In a proxy-chaining deployment, Yahoo IM10 users are unable to login, even though an unsupported IM user-agent policy is correctly installed on the child proxy.
An unsupported IM user-agent policy will ensure new IM clients are able to establish a connection through a single ProxySG (or single layer of ProxySGs), for example:
If however traffic from this first ProxySG (or layer of ProxySGs) is forwarded to a second ProxySG (or layer of ProxySGs) upstream, before going out to the internet, the ProxySG(s) in this second layer will need to be configured with http-handoff disabled for IM traffic.
This can be done either in the GUI as follows:
or in the CLI, like so:
#(config)im http-handoff disable