IP Header (Cont)
Third word purpose: demuxing, error/looping control, timeout.
- Time to live (8 bits): Specified in router hops
- Protocol (8 bits): Next level protocol to receive the data: for de-multiplexing.
- Header checksum (16 bits): 1’s complement sum of all 16-bit words in the header.
- Change header => modify checksum using 1’s complement arithmetic.
Source Address (32 bits): Original source. Does not change along the path.