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IP Scheme Design

IP Scheme should be simple and summarizeable

Joseph W. Doherty
Hall of Fame Expert


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The original purpose of IP addresses is to provide a physical unique identification for delivery of packets.  To allow scalability, the IP address is split into a network number and a host number.  To allow even larger scalability, network numbers are aggregated, sharing the same binary prefix, to reduce routing table sizes.  Both networks and aggregated networks are generally tied to the physical topology.

In addition to using IP addressing to deliver packets on networks, network numbers have often been used for some type of access control.  The latter is what causes problems when an IP address that's more or less required to represent some location in the physical topology is also used for some kind of role control.  E.g. network 5 contains our servers, network 6 contains sales agents, or network 50 for data and network 51 for VoIP.

With laptops, user roles can't as easily be tied to a network number, and likewise, be used for something like a software based VoIP phone on a PC.

Consider using IP addressing just for L3 topology purposes, and some other method for role/use identification.  I would suggest you discard your 3 options and think "outside the box".  How might you "identify" data, VoIP and/or video without using IP addressing?

Jeff Van Houten

From a security perspective Cisco would recommend something closer to #1 so you can acl the voice (and video??) separately from the data.

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