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Report for Package loss because of the asymmetry HASH when S9300 send L2/L3 layer multicast stream together

Publication Date:  2012-09-19 Views:  133 Downloads:  0

Issue Description

In this test environment, we have two HUAWEI S9300 switches, and they connect each other by Eth-trunk link;
The version of the software in switches is S9300V100R006C00SPC500;
HX-1 and HX-2 configure that send L2/L3 layer stream together; the configuration in detail is in the file attachment.

Tport_1 send Stream_1: the destination IP is;
Tport_2 send Stream_2: the destination IP is;
HX-2 is DR;
When we bidirectional send multicast line rate stream, found out the package loss rate is around 50%.

Alarm Information


Handling Process

2/3 layer multicast copy mechanism
1. Send stream from vlanif11 at DR, the BDR will receive the IGMP request of vlanif10 and won’t handle this message, so this message will transmit to DR by the 2 layer vlan10. DR create the outbound interface when it received the IGMP request; so the stream from vlanif11 at DR will copy to vlanif10 by the 3 layer, and arrive at the BDR by the interface of Eth-trunk.
2. The Eth-trunk link between DR and BDR join in the vlan10 and vlan11, and both vlanif10 and vlanif11 run PIM protocol, they will send PIM Hello to each other; when the 2 layer multicast receives the Query or PIM Hello, they will create the router port; so the Eth-trunk interfaces at vlan10 and vlan11 are router ports.
3. When send L2/L3 layer stream together, the outbound interface is the PC port and the router port in the 2 layer multicast. So the stream of vlanif11 at DR will copy to vlan11 by 2 layer, and send to BDR by the Eth-trunk interface.
4. At this moment, the Eth-trunk interface have the multicast stream at vlan 10 and vlan 11, and this multicast stream have the same source IP address and destination IP address.
Illuminate of the asymmetry HASH of Eth-trunk interface in this test
From the theory description above, we can know that the Eth-trunk interface is in physical link layer (2 layer protocal), it can do the HASH calculation according to the source MAC/IP address or destination MAC/IP address of the frame, or share the load to different physical link by enhance  template.
The current verison of S9300 can configure the unknown-unicast load-balance, configure the enhance  template, it can do the HASH calculation by VLAN.
When the multicast message check the chip entry to do the 2/3 layer multicast copy in the test, the inbound stream has only one multicast stream, the outbound stream have two multicast streams with the same source and destination IP addresses.
1. We can’t configure the HASH load share by the configuration of the load share of Eth-Trunk interface, so the multicast stream is transmitted by the IP address, and isn’t controlled by the HASH indicate in the physical link.
2. We can’t configure the HASH load share by the configuration of the unknown-unicast load-balance, so now is multicast message, it won’t hit the HIT indicate.

In the version current, the HASH calculation is actualized by the chip multicast message, it can’t actualized by the commands that the two multicast streams with the same source IP address and destination IP address have the symmetry HASH at the Eth-trunk link.

Root Cause

In this test topology, when Tport_2 send Stream_2, DR will copy the stream by 3 layer multicast and transmit to Vlanif10, at the same time, DR will copy the stream by 2 layer multicast in Vlan11. So now Eth-Trunk bearer two share of stream.
When we send the link rate stream at the inbound interface, the package loss rate reach to 50% because the asymmetry HASH of the Eth-trunk link.


From the analysis above, the failure cause in this test is the unidirectional multicast stream which is bigger than 500M. this stream copied by the 2/3 layer multicast, produced a steam with the bandwidth more than 1G, so result in the pacakage loss in the physical link; so we can ameliorate in this test as below:
1. Take the 10GE optical fiber  port as the physical link of S9300, in this case, even if send a line rate multicast stream  from the inbound port , this stream can produce a flux more than 2G after the 2/3 layer multicast copy, the 10 GE link won’t loss the package
2. Or change the  bidirectional send multicast line rate stream to bidirectional send 2 share 500M multicast stream, and adjust the multicast addresses, separate the 4G stream copied by the 2/3 layer multicast to 4 links of the Eth-trunk. In this case, the package won’t loss. In reel, one port often send multi-mulitcast stream, so we suggest take this way in the test. If must be the one port send 1G stream bidiretional, we suggest take the advise 1 above.
3. Change the configuration and the topology, don’t do the 2/3 layer multicast copy in the equipment. Now the line rate multicast stream won’t loss the package in the 1G physical link of Eth-Trunk. But this way related to the redundancy rotate performance, we can achieve the no package loss after we sacrifice the redundancy rotate performance and the reliability.