Packet CRCs
Invariant CRC (ICRC)
Covers All Fields That Don't Change
The 32-bit ICRC is generated by the source CA port's Link Layer and covers all packet fields that do not change (i.e., they are not altered by switches or routers) as the packet transits from the source port to the destination port. The ICRC is present in all IBA packets but not in raw packets (in a raw packet the fields that may be altered while the packet is in transit are not known). The ICRC calculation is restarted for each new packet in a message.
The header fields that may be modified by switches or routers are comprised of:
The fields that a switch may modify as the packet transits the local subnet. This would include:
- LRH:VL.
- BTH:Resv8a fields. Note that although ...
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