I have limited experience, so am looking to be pointed in the right direction.
I have a server and a client that are 90mi away (by car). Both are on comcast home internet with similar speeds. I started diagnosing with iperf3, I found that the connection was only 2Mbps on average between the client and server, much lower than all other servers and other clients with the same server I tried. I then ran a ping and testroute (on the client) which revealed that the last hop to the server was over 1sec in latency. This is likely the cause of the bandwidth restriction but Im not sure what to do now. I have full access to both points, how do I fix the route between them?
Were you able to get a name resolved for the problem node? If not, increase the timeout for each reply until you get one. When I was trying to determine the ping spikes I was getting while gaming, I had to set a timeout of over 20 minutes before I could get name resolution on the problem node. I was then able to determine the problem node was a backbone provider and there was nothing I could do, cause the ISP was holding them hostage.
Once you get a name resolved, you can determine if you’re a customer of theirs. If so, you can contact them and complain. If you’re not, you’re out of luck. Nothing you can do. That’s just the nature of networks.
If Im understanding you correctly, there was no timeout, the connection works but has a latency of about 1000ms. All the connections in the traceroute are comcast servers.
I think you might be right about the congestion. I was seeing the latency last night but traceroute just now is 20ms. Except iperf3 still shows the same bandwidth restriction, so Im not sure what to make of it, besides that the traceroute is actually unrelated to the original problem.
I just realized I never really stated the original issue clearly, which is the poor connection, restricted bandwidth according to iperf3. I can see it with real world testing by trying to stream video hosted on the server to the client and playback is interrupted with frequent buffering. Suppose I need to do more troubleshooting, any favorite tools?
You can’t fix the route between them (as you don’t own the network) unless you change one or both ISPs as the network node/link involved is not yours to manage.
If Comcast own the network, all you can do is complain to Comcast, but good luck with that.
edit:
when you say last hop - is that YOUR remote router (i.e., your remote network’s gateway), or Comcast’s?
If it’s YOUR router on the other end, then it may be too slow for the connection (CPU wise) and need an upgrade. if it’s an old router, it may not have been built to handle the traffic it is currently attempting to process. Alternatively it is under DOS.
If you have administrative control of the remote router, my first diagnostic would be to monitor the CPU on it.