Packet loss

[vignesh7990]

Need help with a basic question

Below is the setup

Host1----SW1----R1-----R2----SW2----Host2

Questions:

1. There is intermittent connectivity between Host1 and Host2.

2. Traceroute from Host1 stops at R2. 

How do you troubleshoot?

Please let me know how to answer this. 

I was told interface speed and MTU were not considered valid answers. What could be the reasons for ping drops in this type of network assuming there are no routing or switching protocol issues.

[MHM Cisco World]

since half of ping failed then there is two path between the hosts, 
share the show ip route R1 and R2 

[vignesh7990]

I'm afraid this is all the information. The interviewer only wants to know the cause behind it assuming there is nothing wrong with the routing protocol configs or any STP issues. 

[MHM Cisco World]

as I inform you 50% meaning the packet is send through two path 
one path is OK 
other is not that why you get 50% success 

[Rich R]

1. There is intermittent connectivity between Host1 and Host2.
Does every second packet get lost or does it work for a few seconds then stop for a few seconds?

2. Traceroute from Host1 stops at R2. 
Does it always stop there or only when connectivity is lost?

Frankly I don't think there's enough information given here to give a proper answer.

[Joseph W. Doherty]

Like @Rich R too little information to begin to theorize actual cause, but you did ask about trouble shooting . . .

For starters, knowing more about what constitutes "intermittent connectivity".  For example, how often, how long, what time of day, what those two hosts were doing during breaks of connectivity, etc.

The traceroute stopping at R2 is interesting.  Can host1 ping host2?  If not, that, and with traceroute stopping at R2, might indicate an FW on host2 blocking traceroute and ping.  It might also block other traffic flows, which is why it's so important to get additional details on "intermittent connectivity".  Do the connectivity breaks appear in any way to be related to applications, and/or which host initiates the traffic between those two hosts, etc.?

Yet, there's so much more, about even just those two symptoms, the "intermittent connectivity" and stoppage of traceroute on R2, which might represent even two entirely different causes, or they could be from the same cause.

Again, besides obtaining as much information on the problem as possible, you can also do things like check the load and drop counts on all the transit interfaces, check for ACLs on R2 they might block traceroute, see if you can ping host2 from R2, etc.

It's possible, your interviewer possibly wasn't just looking for a particular "this is the cause", but how you might troubleshoot, your approach, what you're going to do and why, etc.

[MHM Cisco World]

He edit his post he remove 50% sucess ping which is keypoint here.

[Joseph W. Doherty]

"He edit his post he remove 50% sucess ping which is keypoint here."

Ah, I see that.  Indeed a very important point.

However, was the 50% exactly 50% or about 50%.  Was every other ping dropped, or groups of pings that totaled a 50% loss rate.

Diagram (including pre-edit) doesn't show an alternate path.

So, even with the 50% mention, not enough information to confirm your suggested cause, nor does it account for the traceroute stopping at R2.

But, as I wrote, there might be multiple underlying issues.  I.e. if every other ping is dropped, what you suggest as a cause would be a very strong contender for why the ping loss.