how can I communicate between instances of openstack

I have created few instances on openstack,is it possible to communicate between them using ip addresses directly using ssh or any configuration steps are required

Solution

Depends. If installation of Openstack components, bridges, configurations are correct pinging between VMs is a simple thing to do. If not check the following:

Make sure VMs got IP addresses
If VMs are not getting IP, check DORA packets are observed going out of compute node and received at network node. On network node check for DHCP namespace of the VM's network.
In security group rules allow icmp and ssh.
Identify the compute node and respective switches to which these VMs are attached to.
Do iptables -L and make sure icmp/ssh traffic is not blocked.

This is not a comprehensive checklist but should give some idea why traffic is failing.