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ZTE AC broadcasts untag Arp packets and causes the interconnection failure with S9312

Publication Date:  2012-10-25 Views:  2 Downloads:  0
Issue Description
Please see the networking pic at attachment. 

The gateway of ZTE-AP locates at ZTE-AC .ZTE-AC-1 is the master AC.ZTE-AC-2 is the standby AC. Huawei S9312 interconnects ZTE-AP and ZTE-AC. S9312 transmits VLAN 512 from ZTE-AP to ZTE-AC transparently. The interface XG2/0/1 is at 12*10GE board of S9312.
In S9312-A,when the interface linking with ZTE-AC and the interface linking with another S9312 locate at the same board, if the ZTE master and standby AC switchover,the service is normal.Otherwise,when the two interfaces locate at different boards, the packets will be lost when master and standby AC switchover.
Alarm Information
NULL
Handling Process
Step1:Using the laptop to capture the packets at the uplink port of AP and the downlink port of AC. The Arp broadcast packets can be captured.
Step 2:Examine the mac address table at S9312-A and S9312-B when ZTE-AC switchover,we find that in S9312-A, the mac address of AC can be learnt by XG2/0/1 instead of XG1/0/11.It is confusing.
Step 3: When ZTE-AC switchover,login on XG2/0/1 of S9312-B,summing all the packets belong to VLAN 512,the result is zero.
Step 4. When ZTE-AC switchover,login on XG2/0/1 of S9312-B,summing all the packets, the untag arp broadcast packets appear.Because the XG2/0/1 is set as trunk mode,at this time,the port will discard the untag arp broadcast packets from standby AC. Moreover, in S9312,the 12*10G board which is used to linked with ZTE-AC is class “A” board. For version V1R3,the class “A” board refreshes the mac address table based on the “flow”.Because the arp request packets have been discarded by S9312-B, the 2# board of S9312-A cannot receive the arp packets and refresh the mac address table formed before ZTE-AC switchover.Before ZTE-AC switchover,the 2# board of S9312-A can learn the mac address of ZTE-AC.It explains the question of step 2: why in S9312-A, the mac address of AC can be learnt from XG2/0/1 instead of XG1/0/11.Thus,the trouble lies in the ZTE-AC.However, because the laptop can capture packets regardless of vlan tag,at step1,we can get the arp broadcast packets.
Step 5:When ZTE-AC swithover,the ZTE-AP also broadcast arp request packets to get the ZTE-AC mac address.The S9312-A and S9312-B transmit the packets transparently to ZTE standby AC.The ZTE standby AC will reply the request. The reply are unicast packets and arrive at S9312-A’s XG1/0/11 instead of XG2/0/1.In another word,the 2# board cannot receive arp packets to refresh the mac address table. In this case,the G6/0/44 of S9312-A sometimes learn the mac address from the XG1/0/11 , sometimes from XG2/0/1.
Step 6:In conclusion,after ZTE-AC switchover(i)the untag arp request packets from AC to AP are discarded by S9312-B (ii) the arp reply from AC to AP are unicast packets so that they cannot be received by 2#board of S9312-A.In these two cases,the 2#board of S9312-A cannot receive information to refresh the mac address table.It explains the symptom referred above: In S9312-A,when the interface linking with ZTE-AC and the interface linking with another S9312 locate at the same board, if the ZTE master and standby AC switchover,the service is normal.Because the board can receive the arp reply to refresh the mac address table.
Step 7:At V1R3,there is a command to enable global mac learning to resolve this trouble:
[S9303_223.67]global-mac-learning enable slot ?
INTEGER<1-3,5> Existing slot number
After this step, the service is normal.
Root Cause
1. Capture the packets and locate the exact place where the packets are lost
2. Find out the data forwarding method when trouble happens by means of analyzing mac address table.
3. Find out the reason for packets loss via traffic flow statistics
Suggestions
Summary:For class “A” board,different version has different mac address refreshment mechanism.V1R1 and V1R2 are software global refreshment mechanism while V1R3 are based on “flow”.A command is provided to enable global mac learning.

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