This is correct however this is not how it is implementing in 99% if routers as it is to hard and time consuming.
The normal method of implementing this TTL field is to decrement this field by one as it passes through the router. No need to worry about checking time etc. IF the TTL field hit zero after the router decrements it, drop the packet! -----Original Message----- From: EXT Russell Coker [mailto:[EMAIL PROTECTED] Sent: 10. March 2000 22:54 To: [EMAIL PROTECTED]; [email protected] Subject: Re: Strange Network Problem (TTL?) On Fri, 10 Mar 2000, Chris Wagner wrote: >At 11:41 PM 3/9/00 +0100, Paul van Empelen wrote: >>Time to live has nothing to do with time, although the name suggests it. >>It is a hop count. You start at e.g. 255. On the next hop the IP packet >>will have a ttl of 254 and so on. > >So it's really a max hops limit. How did it get a name like TTL?? What >function does it serve? Besides providing a mechanism to expire lost >packets... What role does each host's TTL setting play in a ping or trace? If you have a packet in your network buffers for 1 second you should decrement the TTL. That way a packet can survive on the net for a maximum of 255 seconds. This is why there are ~4 minute timeouts on some parts of TCP. Here is the relevant section from rfc791. If you have installed the doc-rfc package you'll have this on your system. Time to Live: 8 bits This field indicates the maximum time the datagram is allowed to remain in the internet system. If this field contains the value zero, then the datagram must be destroyed. This field is modified in internet header processing. The time is measured in units of seconds, but since every module that processes a datagram must decrease the TTL by at least one even if it process the datagram in less than a second, the TTL must be thought of only as an upper bound on the time a datagram may exist. The intention is to cause undeliverable datagrams to be discarded, and to bound the maximum datagram lifetime. As for the so-called "open DNS". What is the point of blocking TCP port 53? If information is private then don't publish it in the DNS!!! -- My current location - X marks the spot. X X X -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
