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Enabling Fragmentation on GRE Tunnels

For GRE tunnel interfaces on Adaptive Services and MultiServices PICs only, you can enable fragmentation of IPv4 packets in GRE tunnels.

By default, IPv4 traffic transmitted over GRE tunnels is not fragmented. To enable fragmentation of IPv4 packets in GRE tunnels, include the clear-dont-fragment-bit statement:




clear-dont-fragment-bit;

You can include this statement at the following hierarchy levels:

[edit interfaces interface-name unit logical-unit-number]
[edit logical-systems logical-system-name interfaces interface-name unit logical-unit-number]

When you include the clear-dont-fragment-bit statement in the configuration, the don’t-fragment (DF) bit is cleared on all packets, even packets that do not exceed the tunnel maximum transmission unit (MTU). If the packet’s size exceeds the tunnel’s MTU value, the packet is fragmented before encapsulation. If the packet’s size does not exceed the tunnel’s MTU value, the packet is not fragmented.

You can also clear the DF bit in packets transmitted over IP Security (IPSec) tunnels. For more information, see Enabling IPSec Packet Fragmentation.

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