Re: time-to-live

29 May 1986 09:56-EDT

        The TOPS-20 IP implementation does decrement the Time-to-live
field by more than one if the packet has been queued for more than a
second. Note however, that this doesn't really apply to the major
source of output-queue delay which is in the layer(s) below IP. The
timeout for received fragments is set from the time-to-live field, but
any additional fragment which is received will reset the timeout to
allow fragments from different retransmissions to be combined.

        The TOPS20 always decrements the Time-to-live, even when it is
the originating or receiving host (since the systems support multiple
network interfaces and will typically forward packets, route loops could
theoretically occur). When a packet is received with a Time-to-live
of 1, the packet will be delivered to the higher layers, but not forwarded.

Charles Lynn

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