10. Understanding IP Requirements
• Subnetworks on the LAN/WAN need to be
issued using perfect powers of 2
• 22 = 4
• 23 = 8
• 24 = 16
• 25 = 32
• 26 = 64
• 27 = 128
11. Scaling Subnets
• With a requirement of 23 nodes…
• The next perfect power of 2 that meets
this need = 32
• 25 = 32 5 host bits needed
• Last Octet is then represented as:
– A.B.C.NNNHHHHH N=Network H=Host
– 11111111.11111111.11111111.11100000
15. Reference Points
• Use numbers, symbols, letters to represent
each LAN / WAN link
• Use some consistent method for assignment
– Size of Subnetwork
– Location
– Zone or Distribution Point
19. VLSM and Routing Protocols
• Does your routing protocol support varying
the length of the subnet mask from one
interface to another?
• Can you re-subnet a subnet differently
from one interface to another and still
advertise that subnetwork via RIPv1,
RIPv2, OSPF, EIGRP, ISIS, BGP?
24. Problem!
• The 192.168.20.0 /24 network gives us:
– 1 Network
– 254 Nodes Available for Assignment
• 13 Subnetworks Required
• Network Demands range from 4 – 32
nodes per LAN / WAN segment
51. Future Expansion Danger
• Note the three locations with the and
• If we need to add a network printer or visitor
with laptop, the IP addressing scheme will have
to be modified.
• This results in downtime and careful migration
planning
There must be a better way!
