From:	IN%"Mark.Jacobson@uni.edu"  "MARK JACOBSON" 30-MAR-2000 18:28:05.21
To:	IN%"810-023-01@uni.edu"
CC:	
Subj:	ping -i and TTL and routers....

Hi 023 students,

    Notice the output below here of  tracert www.uiowa.edu 
    command and then of the          ping -i 4 www.uiowa.edu command.

    Router with IP number 205.221.255.10 informed the pinger user
    that the TTL expired in transit.

    If each router subtracts 1 from the TTL, we have
                            starbase1 subtracting 1 from 4 giving 3
                            uni-gate  subtracting 1 from 3 giving 2
                            207.165.237.137       1 from 2 giving 1
                            UIA-ICN-t3            1 from 1 giving 0

        and the ping request TTL reached 0, so the packet is thrown away
        by the UIA-ICN-t3 router because its Time To Live expired.
                                             -    -  -

C:\>tracert www.uiowa.edu

Tracing route to www.uiowa.edu [128.255.56.81]
over a maximum of 30 hops:

  1    10 ms   <10 ms   <10 ms  starbase1.uninet.uni.edu [134.161.128.1]
  2   <10 ms   <10 ms   <10 ms  uni-gate.uni.edu [134.161.1.101]
  3   <10 ms    50 ms   100 ms  207.165.237.137
  4    20 ms    10 ms    10 ms  UIA-ICN-t3.icn.state.ia.us [205.221.255.10]
  5     *        *       10 ms  cisco-lc.uiowa.edu [128.255.3.2]
  6    10 ms    10 ms    10 ms  lime.weeg.uiowa.edu [128.255.56.81]

Trace complete.

C:\>ping -i 4 www.uiowa.edu

Pinging www.uiowa.edu [128.255.56.81] with 32 bytes of data:

Reply from 205.221.255.10: TTL expired in transit.
Reply from 205.221.255.10: TTL expired in transit.
Reply from 205.221.255.10: TTL expired in transit.
Reply from 205.221.255.10: TTL expired in transit.

     This has been a review of the 3/30 hands-on Wright 112 lab class,
          which did not last until 3:30 p.m. after all.

     Mark