Cisco® CCNA Exam Cram Notes : Routed and Routing Protocol

III. Routing Technologies

1. Routed and Routing Protocol

Routed Protocol: A Routed Protocol is a computer network protocol that can be used to send the user data from one network to another network. Routed Protocol carries user traffic such as e-mails, file transfers, web traffic etc.

Routed protocols use an addressing system (example IP Address) which can address a particular network and a host (a computer, server, network printer etc) inside that network. In other words, the address which is used by a Routed Protocol (Example IP (Internet Protocol)) has a network address part and a host (a computer inside a network) part.

IP (Internet Protocol) is the most widely used Routed Protocol. Internet is using IP (IPv4 or IPv6) as its Routed Protocol. A Routed Protocol is an integral part of network protocol suit (such as TCP/IP protocol suit) and is supported by the networking devices (such as routers, switches, and host computers) participating in routing the user traffic.

Routing Protocol : A Routing Protocol learns routes (path) for forwarding a Routed Protocol such as IP (Internet Protocol), IPX (Internetwork Packet Exchange) and Appletalk. Routing Protocols are network protocols used to dynamically advertise and learn the networks connected, and to learn the routes (network paths) which are available. Routing protocols running in different routers exchange updates between each other and most efficient routes to a destination. Routing Protocols maintain routing tables that contain paths to a destination network node computed according to routing algorithms. Routing Protocols normally run only in Routers, Layer 3 Switches, End devices (firewalls) or Network Servers with Network Operating Systems. Routing Protocols are not available in a user computer.

Examples of Routing Protocols are RIP (Routing Information Protocol) , EIGRP (Enhanced Interior Gateway Routing Protocol) and OSPF (Open Shortest Path First).

RIP-enabled routers on a TCP/IP internetwork broadcast their complete routing tables every 30 seconds over User Datagram Protocol (UDP) using RIP advertisements. RIP does not support multipath routing. If a routing table has multiple routes for a single network ID, RIP stores the route with the lowest metric (number of hops to destination). RIP supports a maximum metric of 15; networks that are more than 15 hops away are unreachable using RIP.

Routing tables in RIP-enabled routers are calculated on the basis of the number of hops to the destination network. RIP routers do not use other routing metrics such as load, bandwidth, latency, or Maximum Transmission Unit (MTU) in calculating routing costs. The routing table of a RIP router contains the cost in number of hops of every path to every destination network in the internetwork.

IP Packets are transported from source network to the destination network by what is known as routing. Hop-by-hop routing model is used by the Internet for delivery of packets. At each hop, the destination IP address is examined, the best next hop is determined by the routing protocol (such as RIP, OSPF or BGP) and the packet is forwarded by one more hop through this route. The same process takes place at the next hop. During this process, the logical addresses remain same. In an IP network, the logical addresses are IP addresses. The hardware interface addresses, such as MAC address change with each hop.


An administrative distance of 0 represents highest trustworthiness of the route.
An administrative distance of 255 represents the lowest trustworthiness of the route.

The below table default administrative distances.

default administrative distances

Originating source port numbers are dynamically assigned by source host, usually greater than 1023.

Numbers 0 - 255 are used for public applications

Numbers 255 - 1023 are assigned to companies so that they can use these port numbers in their applications.

Numbers above 1023 are used by upper layers to set up sessions with other hosts and by TCP to use as source and destination addresses.

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