ICP is broken in all the releases and master, but we have options for that: inter-colo peering to use the parent.config, local network peering to use the cluster.
refer to the official docutments for parent.config and cluster howto.
The ICP implementation in Traffic Server broke when epoll() was introduced. Its still an interesting and used feature in caches:
- when a caching layer of several boxes are used ICP helps to reduce disparities when a client is not routed to the same cache on subsequent requests
- after a restart, it can help reduce the time spent in a cold cache situation