These are used only when packets to be forwarded do not match any routing entry in an IP routing table. routes are manually configured by network administrators, have low system requirements, and apply to simple, stable, and small networks.

Default Routes

On the Internet, routers need to exchange routing information in the interconnection of networks called ______________ a collection of networks and subnetworks.

Autonomous Systems

The autonomous systems are connected together in the form of a network called the __________.

Core Network

Within AS, one network is connected to another network by an ___________.

Interior Gateway

The gateways that connect all the autonomous systems to the core network are called ____________.

Exterior gateways

It is meant to dynamically route data across a network that you fully control and maintain. Basically, it is meant to dynamically route data across a network that you fully control and maintain.

Interior Gateway Protocol (IGP)

This routing protocols are used to exchange routes between distinctly separate networks that you have no administrative control over.

Exterior Gateway Protocol (BGP)

determine good paths (routes) from senders to receivers through the network of routers.

Routing algorithms

the path with the smallest number of links between the source and the destination.

Shortest path

finds a path between the source and destination with the least cost.

Least-cost path

In this type of routing, all the routers send their routing tables to only their neighboring routers.

DISTANCE-VECTOR ROUTING PROTOCOL

In this type of routing, each of the routers sends the state of its own interfaces to all other routers only when there is a change to report.

LINK-STATE ROUTING PROTOCOL

the description of the router interface.

Link-State (LS)

the cost of sending data packets on the interface, expressed in the link state metric.

Output cost

these are other routers that are attached through the link-state.

List of neighboring routers

an OSPF data packet containing link-state and routing information that is shared with the other routers.

Link-State Advertisement (LSA)

a unit of data describing the local state of router's interfaces and adjacencies. The collected LS advertisements of all routers and networks form the LSDB.

Link-State PDU

a collection of all LS PDUs originated from the area's routers. Each router advertises directly-connected networks via LS PDU.

Link-State Database (LSDB)

This is a link-state routing protocol developed by the IETF in 1988 that is capable of quickly detecting topological changes within the autonomous system and establishing loop-free routes in a short period of time, with minimum additional communication overhead for negotiating topology changes between peering routers.

Open Shortest Path First (OSPF)

The OSPF area keyword identifies an OSPF area. This is considered a logical group, and each group is identified by an area ID.

Area

is the ISO name for a router. It is the communication between intermediate systems or routers.

IS (Intermediate System)

is a device on the network, such as a server or workstation. (Hosts)

ES (End System)

is a network service in the OSI stack

CLNS (Connection-Less Network Service)

is a Layer-3 address for CLNS packets. This is like an IP address in the TCP/IP stack. IS-IS uses NSAP addresses for communication, not IP addresses.

NSAP (Network Service Access Point)

contains information, such as the destination IP address, cost, and next-hop IP address, which guides packet forwarding.

OSPF routing table

This is a commonly used distance vector routing that uses its routing metric to determine the best route or shortest path a packet has to traverse from the source to a destination over a network. RIP is a distance-vector IGP and has a preference of 100.

Routing Information Protocol (RIP)

RIP uses a _____ as the route cost.

hop count

When a RIP routerstarts up, itsends a ________ to all of its neighbors to request routing information of the entire RIP network.

RIP request

also allows IP multicast packets for its announcements

RIPv2

uses IP broadcast packets for its announcements.

RIPv1

Important concepts about the relationship between OSPF routers:

neighbor relationship and adjacency

It is a special data packet (message) that is sent out periodically from a router to establish and confirm network adjacency relationships to other routers in the OSPF.

HELLO Packet

Routers that run a link-state routing protocol establish a neighbor elationship and then exchange Link State Advertisements, which indicate the devices’ presence with every interface port of a router.

Step 1. LSA Flooding

Each router generates LSAs and adds the received LSAs to its own link-state database (LSDB). Routers learn the whole network topology through the LSDB

Step 2. LSDB Creation

Each router uses the Shortest Path First (SPF) algorithm and LSDB information to calculate routes. Each router calculates a loop-free tree with itself as the root and the shortest path. L With this tree, a router determines the optimal path to each corner of a network.

Step 3. SPF Calculation

The router installs routes for the calculated preferred paths into its routing table.

Step 4. Routing Table Generation