the LSPs to construct a database that is a complete map of the topology and computes the best path to each destination network.

When is an LSP sent?

• During initial setup or router or routing protocol

• Whenever there is a change in the topology

• Neighbor adjacency being established or broke

Cons of Link-State Routing

• More Memory required

• More CPU time

• Temporarily limit bandwidth from flooding LSPs

OSPF Message Encapsulation

Data Link Frame Header | IP Packet Header | OSPF Packet Header | OSPF Packet Type-Specific Data