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Cisco Bug: CSCvi89197 - For 7000 & 8000 & NGIPSv, web interface allows interface MTU values lower than protocol minimum.

Last Modified

Dec 11, 2018

Products (1)

  • Cisco Firepower Management Center

Known Affected Releases


Description (partial)

On 7000 and 800 Series devices and NGIPSv, the web interface allows the user to set the MTU values for appliance interfaces, but the actual MTU value the system uses is 18 bytes less than the value the user enters. This means:
•	If the user enters an MTU value less than 1298, the MTU will not comply with the minimum IPv6 MTU setting of 1280.
•	If the user enters an MTU value less than 594, the MTU will not comply with the minimum IPv4 MTU setting of 576.

In addition, the web interface warns users of the incorrect minimum MTU values. For IPv6, the web interface warns users that the lowest supported value for IPv6 traffic is 1280—in truth, the lowest valid value the user should enter for IPv6 traffic is 1298. For IPv4, the web interface prevents users from entering a value lower than 576, while entering any value less than 594 results in an invalid IPv4 configuration.

Affects users configuring interfaces to use non-default MTU values.
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