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User Manual - Configuration Guide (Volume 3)
Versatile Routing Platform
Chapter 3
Configuration of GRE
3-6
compares it with the check sum in the message. If the two check sums are identical, the
message will be further processed, or it will be discarded.
If only one end of the tunnel is configured to check with the check sum, the message
will not be checked with check sum. Only when both ends of the tunnel are configured
to check with the check sum, can the message be checked with the check sum.
Perform the following task in tunnel interface configuration mode.
Table VPN-3-7 Set tunnel interface to check with check sum
Operation Command
Set tunnel interface to check with check sum. tunnel checksum
Disable tunnel interface to check with check sum. no tunnel checksum
Disable tunnel interface to check with check sum by default.
3.2.9 Setting Tunnel Interface to Synchronize Datagram Serial Number
It is stipulated in RFC 1701 that: if “sequence-datagram” in GRE header is set, both
receiving side and transmitting side will synchronize serial numbers. The synchronized
message should be further processed, or it is discarded.
With the serial numbers, the message is unreliable but in order. The receiving end
establishes serial numbers for the message which is received by local end and
successfully de-encapsulated (The serial numbers are integers between 0 and 2
32
–1
and the serial number of the first packet is 0). After the channel is established, the serial
numbers will be accumulated and cyclically counted. If the receiving end receives a
message whose serial number is less than or equal to that of the message received last
time, the packet will be considered as illegal. If the receiving end receives an orderless
message, the packet will be automatically discarded.
Only when the synchronization mechanism to set/disable serial numbers is established
at both ends of the tunnel, can the channel be established.
Perform the following task in tunnel interface configuration mode.
Table VPN-3-8 Set the tunnel to synchronize datagram serial numbers
Operation Command
Set tunnel interface to synchronize serial numbers. tunnel sequence-datagrams
Disable tunnel interface to synchronize serial numbers. no tunnel sequence-datagrams
Disable tunnel interface to synchronize datagram serial numbers by default.
3.3 Monitoring and Maintenance of GRE
Perform the following task in privileged user mode.
Table VPN-3-9 Monitoring and maintenance of GRE
Operation Command
Show the working status of tunnel interface. show interface tunnel [tunnel-number]