Local versus remote assumption

From Citizendium, the Citizens' Compendium
Jump to: navigation, search
This article is developing and not approved.
Main Article
Related Articles  [?]
Bibliography  [?]
External Links  [?]
Citable Version  [?]
This editable Main Article is under development and not meant to be cited; by editing it you can help to improve it towards a future approved, citable version. These unapproved articles are subject to a disclaimer.

One of the early Internet architecture principles was called the local versus remote assumption, which means if a destination host is in the same Internet Protocol version 4 subnet as the host that wants to send to that destination, the two hosts will be on a shared medium, and will be able to reach one another using medium-specific addressing. If it is in a different (i.e., remote) subnet, you need to reach it via a router. These are reasonable assumptions with multiaccess broadcast media such as Ethernet/IEEE 802.3

This assumption has become flawed with partial mesh subnets over nonbroadcast multiaccess media (NBMA) like frame telay (FR) and asynchronous transfer mode (ATM), but still holds good for LANs and point-to-point lines. It has been necessary to develop workarounds, such as the inverse address resolution protocol (InARP) or next hop request protocol (NHRP) for NBMA media, or on media when a connection is set up only on demand (e.g., dialup).