Interior Gateway Protocols (IGPs) 

Interior Gateway Protocols (IGPs) are routing protocols used within an autonomous system (AS). An AS is essentially a collection of IP networks and routers under the control of a single organization that shares a common routing policy. IGPs distribute routing information within their AS to determine the best path for transmitting data packets between networks.

There are several types of IGPs:

RIP (Routing Information Protocol):

  • TypeDistance-vector protocol.
  • MetricUses hop count as its metric, with a maximum of 15 hops.
  • VersionsRIP version 1 (RIPv1) and version 2 (RIPv2). RIPv2 supports VLSM (Variable Length Subnet Masking) and multicast for routing updates.
  • ConvergenceCan be slow, leading to loops in certain cases.
  • UsageDue to its limitations, RIP is less common in modern networks but might be found in simpler or older networks.

EIGRP (Enhanced Interior Gateway Routing Protocol):

  • TypeAdvanced distance-vector (often termed as a hybrid protocol because it has characteristics of both distance-vector and link-state protocols).
  • MetricUses a composite metric based on bandwidth, delay, reliability, and load.
  • FeaturesSupports fast convergence using Diffusing Update Algorithm (DUAL).
  • ScalabilityScales well in large networks.
  • ProprietaryOriginally a Cisco proprietary protocol but now it’s an open standard.

OSPF (Open Shortest Path First):

  • TypeLink-state protocol.
  • MetricUses cost, which is inversely proportional to bandwidth.
  • FeaturesDivides large networks into areas for better scalability and management. Uses Dijkstra’s algorithm to compute the shortest path tree.
  • ConvergenceFaster than RIP.
  • UsageOne of the most widely used IGPs in larger networks.

IS-IS (Intermediate System to Intermediate System):

  • TypeLink-state protocol.
  • MetricUses cost like OSPF.
  • OperationWorks on the data link layer, making it unique as it doesn’t rely on IP. Instead, it uses CLNP (Connectionless Network Protocol).
  • UsageCommonly used by telecommunications providers.

Key Concepts Associated with IGPs:

  • ConvergenceHow quickly the routers in a network update their routing tables and come to a consensus about the network topology after a change.
  • MetricA standard by which the protocol determines the best path for data. Different protocols use different metrics.
  • Distance VectorProtocols that use distance (metric) and direction (vector) to decide the best path. They send their routing tables to their direct neighbors.
  • Link-StateProtocols that create a complete map of the network to compute the best path.

Each IGP has its strengths and weaknesses, and the choice of which one to use often depends on the specific requirements of the network in question.

Key terms in plain language

Open a term for a concise explanation of language used on this page.

Bandwidth

The amount of data a connection can carry in a given time, usually measured in Mbps or Gbps. More bandwidth supports more users, devices, and simultaneous applications.

Cloud Computing

Computing resources—such as applications, servers, storage, or databases—delivered from remote infrastructure and scaled as requirements change.

Infrastructure as a Service (IaaS)

Cloud-based servers, storage, and networking that customers configure and manage without owning the underlying data-center hardware.

Software as a Service (SaaS)

Software accessed as an online service instead of being installed and maintained entirely on the customer’s own computers or servers.

Disaster Recovery (DRaaS)

A plan and service for restoring applications, data, and operations after an outage or disruption. DRaaS provides recovery infrastructure through a managed cloud service.

Identity and Access Management (IAM)

The systems and policies that determine who a user is, what resources they may access, and how that access is authenticated and reviewed.