Policy-based routing
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In computer networking, policy-based routing (PBR) is a technique used to make routing decisions based on policies set by the network administrator.
When a router receives a packet it normally decides where to forward it based on the destination address in the packet, which is then used to look up an entry in a routing table. However, in some cases, there may be a need to forward the packet based on other criteria. For example, a network administrator might want to forward a packet based on the source address, not the destination address. This should not be confused with source routing.
Policy-based routing may also be based on the size of the packet, the protocol of the payload, or some other characteristic. It can also be based on a combination of characteristics. This permits routing of packets originating from different sources to different networks even when the destinations are the same. This can be useful when interconnecting several private networks.
In the Cisco IOS, PBR is implemented using route maps.[1].
Linux supports multiple routing tables since version 2.2.[2]
Examples of PBR Usage
PBR can be used to redirect traffic to a proxy server by using a PBR-aware L3-switch (router). In such a deployment, specific source traffic (e.g. HTTP, FTP) can be redirected to a cache engine. This is known as virtual inline deployment.
References
- ^ Cisco IOS Release 12.0 Quality of Service Solutions Configuration Guide, http://www.cisco.com/en/US/docs/ios/12_0/qos/configuration/guide/qcpolicy.html
- ^ Linux Advanced Routing & Traffic Control HOWTO, http://www.tldp.org/HOWTO/Adv-Routing-HOWTO/index.html
3. http://www.ciscopress.com/content/downloads/cisco/bookreg/2237xxd.pdf