A host is fragmenting packets regardless of the DF setting in IP packet headers, which may affect network performance.
- Avoid deploying VPN solutions that ignore DF flags in the IP header.
- If detected on a router, ensure router microcode has been upgraded to the latest version.
- In Windows operating systems along the test path, review the MTU registry keys in "HKEY_LOCAL_MACHINE \ SYSTEM \ CurrentControlSet \ Services \ Tcpip". Either delete the MTU key, or change its value to reflect the MTU of all NIC cards installed (typically 1500 byte MTU defined by 1518 byte frame size). Note that on Windows operating systems the MTU registry key is created and set by some versions of Cisco VPN installation programs, and uninstalling does not remove the key. </ul>
- "Path MTU may be incorrectly discovered"
Related topics"Black-hole hop detected - MTU conflicts possible"
Other resourcesRFC 791 RFC 792 RFC 1191