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#3321 - 11/09/18 01:22 AM PingPlotter not showing first hop
Graham Wideman Offline


Registered: 11/09/18
Posts: 3
I have used PingPlotter for years, generally very happily. But today I hit a puzzle I've not seen before.

From a LAN behind a router, when tracing to a site on the internet, the first hop is always, so far as I can remember, the router/gateway. So on subnet 192.168.100.0/24, the first hop is generally 192.168.100.1.

But today, on a LAN that is behind router A, which in turn is downstream from an LTE modem/router B, PingPlotter skips the router A gateway address, and shows router B's gateway address as the first hop.

So where the LAN subnet is 192.168.100.0/24, and the link between router A and LTE modem is 192.168.0.xx, PingPlotter shows the first hop as 192.168.0.1.

PingPlotter is happy to show pings from 192.168.100.1 if you enter that destination specifically (and, no surprise, just one hop is shown). But if you enter 192.168.0.1 as the destination, then you still get only one hop, to 192.168.0.1.

For what it's worth, the PC running PingPlotter has address 192.168.100.30, and shows a gateway address of 192.168.100.1.

I have tried this with latest version PingPlotter, and also v3.5.something. Same result.

Any ideas on why this happens? Thanks.

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#3322 - 11/09/18 01:36 PM Re: PingPlotter not showing first hop [Re: Graham Wideman]
Hayla Offline

Pingman Staff


Registered: 10/16/17
Posts: 46
Hey there!

Thanks for getting in touch.

If you issue a command line traceroute, what do you see? PingPlotter goes off of traceroute - so it should be showing you the same thing as command line. Let us know!
_________________________
Regards,
Hayla

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#3324 - 11/09/18 10:25 PM Re: PingPlotter not showing first hop [Re: Hayla]
Graham Wideman Offline


Registered: 11/09/18
Posts: 3
Originally Posted By: Hayla

If you issue a command line traceroute, what do you see? PingPlotter goes off of traceroute - so it should be showing you the same thing as command line. Let us know!


Thanks for replying.

tracert 8.8.8.8 (for example) shows the same anomaly -- it skips the first hop to the gateway.

Code:

-----------------------------------------------------
C:\Users\RDP1User>tracert 8.8.8.8

Tracing route to google-public-dns-a.google.com [8.8.8.8]
over a maximum of 30 hops:

  1    <1 ms    <1 ms    <1 ms  192.168.0.1
  2    37 ms    30 ms    33 ms  172.26.96.161
  3    49 ms    36 ms    38 ms  107.72.231.228
  4     *        *        *     Request timed out.
  5    71 ms    36 ms    28 ms  12.83.179.49
  6    29 ms    27 ms    35 ms  12.122.104.117
  7    52 ms    36 ms    35 ms  12.255.10.162
  8     *        *        *     Request timed out.
  9    34 ms    54 ms    30 ms  74.125.251.38
 10    34 ms    36 ms    34 ms  108.177.3.235
 11    45 ms    34 ms    33 ms  google-public-dns-a.google.com [8.8.8.8]

Trace complete.

C:\Users\RDP1User>tracert 192.168.100.1

Tracing route to 192.168.100.1 over a maximum of 30 hops

  1    <1 ms    <1 ms    <1 ms  192.168.100.1
------------------------------------------------------

And here's the route table of the PC on which I'm running PingPlotter:

IPv4 Route Table
===========================================================================
Active Routes:
Network Destination        Netmask          Gateway       Interface  Metric
          0.0.0.0          0.0.0.0    192.168.100.1   192.168.100.30    281
        127.0.0.0        255.0.0.0         On-link         127.0.0.1    331
        127.0.0.1  255.255.255.255         On-link         127.0.0.1    331
  127.255.255.255  255.255.255.255         On-link         127.0.0.1    331
    192.168.100.0    255.255.255.0         On-link    192.168.100.30    281
   192.168.100.30  255.255.255.255         On-link    192.168.100.30    281
  192.168.100.255  255.255.255.255         On-link    192.168.100.30    281
        224.0.0.0        240.0.0.0         On-link         127.0.0.1    331
        224.0.0.0        240.0.0.0         On-link    192.168.100.30    281
  255.255.255.255  255.255.255.255         On-link         127.0.0.1    331
  255.255.255.255  255.255.255.255         On-link    192.168.100.30    281
===========================================================================

As you can see, traffic has to pass through the gateway at 192.168.100.1.

So, not a problem with PingPlotter per se. But a puzzle discovered while using PingPlotter.

Anyhow, this seems to be a question that arises not infrequently, as
google traceroute skips gateway first hop
shows. Looks like it's to do with router configuration, and apparently the router not decrementing the ping packet TTL counter. So I guess I'll research it along that path.

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