[All About Switches] A Switch Fails to Connect to a Cisco Device Through an Eth-Trunk Interface in LACP Mode

Latest reply: Mar 9, 2018 00:39:24 1539 1 0 0

Involved Products and Versions

All products and versions

Networking

As shown in Figure 1-1, SwitchA and SwitchB set up a cluster and are connected to a Cisco device through a transmission device SDH. In addition, SwitchA and SwitchB are bound to Eth-Trunk10. The link between the interfaces GE2/2/0/47 and FE0/45 is operated by China Mobile, while the link between the interfaces GE1/2/0/47 and FE0/46 is operated by China Telecom.

Figure 1-1 Networking diagram for the failure to connect a switch to a Cisco device through an Eth-Trunk interface

20180308112516716001.png

 

Fault Symptom

After an Eth-Trunk is configured, the link operated by China Telecom becomes abnormal, and the member interface GE1/2/0/47 of Eth-Trunk10 is in unselect state. If no Eth-Trunk is configured and the link operated by China Mobile is cut off, the test result of the link between the interfaces GE1/2/0/47 and FE0/46 shows that SwitchB can communicate with the Cisco device properly.

Cause Analysis

1.       Check the configuration on SwitchA.

#
interface Eth-Trunk10
 port link-type trunk
 port trunk allow-pass vlan 2 to 4094
 stp config-digest-snoop  
 mode lacp
#
interface GigabitEthernet2/2/0/47
 description link to SDH
 eth-trunk 10

Check the configuration on SwitchB.

#
interface Eth-Trunk10
 port link-type trunk
 port trunk allow-pass vlan 2 to 4094
 stp config-digest-snoop  
 mode lacp
#
interface GigabitEthernet1/2/0/47
 description link to SDH
 eth-trunk 10

Check the configuration on the Cisco device.

interface FastEthernet0/45
 switchport trunk encapsulation dotlq
 switchport mode trunk
 ip arp inspection trust
 speed 100
 duplex full
 no cdp enable
 channel-group 10 mode active
 ip dhcp snooping trust
interface FastEthernet0/46
 switchport trunk encapsulation dotlq
 switchport mode trunk
 ip arp inspection trust
 speed 100
 duplex full
 no cdp enable
 channel-group 10 mode active
 ip dhcp snooping trust

2.       After the preceding configurations are checked, it is found that the fault is not related to the configurations.

The duplex mode of the interfaces on the SDH is half-duplex, and the speed 100 command is run to configure the interfaces to work at 100 Mbit/s. However, Huawei switches work in auto-negotiation mode and the interface rate is 1000 Mbit/s. Therefore, the switch interfaces work at 100 Mbit/s in half-duplex mode after negotiation. The SDH, however, discards LACP packets in half-duplex mode.

Troubleshooting Procedure

                          Step 1     Change the negotiation mode of SwitchA and SwitchB to non-auto-negotiation.

----End

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gululu
Admin Created Mar 9, 2018 00:39:24 Helpful(0) Helpful(0)

thanks for your sharing!
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Come on!

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