Merge pull request #47438 from fasigpt/master

Update documentation on AMQP Port Requirements

Author: ktoliver

articles/service-bus-messaging/media/service-bus-amqp-protocol-guide/amqp4.png

@@ -78,6 +78,15 @@ Azure Service Bus currently uses exactly one session for each connection. The Se
 
 Connections, channels, and sessions are ephemeral. If the underlying connection collapses, connections, TLS tunnel, SASL authorization context, and sessions must be reestablished.
 
+### AMQP outbound port requirements
+
+Clients that use AMQP connections over TCP require ports 5671 and 5672 to be opened in the local firewall. Along with these ports, it might be necessary to open additional ports if the [EnableLinkRedirect](https://docs.microsoft.com/dotnet/api/microsoft.servicebus.messaging.amqp.amqptransportsettings.enablelinkredirect?view=azure-dotnet) feature is enabled. `EnableLinkRedirect` is a new messaging feature that helps skip one-hop while receiving messages, thus helping to boost throughput. The client would start communicating directly with the back-end service over port range 104XX as shown in the following image. 
+
+![List of destination ports][4]
+
+A .NET client would fail with a SocketException ("An attempt was made to access a socket in a way forbidden by its access permissions") if these ports are blocked by the firewall. The feature can be disabled by setting `EnableAmqpLinkRedirect=false` in the connectiong string, which forces the clients to communicate with the remote service over port 5671.
+
+
 ### Links
 
 AMQP transfers messages over links. A link is a communication path created over a session that enables transferring messages in one direction; the transfer status negotiation is over the link and bi-directional between the connected parties.