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# What information does pathping give you?

Posted on 2011-10-13
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How can routers closer have higher RTT than routers farther away?

This Node/Link tells how much loss for packets sent to the router ip address and the loss between the router and the next router? Which direction?

Source to Here tells how much loss between my computer running pathping and that router?

D:\>pathping -n corp1

Tracing route to corp1 [10.54.1.196]
over a maximum of 30 hops:
0  172.16.87.35
1  172.16.87.218
2  192.168.52.1
3  192.168.80.1
4  10.54.247.14
5  10.54.1.196

Computing statistics for 125 seconds...
Hop  RTT      Lost/Sent = Pct                     Lost/Sent = Pct  Address
0                                                                                   172.16.87.35
0/ 100 =  0%   |
1   41ms     0/ 100 =  0%                       0/ 100 =  0%  172.16.87.218
13/ 100 = 13%   |
2   22ms    16/ 100 = 16%                     3/ 100 =  3%  192.168.52.1
0/ 100 =  0%   |
3   24ms    13/ 100 = 13%                     0/ 100 =  0%  192.168.80.1
0/ 100 =  0%   |
4   21ms    14/ 100 = 14%                     1/ 100 =  1%  10.54.247.14
0/ 100 =  0%   |
5   24ms    13/ 100 = 13%                      0/ 100 =  0%  10.54.1.196

Trace complete.

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Question by:Dragon0x40

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TheCleaner earned 1400 total points
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How can routers closer have higher RTT than routers farther away?

- The RTT is between the router and the next one.  So for hop #2 it is the RTT between 172.16.87.218 and 192.168.52.1 (not between 172.16.87.35 and 192.168.52.1).

This Node/Link tells how much loss for packets sent to the router ip address and the loss between the router and the next router? Which direction?

- Yes, the loss between the router and the next router, the direction is "forwarded" (forward) meaning from the "first" router in the hop to the 2nd.

Source to Here tells how much loss between my computer running pathping and that router?

- no, it is a column header (everything makes more sense in a bigger command prompt window).  It is from the source of that HOP to "here" being the address on the far right column.  So for hop #4 it is from 192.168.80.1 (source) to 10.54.247.14 (here)
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That's where he got his "example"...at least part of his data is from that link.  He changed his external IPs to match the article.

My guess was that he read the article and was still needing clarification...
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Author Comment

ID: 36963747
Still need some more clarification. RTT and loss over link designated by the pipe sign | seem to be measuring the speed and loss of the links between router 1 and 2, 2 and 3 etc.

I still don't understand two other calculations. I put a <-- beside what I am unsure about.

Hop  RTT      Lost/Sent = Pct                                               Lost/Sent = Pct  Address
0                                                                                                        172.16.87.35     <--- comp running pathping
0/ 100 =  0%   |
1   41ms     0/ 100 =  0%                                              0/ 100 =  0%  172.16.87.218
13/ 100 = 13%   |           <--- pkt loss over link 87.218 to 52.1
2   22ms    16/ 100 = 16%                                           3/ 100 =  3%  192.168.52.1
0/ 100 =  0%   |
3   24ms    13/ 100 = 13%                                          0/ 100 =  0%  192.168.80.1    <- pkt loss 87.35 dest for 80.1
0/ 100 =  0%   |
4   21ms    14/ 100 = 14%<-loss 247.14 to  87.35      1/ 100 =  1%  10.54.247.14
0/ 100 =  0%   |
5   24ms    13/ 100 = 13%                                            0/ 100 =  0%  10.54.1.196

Trace complete.

I did read some information on pathping before submitting this question but I did not understand everything.

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TheCleaner earned 1400 total points
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I typed it wrong on my explanation about "source to here", when I listed the IPs, so that might be confusing you.  It should have read:

- no, it is a column header (everything makes more sense in a bigger command prompt window).  It is from the source of that HOP to "here" being the address on the far right column.  So for hop #4 it is from 172.16.87.35 (source) to 10.54.247.14 (here)

<----comp running pathping = just that...the computer you ran pathping on

<----pkt loss over link 87.218 = by default pathping does 100 queries to each router in the path.  So here 13 of those queries failed, which means it is experiencing a 13% loss between 87.218 and 52.1

<--- pkt loss 87.35 dest for 80.1 = same as above.  Here however it experience 0% forwarding loss...meaning the packets sent between 80.1 and 247.14 (you have to think of it from the column headers.  So "This Node/Link" corresponds to the address on the right most column.  Then use a sentence if you must, so line/hop 3 would read as:

"Hop #3 had a RTT of 24ms.  The source of 172.16.87.35 sent 100 queries and lost 13 to the router 192.168.80.1.  Router 192.168.80.1 sent 100 queries and lost 0 queries.  The queries were sent to the next Node/link listed in the next hop...hop #4."

<----loss 247.14 to 87.35 = close...but the other way around.  The source 87.35 sent 100 queries to 247.14 and lost 14 of those.

The "source to here" column will always show the queries sent from SOURCE to ROUTER address in that hop (far right column).  Thus if there is a problem on hop #2 there will almost always be a problem in this same column in the remaining hops.

The "this node/link" column will always show the queries sent from ROUTER address (far right column) TO the ROUTER address in the next hop.

Does that help?
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Author Comment

ID: 36965881
You explained it very well! Thank you.

I have one question and I can open another question for it.

How does my computer running path ping. Determine RTT and packet loss from one router to the next?

For example the router in hop 2 doesn't physically send a ping to the router in hop 3?

All the pings come from my computer running the pathping correct?
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TheCleaner earned 1400 total points
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Yes, all ICMP packets are coming from your computer.  Technically it is sending ICMP echos to each router listed in each hop.  The "router to router" stats are based on a calculation between each hops results.

For your instance, if hop #1 has 13% source to here loss, and hop #2 has 16% source to here loss, it is assumed that the additional 3% came because of loss between the routers involved in hop 1 and 2.

Hop #3 has 13% source to here loss, so it is assumed that since the loss is the same as the "source to here" loss in hop #1 that there wasn't any additional loss between the routers...the loss for hop #3 was due to the same "loss cause" as hop #1...

Does that make sense?
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giltjr earned 600 total points
ID: 36969870
A router that is close to you could have a higher RTT because its CPU is busier and it needs to process the ping request in software.

In your example the router with IP address 172.16.87.218  has to respond to the ping request.  Its CPU could be busy for some reason and so it takes longer to process the request and respond.

Now, the other routers may not be as busy, so they can respond faster.  The router 172.16.87.218 does not need to "process" the pings to the other routers, it just needs to relay them using hardware (typically).  So even though its CPU may be busy, it is just passing the packets in hardware and so CPU busy does not come into play.
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