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Cannot browse the Internet through the GRE tunnel, but able to ping and Telnet

Core Issue

This issue is most likely caused by fragmentation of packets needed to pass traffic, but the Don't Fragment (DF) bit is set.


Increase the Maximum Transmission Unit (MTU) to 1524 or use Policy-Based Routing (PBR) to clear and set the DF bit. Another option is to change the Transmission Control Protocol (TCP) Maximum Segment Size (MSS) option value on Synchronization (SYN) packets that traverse through the router.

For more information, refer to Why Can't I Browse the Internet when Using a GRE Tunnel?.


Multiple devices on different network


Multiple devices

Source and Destination Physical Connectivity

Source and destination exist on different subnetwork

Connected over tunnel interface

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Last update:
‎06-22-2009 04:36 PM
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