VLSM /CIDR
VLSM: VARIABLE LENTGH SUBNET MASK
CIDR: CLASSLES INTERDOMAIN ROUTING
SO IF YOU HAVE A NETWORK COMPOSED OF "X" NUMBER OF SUBNETWORKS YOUR ARE USING VLSM, WHY?? THE REASON YOU ARE SUBNETTING A SINGLE CLASS A,B,C MOTHER NETWORK, INTO MULTIPLE DAUGHTER SUBNETS DEPENDING ON THE NEEDS OF YOUR HOSTS OR NETWORKS.
NOW. THAT YOU HAVE SUBNETTED A SINGLE CLASS C (/24)FOR EXAMPLE INTO MULTIPLE CLASS (/30) FOR THE WANS, AND (/28) SUBNETS FOR THE REMOT LANS, NOW THERE IS A NEED FOR ROUTING BETWEEN THEM.
THERE IS WHERE CIDR COMES THROUGH.
IF YOU PLAN TO ROUTE USING STATIC ROUTING, THEN THERE IS NO PROBLEM, BUT IF YOU WANT TO USE DYNAMIC ROUTING, THERE ARE SOME DYNAMIC ROUTING PROTOCOLS THAT TO NOT ROUTE SUBNETS UNLESS THEY BELONG TO THE DEFAULT MASK CLASS NETWORKS, FOR EXAMPLE:
RIP, IGRP ARE CLASSFUL AND ONLY ROUTE NETWORKS BELONGING TO A CLASS A,B,C .
EIGRP, OSPF ARE CLASSLESS, THEY ROUTE SUBNETS THAT YOU HAVE ALREADY SUBNETED FROM THE SINGLE CLASS C (MOTHER) NETWORK.
IT DOES IT BY CARRING INT THE ADVERTISEMENTS INFORMATION ABOUT THE MASK THAT INDENTIFIES THE SUBNET.
SALUTE! HOPE IT HELPS YOU.
:twisted:
HAVOHEJ CCIE
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