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Cisco Bug: CSCvt73619 - Tunnel path-mtu-discovery does not copy DF bit

Last Modified

Oct 19, 2020

Products (1)

  • Cisco Catalyst 9500H Series Switches

Known Affected Releases

16.12.2 16.12.3 16.9.3

Description (partial)

GRE tunnel with "tunnel path-mtu-discovery" configured.

When data packet is coming with df-bit set, GRE headend device is not copying the DF bit from the data IPv4 header to the GRE IPv4 header.

For self-generated packets, with df-bit set - df-bit is set both on IPv4 and GRE header. As a result, correct MTU is discovered.

Found on C9500H running 16.9.3, 16.12.02 and 16.12.03
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