I was able to solve this.
is a sample configuration
In my case the Apache server and eduCommons were physically different also I did not had a Local DNS entry for internal server where eduCommons was present.
So on the front end Apache I needed to have in /etc/hosts
a line which tells
is mapped to which IP on LAN internally.So that when you forward a request HTTP_HOST it does not start querying
DNS on internet.
The correct format on Server A is
Where HTTP_HOST is what the client on internet requested.
I did not had a local DNS entry to point HTTP_HOST to my URL_B where eduCommons is.
So in /etc/hosts
URL_B should be mapped to HTTP_HOST.
Then URL_B in proxy pass directive should not have IP address.
You can use HTTP_HOST also provided you mapped HTTP_HOST with URL_B_Where_eduCommons_is .
Do not include the port number to map.
Some links which helped