Hi Sandipan,
A discontiguous network is:
A major network that is separated by another major network.
In this figure subnetwork of major network 172.20.0.0 separates major network 172.16.0.0.
172.16.0.0 is therefore a discontiguous network.
172.16.0.0 would be a contiguous network if there was for example network 172.16.4.0/24 between Router1 and Router2 instead of 172.20.88.0/24.
The problem with discontiguous networks comes up when you are using routing protocols such as RIPv1, IGRP or EIGRP with auto-summary. If you want to know more please don't hesitate to ask.
For more information about RIPv1,IGRP and problem with discontiguous networks, please check this link:
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093fd6.shtml
The figure is also from that document.
Best regards,
Jan
