3Com 10014299 Number discarded, Set Tunnel Interface to Check with Checksum, Gre key key-number

640 CHAPTER 44: CONFIGURING GRE

Set the identification key word of tunnel	gre key key-number
interface.
Cancel the identification key word of	undo gre key
tunnel interface.

By default, no identification key word of the tunnel interface is configured.

Setting the Tunnel It is stipulated in RFC 1701 that if the checksum field of the GRE header is set, the Interface to Check with checksum is valid. The transmitting side calculates the checksums of GRE header Checksum and payload. The receiving side calculates the checksum of the received message and compares it with the checksum field in the message. If the two checksums are

identical, the message will be processed, otherwise it will be discarded.

If only one end of the tunnel is configured to check with the checksum, the message will not be checked with checksum. Only when both ends of the tunnel are configured to check the checksum, the message will be checked with the checksum.

Perform the following tasks in the tunnel interface view.

Table 692 Set Tunnel Interface to Check with Checksum

Operation	Command
Set tunnel interface to check with check	gre checksum
sum.
Disable tunnel interface to check with	undo gre	checksum
check sum.

By default, the tunnel interface to check with the field of checksum is disabled.

Settng the Tunnel It is stipulated in RFC 1701 that if the sequence-datagram in the GRE header is set, Interface to Synchronize both the receiving side and the transmitting side will synchronize the sequence the Datagram Sequence numbers. The synchronized message should be further processed, or it is

Number discarded.

With the sequence numbers, the message is unreliable but in order. The receiving end establishes sequence numbers for the message, which is received by the local end and successfully de-encapsulated. The sequence numbers are integers between 0 and 232–1 and the sequence number of the first packet is 0. After the channel is established, the sequence numbers is accumulated and cyclically counted. If the receiving end receives a message whose sequence number is less than or equal to that of the message received the last time, the packet will be considered illegal. If the receiving end receives an out-of-order message, the packet will be discarded automatically.

Only when the synchronization mechanism to enable or disable sequence numbers is established at both ends of the tunnel, the channel can be established.

Perform the following tasks in the tunnel interface view.

Table 693 Set the Tunnel to Synchronize Datagram Sequence Numbers

Operation	Command
Set tunnel interface to synchronize	gre sequence-datagrams
sequence numbers.