Merge pull request #291717 from papadeltasierra/pauldsmith/twamp

Explain TWAMP, UDP, NATs.

Author: v-dirichards

articles/operator-nexus/TOC.yml

@@ -332,6 +332,8 @@
           href: troubleshoot-lacp-bonding.md
         - name: Troubleshoot NAKS Cluster Node Packet Loss
           href: troubleshoot-packet-loss.md
+        - name: Troubleshoot TWAMP (UDP) not working
+          href: troubleshoot-twamp-udp-not-working.md
     - name: Tenant Workload
       expanded: false
       items:

articles/operator-nexus/troubleshoot-twamp-udp-not-working.md

@@ -0,0 +1,37 @@
+---
+title: "Azure Operator Nexus: TWAMP (UDP) not working"
+description: Learn how to troubleshoot TWAMP (UDP) issues.
+author: papadeltasierra
+ms.author: pauldsmith
+ms.service: azure-operator-nexus
+ms.custom: azure-operator-nexus
+ms.topic: troubleshooting
+ms.date: 12/10/2024
+# ms.custom: template-include
+---
+
+# Troubleshoot TWAMP (UDP) not working
+
+TWAMP (Two-Way Active Measurement Protocol) over UDP (User Datagram Protocol) doesn't work if NAT (Network Address Translation) occurs between the Session-Sender and the Session-Reflector and/or Control-Client and Server. Typically the Session-Sender and Control-Client reside in one network and the Session-Reflector and Server reside in a second network. 
+
+Examples where NAT can occur include any meeting between two LANs (Local Area Networks) with independent addressing such as a connection to/from a VLAN (Virtual LAN).
+
+TWAMP over TCP (Transmission Control Protocol) can work through a NAT providing the Session-Reflector and Server have IP addresses outside the address range of the subnet in which the Session-Sender and Control-Client reside. The IP addresses of the Session-Reflector and Server IP addresses must also be unique along the entire path.
+
+## Diagnosis
+
+TWAMP (UDP) is configured but doesn't work. Network traffic analysis shows traffic leaving the Control-Client and/or Session-Sender but not returning from the Server and/or Session-Reflector.
+
+## Mitigation steps
+
+No mitigation is possible. Two-way UDP protocols can't traverse networks where address translation occurs without extra logic elements such as an ALG (Application-level Gateway).
+
+Two-Way TCP protocols can traverse a NAT providing that the TCP connection is established from inside the NAT to outside. This traversal is possible because a long-lived connection is established through the NAT and traffic in the return direction flows along this connection. UDP traffic doesn't establish a long-lived connection so there's no defined path back through the NAT for return traffic to follow.
+
+
+
+## Related content
+
+- The TWAMP protocol is described in [A Two-Way Active Measurement Protocol (TWAMP)](https://datatracker.ietf.org/doc/html/rfc5357).
+- If you still have questions, contact [Azure support](https://portal.azure.com/?#blade/Microsoft_Azure_Support/HelpAndSupportBlade).
+- For more information about support plans, see [Azure support plans](https://azure.microsoft.com/support/plans/response/).