Automatic Subnet Numbering Hilarie Orman

Layer Addressing Characteristics Unique, uncorrelated addresses Linear strings of nodes Join points Spanning tree Layer 3 Address blocks grouped by contiguous bits Mesh of routers Configured topology over layer 2 Universal address space

Routers and Subnets without IP addrs, no routing X X X X X

IP Address Fixed prefix ARIN or non-routable Subnet number Host number DHCP

X X X X X SubnetNumbers SUBNET 7 SUBNET8 SUBNET 5 SUBNET 6 SUBNET 4

Requirements Support initialize, join, leave, partition, rejoin Utilize IPv4 addresses efficiently Solve v6 and v4 assignments Cooperate with DHCP Minimal interference with ongoing end node connections Be secure

X Central Authority Single point of failure Request Subnet Number X Reply Subnet Number Single point of failure --- ameliorate with elections

Distributed Agreement Protocol X X X Router 1 needs 3 subnet numbers X Router 2 needs 2 subnet numbers X

Distributed Protocol Problems Might be slow at startup Partitions due to failure require renumbering Partition joins as part of network growth would be complicated Authentication … via secure multicast keying?

Network Partition / Nodes Join SUBNET 7 SUBNET 1 SUBNET 10 X SUBNET8 X SUBNET 2 X SUBNET 9 X SUBNET 3 X SUBNET 10 X SUBNET 4

X X X Node Mobility Prefix | subnet 1 | hostnum

Address Utilization Mobility makes subnet size difficult to predict Simplest assignment method divides address space into N subnets of equal size Must overprovision and waste Dynamic subnet size adjustment Difficult to synchronize

Automatic Numbering at Layer 3 Main Points No end node mobility without mobile IP Partition/rejoin might require reassigning end node addresses Breaks connections Sizing subnets is awkward