Subject to restrictions given below, a host MAY be able to act as an intermediate hop in a source route, forwarding a source-routed datagram to the next specified hop.
However, in performing this router-like function, the host MUST obey all the relevant rules for a router forwarding source-routed datagrams [INTRO:2]. This includes the following specific provisions:
|4 (Fragmentation Required but DF Set)||when a source-routed datagram cannot be fragmented to fit into the target network;|
|5 (Source Route Failed)||when a source-routed datagram cannot be forwarded, e.g., because of a routing problem or because the next hop of a strict source route is not on a connected network.|
To define the rules restricting host forwarding of source-routed datagrams, we use the term local source-routing if the next hop will be through the same physical interface through which the datagram arrived; otherwise, it is non-local source-routing.
A host is permitted to perform local source-routing without restriction.
A host that supports non-local source-routing MUST have a configurable switch to disable forwarding, and this switch MUST default to disabled.
The host MUST satisfy all router requirements for configurable policy filters [INTRO:2] restricting non-local forwarding.
If a host receives a datagram with an incomplete source route but does not forward it for some reason, the host SHOULD return an ICMP Destination Unreachable (code 5, Source Route Failed) message, unless the datagram was itself an ICMP error message.