1. Subnetting the subnet RD-CSY2001-2008/09

2.  Company with 200 hosts  Assigned class C network 195.10.1.0/24  Want 6 different LANs  Subnet class C network using mask 255.255.255.224 (/27)  Whole network has the same subnet mask or supports equal number of hosts on all the sub-networks ◦ Is this a problem? ◦ Why? ◦ What should be done to solve it ? RD-CSY2001-2008/09

3.  VLSM Subnets a subnet ◦ VLSM divides a network into subnets of various sizes to prevent wasting IP addresses  Uses up wasted addresses  Conserves address space on WAN links  Point-to-point link only needs 2 addresses  With VLSM point-to-point links can use a /30 mask RD-CSY2001-2008/09

4.  Variable Length Subnet Masking allows division of address space based on the size of networks ◦ Start with network requiring the most addresses ◦ Create a subnet mask  (use CIDR – Classless Inter Domain Routing) ◦ Subnet the subnet as needed to provide address space required for other subnets  Be logical – start at beginning or end or address space  Addresses must be contiguous to enable route summarization RD-CSY2001-2008/09

5. Question  If an ISP has a 200.1.1.0 Network, he wants to give assign to 5 customers who need 20, 12, 6, 25, 18 hosts. ◦ What should the subnet mask be? ◦ What is the address range in each subnet? ◦ What should the routing table entries be? ◦ Can it be done efficiently to conserve IP addresses? RD-CSY2001-2008/09

8.  Address format.  The prefix denotes the upper P bits of the IP address.  Can be used to specify arbitrary blocks of addresses ◦ Say an ISP has 192.5.48.0, 192.5.49.0,192.5.50.0,192.5.51.0 then ◦ the IP address advertised will be 192.5.48.0/22  An ISP can obtain a block of addresses and partition this further to its customers  Say an ISP has 200.8.4/24 address (256 addresses) ◦ He has another customer who needs only 4 addresses from 200.8.4.24 then that block can be specified as 200.8.4.24/30 RD-CSY2001-2008/09

9. Given IP address 204.15.5.0/24, use VLSM to create a subnetting scheme

10. Please try other questions on VLSM, available on module web page RD-CSY2001-2008/09