Discover IPv6 Path MTU(PMTU) with PMTU Discovery Tool (With Video and KB Article)

Discover IPv6 Path MTU(PMTU) with PMTU Discovery Tool (With Video and KB Article)

Firmware/Software Version: 5.9 and above.


Video Tutorial:  Click here for the video tutorial of this topic

Feature/Application:

Every network link has a maximum packet size (MTU). The full transmission path (between the source node and the destination node) may cross different link MTUs and the smallest link MTU on the path is path MTU (PMTU). For IPv6 packets,  when the source node attempts to transmit a packet to a destination node through a router that has a link MTU smaller than the packet size, th IPv6 router will automatically send an ICMPv6 Packet Too Big message back to the source node.  When the source node receives the message, it will adjust the outgoing packet size to the updated PMTU value.

PMTU Discovery Tool supports IPv6 PMTU discovery from SonicOS 5.9. PMTU Discovery Tool is a diagnostic tool which can determine the maximum transmission unit (MTU) on the network path between the SonicWall security appliance and a remote host.  It aims to assisting operators in troubleshooting MTU related network problems. Operator can determine the MTU size on a network path and configuring the MTU for the SonicWall security appliance below the path MTU size, to avoid the potential delay caused by negotiation of the MTU size and other MTU related network issues.

Note: For IPv4 PMTU discovery, you can refer to the following article.

UTM - Determining the MTU Value for Your Internet Connection using PMTU Discovery option in Diagnostics page of GUI.

Procedure:

Step 1: Navigate to System > Diagnostics page


Step 2:  Under Diagnostic Tools, in the Diagnostic Tool drop down list choose "PMTU Discovery".


Step 3: In the Path MTU Discovery to this host or IP address field, enter the destination IPv6 address and press button  "GO" to measure the PMTU. PMTU will be displayed in the popup window.