Routers MUST implement the IP protocol, as defined by [INTERNET:1]. They MUST also implement its mandatory extensions: subnets (defined in [INTERNET:2]), IP broadcast (defined in [INTERNET:3]), and Classless Inter-Domain Routing (CIDR, defined in [INTERNET:15]).
Router implementors need not consider compliance with the section of [INTRO:2] entitled "Internet Protocol -- IP," as that section is entirely duplicated or superseded in this document. A router MUST be compliant, and SHOULD be unconditionally compliant, with the requirements of the section entitled "SPECIFIC ISSUES" relating to IP in [INTRO:2].
In the following, the action specified in certain cases is to silently discard a received datagram. This means that the datagram will be discarded without further processing and that the router will not send any ICMP error message (see Section [4.3]) as a result. However, for diagnosis of problems a router SHOULD provide the capability of logging the error (see Section [1.3.3]), including the contents of the silently discarded datagram, and SHOULD count datagrams discarded.