Q:

How to determine if ISP is blocking Ethereum traffic

My "Ethereum Wallet" from ethereum.org used to connect to several peers.  A while ago I noticed it was taking longer and longer to sync and the number of peers dropped.   It got worse, and seldom connected to more than 1 peer.  Now, it connects to none.

Is it possible that ISPs are blocking Ethereum traffic?
How can I determine if my ISP is blocking Ethereum traffic?
If ISPs do block the Ethereum network, how do we use Ethereum?

A:

It is possible an ISP is blocking traffic but unlikely.  In the UK they typically only block traffic under court order.
the following options could help you identify where the bottleneck is,

You can run the tracert command and use one of the ip addresses of a peer.
On windows it looks like this,
C:\>tracert 192.168.1.254

Tracing route to 192.168.1.254 over a maximum of 30 hops
---------------------------------------------------
1      2 ms       3 ms       2 ms      10.0.0.2
2     75 ms      83 ms      88 ms      10.0.0.1
3     73 ms      79 ms      93 ms      192.168.1.254

Trace complete.

This will at least show you the route between you and the peer that you could connect to is reachable, similar with
C:\Users\Admin\Desktop>tcping.exe 192.168.1.254 30303
C:\Users\Admin\Desktop>tcping.exe 192.168.1.254 30301 

with the tracert output you should be able to see any hops along the way that may be congested or dropping network packets.
if you can reach the peer and getting a response back then most likely the ISP is not blocking traffic.  If network packets are getting dropped along the route and your getting no response then it may indicate that something is blocking traffic.
It might be that only a specific type of traffic is being blocked such TCP/UDP on a specific port.

You can try using a VPN connection and connecting to a different country that does not block ethereum traffic.

