Elements of Computer Networking: An Integrated Approach (Concepts, Problems and Interview Questions) by Narasimha Karumanchi & Damodaram A & Sreenivasa M

Author:Narasimha Karumanchi & Damodaram A & Sreenivasa M [Karumanchi, Narasimha]
Language: eng
Format: epub
Publisher: CareerMonk Publications
Published: 2016-12-20T08:00:00+00:00

8.9.3.1 Point-to-point networks

A point-to-point network is a link between exactly two routers. A packet sent from one of the routers will always have exactly one recipient on the local link.

8.9.3.2 Broadcast multi-access

Point-to-point links don’t scale well. A much more efficient manner of connecting a large number of devices is to implement a multi-access segment. Multi-access segment is a segment which can be accessed by multiple end points. An Ethernet segment is an example of such a network.

Ethernet networks support broadcasts; a single packet transmitted by a device can be multiplied by the medium (in this case an Ethernet switch) so that every other end point receives a copy. This is advantageous not only in bandwidth savings, but also in facilitating automatic neighbour discovery.

In the example above, Router-1 can multicast (a broadcast intended only for certain recipients) an OSPF hello message to the link, knowing that all other OSPF routers connected to the link will receive it and reply with their own multicast message. Consequently, neighbours can quickly identify each other and form adjacencies without knowing addresses beforehand.

OSPF routers on a multi-access segment will elect a designated router (DR) and backup designated router (BDR) with which all non-designated routers will form an adjacency. This is to ensure that the number of adjacencies maintained does not grow too large.

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