peer_connect_timeout

This is similar to connect_timeout, except that it applies to connections to your neighbors. Most likely, you'll want a smaller timeout for neighbor connections because they should be closer to you than most origin servers. If a neighbor is down, you want the connection to time out quickly so that you can try another source. Note that you can also specify individual neighbor timeouts with the connect-timeout option of the cache_peer directive.

peer_connect_timeout time-specification

peer_connect_timeout 30 seconds

peer_connect_timeout 15 seconds