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[Troubleshooting Series] Case 52 ICMP Rate Limit does not Take Effect

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Physical Network Topology

As shown in the figure, two CE12800s are directly connected, and ICMP speed limit is configured on SwitchB. The command is as follows: icmp rate-limit interface 10GE 2/0/1 threshold 1

Figure 1-1 ICMP rate limit



Fault Description

When SwitchA pings SwitchB, the ICMP speed limit function does not take effect on SwitchB. The detailed information is as follows:

[CE12800_A] ping
  PING 56  data bytes, press CTRL_C to break
    Reply from bytes=56 Sequence=1 ttl=254 time=1 ms
    Reply from bytes=56 Sequence=2 ttl=254 time=1 ms
    Reply from bytes=56 Sequence=3 ttl=254 time=1 ms
    Reply from bytes=56 Sequence=4 ttl=254 time=1 ms
    Reply from bytes=56 Sequence=5 ttl=254 time=1 ms
  --- ping statistics ---
    5 packet(s) transmitted
    5 packet(s) received
    0.00% packet loss
    round-trip min/avg/max = 1/1/1 ms

Normally, there should be ICMP loss-limited packet loss.

Configuration Files

l   Confguration on SwitchA

interface Vlanif1111
 ip address
interface 10GE1/0/1
 port link-type trunk
 port trunk allow-pass vlan 5 10 to 30 300 1111 3000
 stp disable
 device transceiver 10GBASE-COPPER

l   Configuration on SwitchB

user-interface con 0
user-interface vty 0 4
 authentication-mode none
 user privilege level 3
 idle-timeout 0 0
 protocol inbound telnet

1.1.2 Troubleshooting Location

Troubleshooting Procedure

                               Step 1      Check that SwitchB receives the ICMP packet normally and finds that the packet has been sent from the chip to the CPU.

<CE12800_B> display cpu-defend statistics packet-type icmp slot 1/4  
Statistics(packets) on slot 1/4 :
PacketType               Total Passed        Total Dropped   Last Dropping Time
                    Last 5 Min Passed   Last 5 Min Dropped
icmp                                5                    0   -
                                    5                    0

                               Step 2      Check whether the CPU receives ICMP packets and speed limit on the CPU.

<CE12800_B> debugging ip icmp

                               Step 3      After ICMP debugging is enabled, it is found that no ICMP is sent to the CPU to check whether the interface board fast returns ICMP packets.

<CE12800_B> display icmp fast-reply statistics slot 1/4 
------------------------ Display ICMP Statistics -------------------------------
Received packets:                                                               
     request packets:                             5                             
     invalid request packets:                     0                             
     failed to get vrf:                           0                             
     destination is not host ip:                  0                             
     failed to get ctrl word:                     0                             
Send packets:                                                                    
     successful reply packets:                    5                             
     failed reply packets:                        0                             

The display shows that ICMP packets are processed back by the interface and are not sent to the CPU of the main control board.

                               Step 4      Turn off the ICMP echo-reply fast function.

[CE12800_B] icmp echo-reply fast disable

                               Step 5      Verify on SwitchA as follows.

<CE12800_A> ping                                         
  PING 56  data bytes, press CTRL_C to break
    Reply from bytes=56 Sequence=1 ttl=255 time=15 ms
    Request time out
    Reply from bytes=56 Sequence=3 ttl=255 time=2 ms
    Request time out
    Reply from bytes=56 Sequence=5 ttl=255 time=1 ms
  --- ping statistics ---
    5 packet(s) transmitted
    3 packet(s) received
    40.00% packet loss
round-trip min/avg/max = 1/6/15 ms

It has been verified that the ICMP speed limit function takes effect.


Root Cause

The ICMP rate limit function is in conflict with the default ICMP rate limit function. The rate limit function does not take effect.


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