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Cisco IP Phone can't register after LLDP is enabled in S5700LI

Publication Date:  2014-05-06 Views:  127 Downloads:  0
Issue Description
customer added Huawei Switch S5700LI to the current network where all the devices are Cisco devices, and some Cisco IP Phone 7911G are connected to S5700LI. For management, LLDP in S5700LI is enabled, but after that, the IP Phone can’t register. If LLDP is disabled, the IP phone can register.
Alarm Information
none
Handling Process
Step1: Two IP Phones in the same model are connected to the same Switch, one IP Phone can register while the other can’t register
Two IP Phones 7911G are connected to S5700LI, and when LLDP is enabled globally, the IP Phone connecting to GE0/0/1 can’t register while the other IP Phone connecting to GE0/0/3 can register normally.
The two IP Phones interact with S5700LI via LLDP packet, and LLDP neighbor can established normally:
[BM-TEST-S5700]display lldp neighbor brief
Local Intf   Neighbor Dev             Neighbor Intf             Exptime
GE0/0/1      SEP0024C443D150      0024C443D150:P1           144   
GE0/0/3      SEP0024C443465C.cisco... 0024C443465C:P1           136

Step2: Open the debug information in S5700LI by the command “debug lldp packet”, and capture the LLDP interacting packet between the two IP Phones and 5700LI
(1) From the packet, we can see there is no difference for LLD packet sending by the two IP Phones
The packet sent by the IP Phone to the interface GE0/0/1 of S5700LI:



The packet sent by the IP Phone to the interface GE0/0/3 of S5700LI



(2) From the packets, we can see there is no difference for LLD packet sending by S5700LI to the two IP Phones
The packet sent by the Switch to IP Phone connected to interface GE0/0/1



The packet sent by the Switch to IP Phone connected to interface GE0/0/3



Comparing the packets, it is found that there is no difference in the LLDP packets between the two IP Phones and S5700LI, and S5700LI can handle the LLDP packets sent by the two IP Phones normally.
Step3:  Connect a PC to S5700LI and configure the same network segment as the IP Phone connected to GE0/0/1, then PC ping IP Phone failed.
When IP Phone is connected to Switch, it will interact with the device whose IP address is 10.10.10.18 to get some files:



Then it will interact with the device whose IP is 10.10.100.11in TCP, finish the register via the protocol Cisco-sccp:



From the above, it can be seen that to finish the register, the IP Phone and the devices whose IP are 10.10.10.18,10.10.100.11 need be reachable.
To test interaction between IP Phone and other device, connect a PC to S5700LI and configure the same network segment as the IP Phone connected to GE0/0/1, and ping from PC to IP Phone. The IP address for IP Phone is 172.21.154.13, and for PC is 172.21.154.200.
The ping result is failed. Captured the packet, and it’s found that PC didn’t received ARP Reply from IP Phone, which due to PC can’t learn the corresponding ARP and resulted in the Ping failure.



From the above packet, it can be seen that IP Phone didn’t reply ARP Reply packet normally, which result in that the IP Phone can’t interact register packet with upper device.
Step4:  Try to configure this command in S5700LI GE0/0/1interface”undo lldp tlv-enable med-tlv network-policy”, and IP Phone can register successfully.
After the configuration, the LLDP packet sent by S5700LI no longer includes Network policy TLV, then the IP Phone connected to GE0/0/1 can register normally。
The LLDP neighbor between S5700LI and IP Phone can still be established normally:
<BM-TEST-S5700>dis lldp neighbor  brief
Local Intf   Neighbor Dev             Neighbor Intf             Exptime
GE0/0/1      SEP0024C443D150.cisco... 0024C443D150:P1           157   
GE0/0/3      SEP0024C443465C.cisco... 0024C443465C:P1           149   
----End
Root Cause
The same model IP Phones handle LLDP packet in different ways, even if the interfaces in Switch S5700LI that IP Phones connected have the same configuration.
The IP Phone that can’t register normally can’t handle LLDP sent by S5700LI normally, and this IP Phone doesn’t send ARP Reply packet, which causes IP Phone can’t interact with upper devices.
Suggestions
For the usage of QoS for voice, Network Policy TLV includes L2 priority, DSCP value and other information. In order to resolve this issue from the root, it is recommended to check the  configuration for different model of IP Phone to find out which configuration in IP Phone causes the IP Phone handle LLDP packet in different way.

END