How to define hostspec in grafana, using pcp vector

I am using PCP in distributed manner.
There are 4 hosts-

  1. Host1, Host2 : runs only pmcd
  2. Host3: runs only pmproxy
  3. Host4: running only Grafana server with pcp vector plugin.

I am using Grafana pcp-vector to connect to Host1 & Host2 pmcd via pmproxy running on Host3.

But I am not able to specify pmcd hostspec in grafana url.
Please suggest a procedure to define hostspec.