Source routing

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Source routing (abbr .: SR) is a route selection technique with which the sender node can determine a complete route sequence to the destination node. This procedure is the specification of a routing algorithm at the LLC level .

overview

It is a complementary method to the Spanning Tree Protocol . This makes it possible to identify redundant structures. Source routing and spanning tree differ in the information storage required to transport a data packet from the sender to the destination station. The source designates the sender who specifies the route that a packet should take. This means that the bridge does not hold the information about the route of the data packet , but rather the sending station handles the routing tables for all open (active) connections.

The term "source routing" is used both for Token-Ring networks and for special options of IP . Source routing on Token-Ring networks is also a method for route selection in the case of redundant paths between Token-Ring switching elements ( bridges ) and uses the different broadcast bits in the head of the LLC frame. Knowledge of the details of the functionality (broadcast variants SRE versus ARE , hop count limit, spanning tree implementation of path costs) is essential for the optimal design of large token ring networks .

Details

The following options are set in the option field of the IP header :

  1. Strict Source Routing (Option 9 RFC 791 ): A maximum of 9 route nodes are defined behind the option field, which must be passed through. This is a fixed route.
  2. Loose Source Routing (option 3 RFC 791 ): A maximum of 9 route nodes are defined behind the option field, which must be passed through. It doesn't determine the entire route.

The "Record Route" option is closely related to the source routing. If this option is set, each node passed through adds its IP (maximum 9) to the specified field behind the option field.

A source route is static if all routes are statically defined. A source route is dynamic if all routes are generated dynamically and changed after changing the topology .

safety

Source routing is a security concern: a sniffer can enter its IP address in the routing field and thus receives all packets for its host. Many firewalls and routers therefore discard these packets.

See also

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