deering@SU-PESCADERO.ARPA.UUCP (05/29/86)
Please excuse me if this has all been discussed to death in the past,
but I'm seeking the answers to the following two questions:
(1) Do any existing host or gateway implementations of IP ever decrement
the time-to-live field of a IP datagram by more than 1? I.e., does
anyone actually check for datagram holding times of more than one
second and adjust TTL accordingly?
(2) The IP spec (RFC791) says "...every module that processes a
datagram must decrease the TTL by at least one...". Is this
normally interpreted as including the originating host IP
module and/or the final destination host IP module?
-- Steve DeeringCLYNN@A.BBN.COM (05/29/86)
Steve, 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