Gre Checksum - 3Com 3C13618 Command Reference Manual

3Com Router Command Reference Guide — V1.00
The above information shows: Tunnel 1 interface is in up state, and MTU is 128 bytes.
The network address of Tunnel1 is 3.1.1.1; 0 packet is received; 0 error packet and 0
broadcast packet is received; no packet is discarded; 0 packet is sent; 0 packet is
output with errors, 0 broadcast packet and 0 packet with unknown protocol is output.

2.1.3 gre checksum

Syntax
gre checksum
undo gre checksum
View
Tunnel interface view
Parameter
None
Description
Using the gre checksum command, you can configure checksum-based end-to-end
check at both ends of the tunnel. Using the undo gre checksum command, you can
disable the checksum check on the tunnel interfaces.
By default, checksum check is disabled on tunnel interface.
RFC 1701 provides that: if the Checksum bit is set in the GRE packet header, then
Checksum is valid. The sender calculates the checksum based on the GRE header
and payload, and the receiver calculates the checksum based on the received packet
and compares it with the checksum contained in the packet. If they are the same, the
packet will be further processed, otherwise it will be discarded.
If the checksum is set at one end of the tunnel only, then no checksum-based check
will be performed on the packet. Only when the checksum is set at both ends of a
tunnel, will the packet be checked.
For related commands, see interface tunnel.
Example
# Set up a tunnel between RouterA and RouterB, whose tunnel interfaces are tunnel0
and tunnel1 respectively. It is required to enable the checksum check.
[RouterA-Tunnel0] gre checksum
[RouterB-Tunnel1] gre checksum
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