Port Channel load balancing issue

[EleazarFuen]

I have an inquiry about a configuration I deploy in a C2960 switch. I have configured a ether channel with 8 ports, the load balanced method is source mac address. The bundling protocol is LACP.

I have found the ether channel is not balanced as I expect. One of the eight interfaces is congested.

*Detail of   congestion interface:

… GigabitEthernet1/0/2   is up, line protocol is up (connected) …       reliability 255/255, txload 238/255, rxload 32/255    ***congested interface*** …

I been reviewing some documents about the configuration of the ether channel and configuration looks and behave as is expected. Port channel all interfaces are active:

switch#sh   int po1 Port-channel1   is up, line protocol is up (connected)     Hardware is EtherChannel, address is ...........     Description: INSIDE-MASTER   MTU   1500 bytes, BW 8000000 Kbit, DLY 10 usec,        reliability 255/255, txload 34/255, rxload 33/255     Encapsulation ARPA, loopback not set     Keepalive set (10 sec)     Full-duplex, 1000Mb/s, link type is auto, media type is unknown     input flow-control is off, output flow-control is unsupported   Members   in this channel: Gi1/0/1 Gi1/0/2 Gi2/0/1 Gi2/0/2 Gi3/0/1 Gi3/0/2 Gi4/0/1 Gi4/0/2    ***eight interfaces***   ARP   type: ARPA, ARP Timeout 04:00:00   Last   input never, output 00:00:00, output hang never   Last   clearing of "show interface" counters 20w0d     Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops:   1662386899   ***Drops for congested interface GigabitEthernet1/0/2*** …

…     Queueing strategy: fifo     Output queue: 0/40 (size/max)   30   second input rate 1053373000 bits/sec, 165017 packets/sec   30   second output rate 1082746000 bits/sec, 173079 packets/sec        755178023967 packets input, 628737602889253 bytes, 0 no buffer        Received 3681164 broadcasts (3234870 multicasts)        0 runts, 0 giants, 0 throttles        0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored        0 watchdog, 3234870 multicast, 0 pause input        0 input packets with dribble condition detected        852162422509 packets output, 699901291834183 bytes, 0 underruns        0 output errors, 0 collisions, 0 interface resets        0 babbles, 0 late collision, 0 deferred        0 lost carrier, 0 no carrier, 0 PAUSE output        0 output buffer failures, 0 output buffers swapped out …

Here is the LACP information

switch#sh   lacp 1 internal Flags:  S   - Device is requesting Slow LACPDUs           F - Device is requesting Fast LACPDUs           A - Device is in Active mode       P - Device   is in Passive mode Channel group   1                               LACP port     Admin       Oper    Port        Port Port        Flags   State       Priority        Key       Key       Number      State Gi1/0/1     SA      bndl        32768           0x1       0x1       0x102       0x3D Gi1/0/2     SA      bndl        32768           0x1       0x1       0x103       0x3D Gi2/0/1     SA      bndl        32768           0x1       0x1       0x202       0x3D Gi2/0/2     SA      bndl        32768           0x1       0x1       0x203       0x3D Gi3/0/1     SA      bndl        32768           0x1       0x1       0x302       0x3D Gi3/0/2     SA      bndl        32768         0x1         0x1       0x303       0x3D Gi4/0/1     SA      bndl        32768           0x1       0x1       0x402       0x3D Gi4/0/2     SA      bndl        32768           0x1       0x1       0x403       0x3D

switch#sh   lacp 1 neighbor Flags:  S   - Device is requesting Slow LACPDUs           F - Device is requesting Fast LACPDUs           A - Device is in Active mode       P - Device   is in Passive mode Channel group   1 neighbors Partner's   information:                     LACP   port                          Admin  Oper   Port    Port Port        Flags   Priority  Dev   ID            Age    key    Key      Number  State Gi1/0/1     SA      255         0009.0fe7.5aed  23s    0x0      0x11   0x1     0x3D Gi1/0/2     SA      255         0009.0fe7.5aed  22s    0x0      0x11   0x2     0x3D Gi2/0/1     SA      255         0009.0fe7.5aed  22s    0x0      0x11   0x3     0x3D Gi2/0/2     SA      255         0009.0fe7.5aed  21s    0x0      0x11   0x4     0x3D Gi3/0/1     SA      255         0009.0fe7.5aed  23s    0x0      0x11   0x5     0x3D Gi3/0/2     SA      255         0009.0fe7.5aed  19s    0x0      0x11   0x6     0x3D Gi4/0/1     SA      255       0009.0fe7.5aed     7s    0x0    0x11     0x7     0x3D Gi4/0/2     SA      255         0009.0fe7.5aed  30s    0x0      0x11   0x8     0x3D

The only difference I’ve found against the cisco documentation is that when the etherchannel was configured the interfaces where added in UP state.

Since I suspect this would affect the etherchannel hash calculation, I would like to know is if I shutdown the etherchannel (all interfaces goes down) and then “no shutdown” over the etherchannel , it would calculate again the etherchannel hash and redistribute the traffic over the other ports.

I appreciate any help,

Best Regards

[blau grana]

Hello Eleazar,

I do not know if shut/no shut will make difference. I think that either nothing change or some other interface will become congested.

You should change load balancing method because src-mac method is probably not diversing traffic equally.

http://www.cisco.com/en/US/docs/switches/lan/catalyst2960/software/release/12.2_55_se/configuration/guide/swethchl.html#wp1276203

Best Regards

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[Steven Clinton]

You should look at what traffic is most diverse, is the source mac the most different or is the destination Mac? Maybe it's the destination ip or source ip.

Look at the direction that the majority of your traffic flows to and then find what the biggest distinguished is of that traffic.

Or if you don't want to go through the work, you can just change the load balancing method until you get the desired results

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