CST3607 Class Notes 2019-03-21

News and Tools

LammleSim has been replaced by the Cisco Packet Tracer

Cisco Discovery Protocol (CDP)

  • Chapter 7: Page 289

How Routers Talk to Each Other

Router Configuration Checklist

  • Identify the interfaces on the router that are going to be used.
  • Identify the directly connected networks.
  • Configure the IP address and subnet mask on only those interfaces on the router that are going to be used.
  • Enable the interface(s) : no shutdown
  • Add the routing protocol
    • Add only the network address for each “directly connected” network

Delivery of a Packet

  • Direct Delivery
    • Direct delivery occurs when the source and destination of the packet are located on the same physical network or when the delivery is between the last router and the destination host.
  • Indirect Delivery
    • If the destination host is not on the same network as the deliverer, the packet is delivered indirectly.In an indirect delivery, the packet goes from router to router until it reaches the one connected to the same physical network as its final destination.A delivery always involves one direct delivery but zero or more indirect deliveries.The last delivery is always a direct delivery.

Routing protocols


  • A unit of measure used by routing protocol algorithms to determine the best pathway for traffic to use to reach a particular destination.
  • Routers use various metrics and calculations to determine the best route for a packet to reach its final network destination.
  • Each routing protocol uses its own algorithm with varying weights to determine the best possible path.

An interior gateway protocol (IGP) is a routing protocol that is used within an autonomous system (AS).

Interior gateway protocols can be divided into two categories

  • Distance-vector routing protocols
    • e.g. RIP, IGRP, EIGRP
    • A distance-vector routing protocol requires that a router inform its neighbors of topology changes periodically and, in some cases, when a change is detected in the topology of a network.
  • Link-state routing protocols
    • e.g. OSPF, Intermediate System to Intermediate System (IS-IS)
    • link-state protocols require a router to inform all the nodes in a network of topology changes

An Exterior Gateway Protocol (EGP) is used between autonomous systems.

Forwarding Techniques

Techniques to make the size of the routing table manageable.

  • Next-Hop Method vs. Route Method
    • The routing table holds only the address of the next hop instead of information about the complete route (route method).
  • Network-Specific Method vs. Host-Specific Method
    • Instead of having an entry for every destination host connected to the same physical network (host-specific method), we have only one entry that defines the address of the destination network (Network-Specific Method).
  • Default Method
    • Default routing is used to send packets with a remote destination network not in the routing table to the next hop router.

Routing Protocol Vectors/Categories

ProtocolCategory / VectorDescription
RIP (Routing Information Protocol)distance-vector routingClassified as an interior gateway protocol (IGP)
Maximum hop count of only 15, and a single routing metric
IGRP (Interior Gateway Routing Protocol)distance-vector routingConsidered a classful routing protocol
IGRP supports multiple metrics for each route, including bandwidth, delay, load, MTU, and reliability
Maximum hop count of IGRP-routed packets is 255 (default is 100)
EIGRP (Enhanced Interior Gateway Routing Protocol)distance-vector routingAdds support for VLSM (variable length subnet mask)
Adds the Diffusing Update Algorithm (DUAL) in order to improve routing and provide a loopless environment.
EIGRP has completely replaced IGRP
OSPF (Open Shortest Path First)link-state routing protocolRoutes packets based solely on the destination IP address found in IP packets.
Designed to support variable-length subnet masking (VLSM, CIDR).
OSPF detects changes in the topology, such as link failures, very quickly and converges on a new loop-free routing structure within seconds.
Falls into the group of interior gateway protocols, operating within an autonomous system (AS)
The most widely-used interior gateway protocol (IGP) in large enterprise networks.
OSPF does not use TCP or UDP but uses IP directly, via IP protocol 89. OSPF handles its own error detection and correction, therefore negating the need for TCP or UDP functions.
BGP (Border Gateway Protocol)path vector protocolMakes routing decisions based on path, network policies and/or rulesets.
v4 supports Classless Inter-Domain Routing and the use of route aggregation to decrease the size of routing tables.
RFC 4271
The most widely-used exterior gateway protocol (EGP) is BGP.

Study for Exam #2

Leave a Comment