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Zero Message Overhead Local Link Detection Mechanism Disclosure Number: IPCOM000022493D
Publication Date: 2004-Mar-18
Document File: 2 page(s) / 24K

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Zero Message Overhead Local Link Detection Mechanism

Proposed is a mechanism to assess whether a device is on the same link without using additional communication, but levering existing information stored in local data structures, like route tables or ARP tables, or properties of some classes of network addresses, like local link addresses.

Local Link Addressing (LLA) is defined as a method by which a host may automatically configure an interface with an IPv4 address in the 169.254/16 prefix that is valid for Link-Local communication on that interface. This is especially valuable in environments where no other configuration mechanism is available. [draft-ietf-zeroconf-ipv4-linklocal-09.txt]

Some protocols, e.g. liveness protocols, allow two types of communication: broadcast/multicast if the communicating nodes are on the same link, unicast if the communicating nodes are on different links. In the former case, in order to reduce the resource (memory) usage, the node that initiates the communication can avoid caching the local link destination addresses, because all the communication will be sent to a single broadcast/multicast address.

The protocols do not define a way of detecting whether two nodes are on the same link. Typically, a node can check if another node is on the same link by pinging using a protocol that do not cross routers (e.g. ARP – Address Resolution Protocol). Unfortunately, this requires additional communication, thus additional bandwidth usage and complexity. Especially in protocols that strive for being as lightweight as possible, this would result in a significant increase of the number of messages and of the complexity, at least of the device side.

A solution for this problem is based on leveraging some properties of other protocols and mechanisms, which are common in most of current network stacks. Especially we want to exploit the properties of LLA addresses and the information available in route tables at IP (Internet Protocol) level. Proposed is the following algorithm:

1 IF All addresses of NodeA interfaces are LLA addresses (in the range 169.254/16) THEN

2 NodeA considers that all addresses of other nodes are on the same link

3 NodeA does not store any address and only uses broadcast/multicast


5 NodeA parses its own route table and extract all the su...