Source routing also gives malicious hosts the ability to influence packet routing. IPv4 already tried this with the LSRR/SSRR[1] options. The LSRR option was us

Source routing also gives malicious hosts the ability to influence packet routing. IPv4 already tried this with the LSRR/SSRR[1] options. The LSRR option was useful to malicious hosts for many purposes, such as[2]: o Bypass firewall rules. o Reach otherwise unreachable internet systems. o Establish TCP connections in a stealthy way. o Learn about the topology of a network. o Perform bandwidth-exhaustion attacks. Due to these "well-known security implications"[2], RFC 7126 recommends[3]: Routers, security gateways, and firewalls SHOULD implement an option- specific configuration knob to select whether packets with this option are dropped, packets with this IP option are forwarded as if they did not contain this IP option, or packets with this option are processed and forwarded as per [RFC0791]. The default setting for this knob SHOULD be "drop", and the default setting MUST be documented. [1] "{Loose/Strict} Source and Record Route" http://www.networksorcery.com/enp/protocol/ip/option003.htm http://www.networksorcery.com/enp/protocol/ip/option003.htm [2] https://tools.ietf.org/html/rfc7126#section-4.3.3 https://tools.ietf.org/html/rfc7126#section-4.3.3 [3] https://tools.ietf.org/html/rfc7126#section-4.3.5 https://tools.ietf.org/html/rfc7126#section-4.3.5