This is the ability to severaly subnet your intial block of IP addresses to smaller usage networks)subnets). This is don by borrowing subnet bits from the host part of the IP address block. It is mostly required if you have many serial/WAN connections or better still you want to properly seperate your network for precise management/troubleshooting purposes. eg for a block of IP address as this 216.72.67.0 255.255.255.0
If you have a router with say two interfaces and circumtances require that we give each interface a global IP address. Without VLSM =Variable Length Subnet Mask, you would not be able to achieve this from the above given IP address block. VLSM saves you the problem of requesting for another IP address block. Now to be able to name my roouter interfaces(2), I will have to borrow 6 bits from the host part , that would give (128+64+32+16+8+4=252) ie (256-252=4 IP addresses per subnet, only 2 usable, the 1st is network address(unusable) and the other is broadcast address (unusable)). Your two interfaces could then be named as: inf1=216.72.67.1 255.255.255.252 to 216.72.67.3 255.255.255.252 inf2=216.72.67.5 255.255.255.252 to 216.72.67.7 255.255.255.252 Coninue in steps of 4 to name other networks, however if you no longer have other networks you can revert back to something like: 216.72.67.9 255.255.255.0 216.72.67.10 255.255.255.0 216.72.67.11 255.255.255.0 etc for host addresses Rememebr only routing protocols that supports CIDR would be able to rout your networks. Go to www.cisco.com to learn more. Regards. Oletu ----- Original Message ----- From: Tel Khan To: Sent: Thursday, November 29, 2001 4:35 AM Subject: Help on VLSM [7:27665] > Hi folks, > > I dont fully undertand VLSM i have read this in the Sybex book and i'm still > at a loss, I would be grateful for some guideness. > > Sorry for beeing thick! > > Regards > Tel _________________________________________________________ Do You Yahoo!? Get your free @yahoo.com address at http://mail.yahoo.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=27753&t=27665 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
