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FAQ: What Are Differences Between Fast ICMP Reply and Non-fast ICMP Reply on the ME60?

Publication Date:  2013-09-03 Views:  38 Downloads:  0
Issue Description
What are differences between fast ICMP reply and non-fast ICMP reply on the ME60?
Handling Process
N/A
Root Cause
N/A
Solution
1. Process of the fast ICMP reply:
Version: ME60 V100R006
ME60 client----ME60 transfer---ME60 server
The preceding shows a typical fast ICMP reply scenario. The ping client connects to the ping server through one or more ping transfers that perform IP forwarding. The preceding roles process ICMP Echo Request messages as follows:
1.1 Ping client
The process of sending an ICMP Echo Request message is as follows:
a. The user invokes the ping program and provides required parameters.
b. The ping program constructs the header of an ICMP Echo Request messages based on the parameters, creates a raw socket, and transmits data to the IP layer.
c. The IP layer creates an IP header, determines the next hop and outbound interface based on FIB table, determines whether fragmentation is required, and transparently transmits data to the interface card through the virtual path (VP). (The preceding operations are complete on the main control board.)
d. The interface card invokes the sending function at the data link layer for adapting the message format and sends the message as a byte stream.
The process of receiving an ICMP Echo Reply message is as follows:
a. After receiving the data, the interface card analyzes the data link layer header and puts the message in the inbound IP queue.
b. The interface card obtains the IP message and analyzes the header based on the FIB table. After finding that the destination address is the local address, the interface card analyzes the transportation layer protocol. Upon finding ICMP Echo Reply, the interface card sends the message to the main control board.
c. The raw socket process accepts the message and puts it in the receiving buffer.
d. The ping program reads data from the receiving buffer. After verifying that the data is correct and does not time out, the ping program displays a message "Reply from..."
1.2 Ping transfer
a. After receiving the data, the interface card analyzes the data link layer header and puts the message in the inbound IP queue.
b. An interface card obtains the IP message and analyzes the header. If an option header exists, the interface card transparently transmits the message to the main control board through the VP. If the outbound port of the message is on the local card, the interface card invokes the sending function on the data link layer to send the message to the main control board; if the outbound port of the message is not on the local card, the interface card transparently transmits the message to the interface card where the outbound port is located through the VP. If no option header exists, the interface card searches the FIB table for the outbound interface.
1.3 Ping server
a. After receiving the data, the interface card analyzes the data link layer header and puts the message in the inbound IP queue.
b. The interface card obtains the IP message and analyzes the header based on the FIB table. After finding that the destination address is the local address, the interface card analyzes the transportation layer protocol. Upon finding ICMP Echo Request, the interface card processes the message. If the message is fragmented or carries an option header, the interface card sends the message to the main control board.
c. When the ICMP Echo Request message is not sent to the main control board, the interface card sends an ICMP Echo Reply message from the inbound interface after swapping the source and destination IP addresses and changing the ICMP protocol number. The fast ICMP reply message is delivered through the default BE queue.
2. Comparison between methods of processing the fast ICMP reply and non-fast ICMP reply messages on the ME60:
On the ping client and ping transfer, a non-fast ICMP Echo Reply message is processed in the same way as that of processing a fast ICMP Echo Reply message. However, on the ping server, after an ICMP Echo Request is sent to the main control board, the CPU constructs an ICMP Echo Reply message and delivers it to the interface card. The message is delivered through the CS6 queue. When the CPU of the ping server is busy processing a large number of services, the ping server sends ICMP Echo Reply messages with a long delay. After fast ICMP reply function is configured, ICMP Echo Request messages are not sent to the main control board for processing, reducing the reply time.

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