Enrutamiento de Origen

What Source Routing Enables

Source routing is an IP option that allows the sending host to specify the exact path — a sequence of intermediate routers — that a packet must traverse to reach its destination, rather than letting routers determine the path from their routing tablesA data structure stored in a router that lists known network destinations and the next hop or interface for reaching each one. Routing tables are populated by static configuration or dynamic routing protocols like BGP and OSPF.. IPv4 defines two variants: Loose Source Routing (LSR), where listed routers must be visited but other hops are permitted between them, and Strict Source Routing (SSR), where the packet must follow exactly the listed hops and no others.

Security Reasons for Blocking It

Source routing poses serious security risks. An attacker can use it to bypass FirewallA network security device or software that monitors and filters incoming and outgoing traffic based on predefined rules. Firewalls can block traffic by IP address, port number, protocol, or application-layer content. rules by routing packets through specific trusted intermediaries, impersonate internal addresses to probe networks, and conduct man-in-the-middle attacks by forcing traffic through a compromised router. For these reasons, virtually all modern routers and operating systems discard packets with source routing options by default. RFC 7126 recommends disabling IP source routing entirely.

Historical and Diagnostic Use

Despite its dangers, source routing was historically useful for network debugging — forcing test traffic along specific paths to isolate routing problems before TracerouteA network diagnostic tool that maps the path packets take from source to destination by sending probes with incrementing TTL values. Each responding router reveals one hop in the route, along with its latency. became ubiquitous. In modern networks, similar functionality is achieved safely through MPLSMultiprotocol Label Switching. A routing technique that directs data using short path labels rather than long network addresses, enabling fast, predictable traffic engineering across service provider networks. traffic engineering, which allows operators to specify explicit label-switched paths without exposing that capability to end users. Policy-Based RoutingA routing method that forwards packets based on criteria beyond the destination address, such as source IP, protocol, or port number. Used for traffic engineering, load sharing, and directing specific traffic through VPN tunnels. is the contemporary, administrator-controlled alternative for influencing packet paths.