Distributed VLAN mechanism for packet field replacement in a multi-layered switched network element using a control field/signal for indicating modification of a packet with a database search engine

A method for selectively performing header field replacement in a network switch device comprising the steps of:

• an input port process (IPP) buffering an input packet and providing a copy of a header associated with the input packet to a search engine;
• the search engine searching a database to determine a type of the input packet and notifying the IPP of the type of the input packet;
• the IPP selectively replacing at least one field in the header in response to the information provided by the search engine and selectively outputting control field information to indicate the need for additional modification of the modified input packet prior to output from the network switch;
• an output port process (OPP) reading the modified input packet and corresponding control field information from the IPP, the OPP stripping a cyclic redundancy code (CRC) associated with the input packet and selectively generating at least one control signal to an output interface to indicate that the modified input packet is to be further modified prior to output from the network switch and to output the selectively modified input packet;
• the output interface outputting the modified input packet further selectively modified in response to the at least one control signal received from the OPP by selectively modifying at least one header field and regenerating the CRC based upon the modified input packet.

In a packet switch, an apparatus for selective header field replacement comprising:

• a switch element including an input port process (IPP), a database, a search engine, an output port process (OPP), and a media access controller (MAC), the IPP coupled to the MAC and the search engine the IPP receiving from the MAC header information associated with an input packet comprising a header, data and a cyclic redundancy code (CRC), the database configured to store information to facilitate forwarding and filtering of packets, the search engine coupled to the database and coupled to receive a copy of the header from the IPP, the search engine configured to search the database to determine and supply information regarding a type of the input packet and information regarding the input packet'next hop to the IPP which is configured to selectively replace at least one field in the header responsive to the type and to selectively output control field information to the OPP to indicate the need for additional modification of the input packet prior to output from the packet switch;
• if the type determined by the search engine indicates that the header does not change, the input packet is output from the packet switch without modification thereby preserving end-to-end error robustness;
• if the information determined by the search engine indicates that at least one portion of the header changes, the header of the input packet is updated by the IPP, the CRC is stripped by the OPP and regenerated by the MAC based upon the updated packet and the updated packet is output from the packet switch.

In a packet switch, an apparatus for selective header field replacement comprising:

• an input port process (IPP) configured to receive a packet comprising a header, data and cyclic redundancy code (CRC) and configured to selectively replace at least one field in the header in response to information regarding a type of packet and selectively output control field information to indicate additional modification of the packet prior to output from the switch;
• an output port process (OPP), coupled to the IPP, configured to receive the packet and the control field information, the OPP configured to selectively generate at least one control signal to indicate that the packet is to be further modified prior to output from the switch and to output the packet;
• and
• a media access controller (MAC) coupled to receive the at least one control signal and the packet, the MAC configured to transmit an output packet corresponding to the selectively modified packet, in response to the at least one control signal, the MAC further configured to selectively modify at least one header field and the CRC prior to transmission of the output packet.