On GRE tunnel interfaces only, you can enable reassembly of fragmented tunnel packets. To activate this capability, include the reassemble-packets statement:
-
reassemble-packets;
You can configure this statement at the following hierarchy levels:
For each tunnel you configure on the interface, you can enable or disable fragmentation of GRE packets by including the allow-fragmentation or do-not-fragment statement:
-
allow-fragmentation;
-
do-not-fragment;
You can configure these statements at the following hierarchy levels:
If you configure allow-fragmentation on a tunnel, it clears the DF bit in the outer IP header, enabling post fragmentation of GRE-encapsulated packets if the packet size exceeds the maximum transmission unit (MTU) value for the egress interface. By default, packets that exceed the MTU size are dropped and post fragmentation of GRE packets is disabled.
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Note: Whenever you configure allow-fragmentation on a tunnel, you must also include either the tunnel key or the clear-dont-fragment-bit statement. This configuration enables the router to send affected packets to the PIC so that the correct IP header can be placed in the fragments. Otherwise, on the reassembly side some packets might be lost when fragments arrive in the PIC out of sequence at high speeds. |
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