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Outgoing Traffic of the ME60 Is Unbalanced Because the Number of Next Hops Is Not an Nth Power of 2

Publication Date:  2012-07-27 Views:  46 Downloads:  0
Issue Description

 Networking:
The ME60 running V100R005C02B01B sp12 is connected to the egress CR1 through two GE interfaces (1 and 2) and connected to the egress CR2 through three GE interfaces (3, 4, and 5). Traffic is evenly sent through the five GE interfaces. To expand the capacity, the customer creates two GE interfaces (6 and 7) on the ME60 to connect CR1 and two GE interfaces (8 and 9) to connect CR2.
Fault description:
After the four GE links are added, traffic is unevenly transmitted on the nine GE links. That is, traffic is evenly transmitted over links 3 to 9 but traffic transmitted over each of link 1 and link 2 is only a half volume of traffic over any of link 3 to 9. 

 

Alarm Information

 Routing information:
(In the displayed information, digits replace the IP addresses of interfaces.)
<ME60>
Destination/Mask Proto Pre Cost Flags NextHop Interface
0.0.0.0/0 O_ASE 150 6 D 3 GigabitEthernet2/0/0
O_ASE 150 6 D 4 GigabitEthernet2/0/1
O_ASE 150 6 D 5 GigabitEthernet2/0/2
O_ASE 150 6 D 8 GigabitEthernet2/0/3
O_ASE 150 6 D 9 GigabitEthernet2/0/4
O_ASE 150 6 D 1 GigabitEthernet1/0/0
O_ASE 150 6 D 2 GigabitEthernet1/0/1
O_ASE 150 6 D 6 GigabitEthernet1/0/3
O_ASE 150 6 D 7 GigabitEthernet1/0/4
Interface traffic:
<ME60>disp interface G1/0/0
Last 5 minutes output rate: 92751704 bits/sec, 28709 Packets/sec
<ME60>disp interface G1/0/1
Last 5 minutes output rate: 95529224 bits/sec, 28202 Packets/sec
<ME60>disp interface G1/0/3
Last 5 minutes output rate: 206752608 bits/sec, 60175 Packets/sec
<ME60>disp interface G1/0/4
Last 5 minutes output rate: 198448256 bits/sec, 58340 Packets/sec
You can find that the volume of traffic sent on G 1/0/0 and G 1/0/1 is a half of that on G 1/0/3 and G 1/0/4. 

 

Handling Process

 Do as follows:
1. Check routing entries and forwarding entries on the ME60. No abnormalities are found.
2. Check NHP entries with the nine GE links being the default next hops of routes.
[ME60-diag]efu np2800 slot 1 ingress display A076C7C0 //A076C7C0 is the displayed memory address. The address varies with the software version. Running this command is risky and it is recommended to use this command under the direct supervision of Huawei R&D personnel.
a076c7c0: 0000 0302 xxxx 1909 0000 0080 0000 0000
a076c7d0: 0000 0104 xxxx 1905 0000 0080 0000 0000
a076c7e0: 0000 0103 xxxx 1901 0000 0080 0000 0000
a076c7f0: 0000 0300 yyyy e586 0000 0080 0000 0000
a076c800: 0000 0301 yyyy e58a 0000 0080 0000 0000
a076c810: 0000 0303 xxxx 190d 0000 0080 0000 0000
a076c820: 0000 0304 xxxx 1911 0000 0080 0000 0000
a076c830: 0000 0100 yyyy e57e 0000 0080 0000 0000 //Corresponding to G 1/0/0
a076c840: 0000 0101 yyyy e582 0000 0080 0000 0000 //Corresponding to G 1/0/1
a076c850: 0000 0302 xxxx 1909 0000 0080 0000 0000
a076c860: 0000 0104 xxxx 1905 0000 0080 0000 0000
a076c870: 0000 0103 xxxx 1901 0000 0080 0000 0000
a076c880: 0000 0300 yyyy e586 0000 0080 0000 0000
a076c890: 0000 0301 yyyy e58a 0000 0080 0000 0000
a076c8a0: 0000 0303 xxxx 190d 0000 0080 0000 0000
a076c8b0: 0000 0304 xxxx 1911 0000 0080 0000 0000
In the preceding information, the first two digits in 0101 and 0101 indicate slot 1 and the last two digits indicate interfaces 0 and 1. The first two digits in 0304 indicate slot 2 (the ME60-8 is a half-chassis device, and thus both 02 and 03 indicate slot 2) and the last two digits indicate interface 4. yyyy e57e is the hexadecimal IP address of the next hop interface corresponding to G 1/0/0.
3. The preceding information shows only the next hops corresponding to G 1/0/0 and G 1/0/1 appear once, and each of the next hops corresponding to the rest seven GE interfaces appears twice. This is consistent with the fact.
4. Disable one of the new GE interfaces (for example, interface 9). In this case, the ME60 is connected to each of CR1 and CR2 through four GE links. That is, the ME60 has eight next hops, and thus traffic is balanced among the eight GE interfaces. 

 

Root Cause
 Possible causes are as follows:
1. It is preliminarily considered that V100R005 supports only eight equal-cost routes, and thus the problem occurs. However, nine routing entries and nine forwarding entries of the ME60 are found. In addition, the version specification shows that the ME60 supports load balancing among 16 equal-cost routes.
2. Load unbalance is caused by the hash algorithm. In this version, the lower-order 4 bits of the hash results of the source and destination IP addresses are selected, and thus 16 results are obtained. The 16 results can be evenly distributed only when the number of next hops is less than 16 and is the nth power of 2. 

 
 
Suggestions
 Suggestion:
When adding equal-cost links to an ME60, you are recommended to set the total number of links to the nth power of 2. 

 
 

END