python recvfrom not working when on different ip

Ok so i am a newbie into networking.
I wrote a python script to be a client and another python script to be a server. I used UDP sockets inside both and used sento and recvfrom to post and receive. No when i have both the client and server on the same system using localhost as the host, messages are transferred with ease. Now when I put the server script on a actual server, it does not receive. I put the host ids on both the scripts as the IP of the server. I tried tcpdump and found out that messages are actually sent to the destination port and netstat confirms that the port is listening. Now here is a little twist the server has 3 interfaces.. eth1 , eth0 and lo. I dont know how to specify what to aim at but i know tcpdump shows that eth0 is the one thats getting messages. I tried with the IP's of both interfaces and still doesn't work. I cant understand how can a port listen and get messages but still not show it.

here is the code:
//Server

import socket,struct,IN
# Set the socket parameters
host = "10.73.***.**"
port = 45333
buf = 1029
addr = (host,port)

# Create socket and bind to address
UDPSock = socket.socket(socket.AF_INET,socket.SOCK_DGRAM)


UDPSock.bind(addr)

# Receive messages
while 1:
data,addr = UDPSock.recvfrom(buf)
if not data:
print "Client has exited!"
else:
print "\nReceived message '", data,"'"

# Close socket
UDPSock.close()

************************************************** ***
//client
import socket

MCAST_GRP = '10.73.***.**'
MCAST_PORT = 45333

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
#sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, 2)
while 1:
sock.sendto("robot", (MCAST_GRP, MCAST_PORT))


************************************************** ********

SOMEBODY PLEASE HELP.

Another update here. I tried the same client server code on another network and it worked just like the way it should. But it just doesnt work in one network. I just can't guess what could be the problem. Is it some configuration in the network??