Policy-based routing
The term policy-based routing ( English policy-based routing , PBR ) refers to the routing of packets in which the forwarding decisions are made on the basis of policies . These policies are set by the network operator ; This means that, unlike metric- based routing, not only technical quality criteria but also strategic factors are taken into account.
Basic functionality
In metric-based routing, routers normally use a metric to decide which of several possible connections should be used when forwarding packets . Usually, the destination address is considered and then the connection with the lowest (e.g. transmission delay) or highest (e.g. bandwidth) value with regard to the metric is selected.
With policy-based routing, further criteria are taken into account, for example the source address, the packet size, the protocol or any other metadata . In this way, a more differentiated routing can be carried out, in which a different handling of packets with identical destination addresses is also possible. At the same time, the administrative effort increases. While the decisions in metric-based routing are made on the basis of simple properties, some of the policies have to be implemented using complex rules. This can also involve more complicated troubleshooting.
Application examples
An example of a policy-based routing protocol is the Border Gateway Protocol (BGP) for connecting autonomous systems (AS) on the Internet . In most cases, economic factors are used to choose the route. Internet service providers may be interested in treating through traffic between certain ASs separately, for example on the basis of existing contractual agreements.
Furthermore, policies can also be used to ensure quality of service .
See also
literature
- James F. Kurose , Keith W. Ross: Computer Networks ISBN 978-3-8273-7330-4 (standard work)
- Rolf Herheuser: Planning of switching networks: An introduction , vdf Hochschulverlag AG, 2008
Web links
- ITWissen.info: PBR (policy based routing) , accessed: March 12, 2014
- This is how Internet routing works: Router-Politik , Stefan Dierichs, Prof. Norbert Pohlmann, as of: September 15, 2008, accessed: March 12, 2014