Internet Cache Protocol (ICP)

Common Header

Name Size (bytes) Description
opcode 1 Numeric code indicating type of message
version 1 Version of the protocol being used
length 2 Total length of packet
reqnum 4 Request number assigned by client
authenticator 8 Authentication information (future)
senderid 4 Identification (host id) of sender

Message Types

Opcode Name Description
1 Query Query a cache to determine hit/miss
2 Hit Cache has a copy of the queried object
3 Miss Cache does not have a copy of the queried object
4 Err Some type of error occurred at the server
5 Send Send object to client (retrieve if necessary)
6 SendA Send/validate object to client (retrieve if necessary)
7 DataBeg Denotes the beginning of object data
8 Data Denotes the next segment of object data
9 DataEnd Denotes the final segment of object data