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Per-Packet Load Balancing Does not Take Effect After Being Configured on an NE40.

Publication Date:  2013-01-08 Views:  36 Downloads:  0
Issue Description

Three MP-Groups are bundled together to the LPU of an NE40. After per-packet load balancing is configured on the LPU, only one of the MP-Group interface forwards traffic. There is no traffic on the other two MP-Groups.

Handling Process

After the problem occurs, SW_DEFINED_A value is: 0x10060000 is displayed on the LPU is slot 6. The value is 0.

All the three MP-Groups interfaces reside on the LPU in slot 6. The packets are sent to the inbound interface on the LPU in slot 6 in per-session load balancing mode. However, per-packet load balancing is configured on the outbound interfaces on the LPU, which causes the traffic forwarding to be unbalanced.

The Huawei R&D engineers check load balancing on the MP-Group interfaces on the NE40.

Based on the on-site Huawei technical support personnel's feedback, per-packet load balancing is configured on the outbound interfaces on the LPU in slot 6. However, per-session load balancing is used on the LPUs in other slots. The on-site Huawei technical support personnel change the load balancing mode to per-session mode on other LPUs. Information about load balancing on different LPUs is as follows.

[uzd_TASH-R1-diag]disp efu load-balancing 6

 Message sending success.

[uzd_TASH-R1-diag]

 SW_DEFINED_A value is: 0x10060000

 IP_balance_type = 1 

[uzd_TASH-R1-diag]

[uzd_TASH-R1-diag]

[uzd_TASH-R1-diag]disp efu load-balancing 4

 Message sending success.

[uzd_TASH-R1-diag]

 SW_DEFINED_A value is: 0x50000

 IP_balance_type = 0 

[uzd_TASH-R1-diag]

[uzd_TASH-R1-diag]

[uzd_TASH-R1-diag]disp efu load-balancing 5

 Message sending success.

[uzd_TASH-R1-diag]

 SW_DEFINED_A value is: 0x70000

 IP_balance_type = 0 

[uzd_TASH-R1-diag]

[uzd_TASH-R1-diag]

Root Cause

The configuration is not takes effect all LPU board.

Solution

Add load balancing configuration

Suggestions
The commands for configuring load balancing and their descriptions are as follows. load-balance flow all All LPUs perform per-session load balancing. load-balance packet all All LPUs perform per-packet load balancing. load-balance flow slot 2 The LPU in slot 2 performs per-session load balancing. load-balance packet slot 2 The LPU in slot 2 performs per-packet load balancing. In the hidden view: [en_]disp efu load-balancing (slot) displays the load balancing status of an LPU. You are advised to use the preceding command to check whether the flag is set to 1 after configuring load balancing. The command output helps check whether the load balancing configuration takes effect or not.

Principles:

The microcode has a global register SW_defined_A. Its structure is as follows.

flags_sw_defined_A   RECORD

   vpn_ttl_copy        : 1  ;

   MacLimit            : 1  ;Mac limit flag

   load_balance_type   : 2     ; Load balancing mode for IP packets

                                         ; 0: All the packets are forwarded in per-session load balancing mode.

                                         ; 1: All the packets are forwarded in per-packet load balancing mode.

                                         ; 2: The TCP packets are forwarded in per-packet load balancing mode, while the other packets are forwarded in per-session load balancing mode.

                                         ; 3: The UDP packets are forwarded in per-packet load balancing mode, while the other packets are forwarded in per-session load balancing mode.

   sw_reserved1             : 2

   atm_board_type           : 1            

   reserved2                : 1

   atm_ni_counter_disable   : 1 

   OC48_NS_Enable           : 1

   pos25_board_flag         : 1

   reserved3                : 5

   oqg_status               : 16

ENDS

The preceding structure of the microcode shows that the IP packets that come from the interface are sent to the NP. The NP extracts the IP addresses from the IP packets and searches the FIB table. Meanwhile, the NP checks whether the flag in SW_define_A is per-session. If per-packet load balancing is configured, the value of load_balance_type is 1, as displayed in.

In per-session load balancing mode, when packets enter an LPU, the LPU searches the FIB table and checks whether per-session or per-packet load balancing mode is used. If per-session load balancing is configured, the LPU extracts the source destination IP addresses from the packets for the hash algorithm. The hashed result is a fixed 16-bit number. Then the LPU searches the FIB table for the next hop based on the fixed 16-bit number. Since the packets of the same flow carry the same source and destination addresses, all the packets of the same flow are forwarded to the same next hop.

If there are only a few data flows, For example, eight of the ten flows may be forwarded through the same interface, or maybe no flows are transmitted through an interface.

Per-packet load balancing hashes a random number to select an outbound interface. Therefore, the outbound interface is not fixed. When traffic is heavy, the traffic can be evenly distributed between different outbound interfaces. Because searching the FIB table is performed on the inbound interface of the LPU, the outbound interface selection is also completed on the inbound interface of the LPU.

For example, a flow with the fixed source and destination IP addresses enters the LPU in slot 3 and leaves from the three outbound interfaces on the LPU in slot 4. In this case, although per-packet load balancing is configured on the LPU in slot 4, the mode does not take effect because the hashed result refers to only one outbound interface. As a result, all traffic is forwarded out through one of the outbound interfaces. However, after per-packet load balancing is configured on the LPU is slot 3, traffic can be load balanced on the LPU in slot 4.

END