Abstract: Embodiments of the apparatus for modifying packet headers relate to a packet generalization scheme that maintains information across protocol layers of packets. The packet generalization scheme uses a protocol table that includes layer information for all possible protocol layer combinations. The protocol layer combinations in the protocol table are manually configured through software. Each protocol layer combination in the protocol table is uniquely identified by a PktID. A rewrite engine of a network device receives the PktID for a packet and uses that unique identifier as key to the protocol table to access information for each protocol layer of the packet that the rewrite engine requires during modification of the packet. The packet generalization scheme eliminates the need for a parser engine of the network device to pass parsed data to the rewrite engine, which is resource intensive.

Abstract: Embodiments of a leaky bucket model relate to simulation of a MAC (media access control) to enable verification of a core logic and the MAC without the MAC being physically available. The simulated MAC is typically implemented on a computing device that is in communication with the core logic and a SerDes (serializer/deserializer). The simulated MAC uses a leaky bucket model to determine behavior of the core logic and the MAC.

Abstract: Embodiments of the apparatus for modifying packet headers relate to a use of bit vectors to allow expansion and collapse of protocol headers within packets for enabling flexible modification. A rewrite engine expands each protocol header into a generic format and applies various commands to modify the generalized protocol header. The rewrite engine maintains a bit vector for the generalized protocol header with each bit in the bit vector representing a byte of the generalized protocol header. A bit marked as 0 in the bit vector corresponds to an invalid byte, while a bit marked as 1 in the bit vector corresponds to a valid byte. The rewrite engine uses the bit vector to remove all the invalid bytes after all commands have been operated on the generalized protocol header to thereby form a new protocol header.

Abstract: Embodiments of the apparatus for modifying packet headers relate to programmable modifications of packets by applying commands to generalized protocol headers. Each protocol header of incoming packets is represented in a generic format specific to that protocol to enable modifications to packet headers. Missing fields from a protocol header are detected, and the protocol header is expanded to a maximum size such that the protocol header contains all possible fields of that protocol, including the missing fields. Each of the fields has the same offset irrespective of which variation of the protocol the protocol header corresponds to. Modification uses a set of commands that is applied to expanded protocol headers. All of the commands are thus generic as these commands are independent of incoming headers (e.g., size and protocol).

Abstract: Embodiments of the apparatus for modifying packet headers relate to a rewrite engine that represents each protocol header of packets in a generic format specific to that protocol to enable programmable modifications of packets, resulting in hardware and software flexibility in modifying packet headers. Software programs generic formats in a hardware table for various protocols. The rewrite engine is able to detect missing fields from a protocol header and is able to expand the protocol header to a maximum size such that the protocol header contains all possible fields of that protocol. Each of the fields has the same offset irrespective of which variation of the protocol the protocol header corresponds to. The expanded protocol header is represented by a data structure that is independent of a size of the protocol header.

Abstract: Embodiments of the apparatus for modifying packet headers relate to pointer structure for splitting a packet into individual layers and for intelligently stitching them back together. The pointer structure includes N+1 layer pointers to N+1 protocol headers. The pointer structure also includes a total size of all headers. A rewrite engine uses the layer pointers to extract the first N corresponding protocol layers within the packet for modification. The rewrite engine uses the layer pointers to form an end point, which together with the total size of all headers is associated with a body of the headers. The body of the headers is a portion of headers that are not modified by the rewrite engine. After all the modifications are performed and modified headers are compressed, the modified layer pointers are used to stitch the modified headers back together with the body of the headers.

Abstract: Embodiments of the apparatus for modifying packet headers relate to a rewrite engine that represents each protocol header of packets in a generic format specific to that protocol to enable programmable modifications of packets, resulting in hardware and software flexibility in modifying packet headers. Software programs generic formats in a hardware table for various protocols. The rewrite engine is able to detect missing fields from a protocol header and is able to expand the protocol header to a maximum size such that the protocol header contains all possible fields of that protocol. Each of the fields has the same offset irrespective of which variation of the protocol the protocol header corresponds to. In a bit vector, all newly added fields are marked invalid (represented by 0), and all existing fields are marked valid (represented by 1). Software modification commands allow data to be replaced, removed and inserted.