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Source routing

Source routing

(also path selection, source route)

Source routing definition

Source routing is a technique in which the sender specifies the route the data packet will take through the network. In conventional IP routing, each router in the path determines the next hop based on its routing table. In source routing, the sender predetermines the entire path.

See also: segment routing

Types of source routing

  • Strict source routing (SSR). The packet travels through the exact sequence of routers specified by the sender. The packet will be dropped if one of the routers in the sequence is unreachable or the specified path is invalid.
  • Loose source routing (LSR). The packet travels through a series of routers specified by the sender but not always in direct succession. The packet may pass through other routers in between the specified ones.

Uses of source routing

  • Testing and troubleshooting. Network administrators use source routing to test specific paths through a network or diagnose issues.
  • Bypassing normal routing. Suppose an administrator aims to avoid congestion, optimize a path for a specific traffic, or perform other troubleshooting tasks. In that case, they may force a packet to bypass the default routes determined by routing protocols.
  • Load balancing. Although not an optimal technique in this case, source routing can distribute traffic among multiple paths in the network.

Security risks

  • Spoofing and eavesdropping. Malicious actors use source routing to route their packets to intercept or eavesdrop on data traffic.
  • Bypassing security measures. If firewalls or other security devices are not correctly configured to inspect and potentially drop source-routed packets, malicious traffic could bypass these security measures.

Further reading

Ultimate digital security