1. Lecture #2 VLSM Asst.Prof. Dr.Anan Phonphoem Department of Computer Engineering, Faculty of Engineering, Kasetsart University, Bangkok, Thailand

2. Outline VLSM

3. Variable-length subnet mask Classful allows only one subnet in a network > one subnet in an autonomous system Maximizing the use of address (Subnet Zero) “Subnetting a Subnet” Routing that support VLSM OSPF, Integrated IS-IS, EIGRP, RIPv2, and static routing

4. Subnet with VLSM 192.168.10.0/24

5. Subnet with VLSM Select the biggest first 192.168.10.0/24 192.168.10.0/26 192.168.10.64/26 192.168.10.128/26 192.168.10.192/26 192.168.10.64/26 192.168.10.64/27 192.168.10.96/27 192.168.10.128/27 192.168.10.192/27 Perth KL

6. Subnet with VLSM 192.168.10.96/27 192.168.10.96/28 192.168.10.112/28 192.168.10.224/28 192.168.10.240/28 192.168.10.224/28 192.168.10.128/30 192.168.10.132/30 192.168.10.136/30 192.168.10.140/30 Sydney Singapore Perth – KL Sydney – KL Singapore – KL

7. Subnet with VLSM

8. Assignment CPEIE EE 165.23.220.0/20 700 Stations 500 Stations100 Stations 250 Stations

9. Solution 165.23.220.0/20 165.23.208.0/22 165.23.212.0/22 165.23.216.0/22 165.23.220.0/22 165.23.212.0/22 165.23.212.0/23 165.23.214.0/23 165.23.214.0/24 165.23.215.0/24 165.23.215.0/25 165.23.215.128/25 165.23.215.128/30 165.23.215.132/30 165.23.215.136/30 … 1022 Hosts 510 Hosts 254 Hosts 126 Hosts 2 Hosts

10. Solution CPEIE EE 165.23.220.0/20 700 Stations 500 Stations100 Stations 250 Stations 165.23.208.0/22 165.23.214.0/24 165.23.215.128/30165.23.215.132/30 165.23.212.0/23165.23.215.0/25

11. Route Aggregation Route summarization Supernetting Possible only if routers of a network use a classless routing protocol (OSPF or EIGRP) Carry 32-bit IP address and bit mask in the routing updates Share the same high-order bits

12. Routing Protocols Autonomous systems (AS) generally administered by a single entity Each AS has a routing technology which can differ from other autonomous systems Interior Gateway Protocol (IGP) Routing in the AS Exterior Gateway Protocol (EGP) transfer routing information between autonomous systems

13. RIP work as an IGP in a moderate-sized AS RIPv1 is classful IGP distance vector protocol Use hop count as a metric Route update is 30 sec (Broadcast) load balancing upto 6 paths

14. RIPv2 allows it to send out subnet mask information with the route update provides for authentication in its updates multicasts routing updates (224.0.0.9)