basic questions

Just for the record, there are more TTL's.

TTL for tcp traffic is based on hops allowed.
TTL for DNS e.g. is based on time.

Ok, just read the book of all TCP/IP and apparently the TTL was originally designed to contain a time value (in seconds), which would be filled in when the datagram was originally sent. Routers then decrese the value periodically. Since routers can handle the transfer of datagrams faster than a second, this wasn't seen to be a good way which is why its used for Hop Count.

The TTL filed was also designed to ensure time-critical datagrams wouldn't become stale or pass their expiration date.

That doesn't sound right to me. How would router 2 know what time the packet left router 1? Unless I'm missing something about regular data packets having timestamps in them...

Hmm, what if the router timestamped the packets only internally? could that be possible?

Again, how would other routers know this time if its only internally ?

I know this is too wild Smurf and is most probably wrong. But just to answer your question, I think other routers would not need to know the time stamp if it is only for the purpose of knowing the total time a packet stayed in the router and for decreasing the TTL of the packet when every second passes. Again, I don't think this is what is happening.

That doesn't sound right to me. How would router 2 know what time the packet left router 1? Unless I'm missing something about regular data packets having timestamps in them...

Hmm, what if the router timestamped the packets only internally? could that be possible?

Again, how would other routers know this time if its only internally ?

I know this is too wild Smurf and is most probably wrong. But just to answer your question, I think other routers would not need to know the time stamp if it is only for the purpose of knowing the total time a packet stayed in the router and for decreasing the TTL of the packet when every second passes. Again, I don't think this is what is happening.

100% right.


Just try out setting up a dumb network with 5 routers.
Send from end to end with a TTL of 4 and 5.

TTL within TCP/IP packages is the amount of hops.

TTL within DNS servers or DHCP servers is based on time.

On a second look, it appears that there is some thing called "TCP timestamps", en.wikipedia.org/wiki/Transmission_Contr...tocol#TCP_Timestamps

But it is used for a totally different purpose.

Hello guys, my first post to this board.

If you read this article www.informit.com/articles/article.aspx?p=680824&seqNum=4 i am sure you will get the answer.