LACP load balancing traffic Question

[Fotiosmark]

Hello guys,

I have 2 3750 stacked core switches, which are connected through Port Channels to another Switch SG550x.
The port channels are Up and running with LACP.

Now my question is if Load Balancing between the link is working correctly. Basically I noticed the below output and made me wonder.

SW-ATH-FL-1-1#sh int po7 counters etherchannel

Port            InOctets   InUcastPkts   InMcastPkts   InBcastPkts
Po7            370113685        919769         23900          3191
Gi1/0/7        214116829        377278          9892          2827
Gi2/0/7        155996856        542491         14008           364

Port           OutOctets  OutUcastPkts  OutMcastPkts  OutBcastPkts
Po7           7120967776       5025912         13777          1291
Gi1/0/7       7107957507       4935311         11068           588
Gi2/0/7         13010269         90601          2709           703
SW-ATH-FL-1-1#
SW-ATH-FL-1-1#
SW-ATH-FL-1-1#sh int po10 counters etherchannel

Port            InOctets   InUcastPkts   InMcastPkts   InBcastPkts
Po10                8756             0            65             0
Gi1/0/10            4314             0            32             0
Gi2/0/10            4442             0            33             0

Port           OutOctets  OutUcastPkts  OutMcastPkts  OutBcastPkts
Po10             1495268           926          7070          4706
Gi1/0/10         1020769           701          5824          3307
Gi2/0/10          474499           225          1246          1399

As you can see Po7 has allot more traffic that Po10, as Po10 especially the incoming, are 0.

Load Balance Option was that to begin with.

EtherChannel Load-Balancing Configuration:
        src-mac

EtherChannel Load-Balancing Addresses Used Per-Protocol:
Non-IP: Source MAC address
  IPv4: Source MAC address

Now from the SG side, similar situation

SG-ATH-FL-1-2#sh interfaces counters Port-Channel10

      Port       InUcastPkts  InMcastPkts  InBcastPkts    InOctets   
---------------- ------------ ------------ ------------ ------------
      Po10          789032      7781378      5114787     1723609550  

      Port       OutUcastPkts OutMcastPkts OutBcastPkts  OutOctets   
---------------- ------------ ------------ ------------ ------------
      Po10            0          67688          0         9191966    

FCS Errors: 0
Single Collision Frames: 0
Multiple Collision Frames: 0
SQE Test Errors: 0
Deferred Transmissions: 0
Late Collisions: 0
Excessive Collisions: 0
Carrier Sense Errors: 0
Oversize Packets: 0
Internal MAC Rx Errors: 0
Symbol Errors: 0
Received Pause Frames: 0
Transmitted Pause Frames: 0
SG-ATH-FL-1-2#sh interfaces counters Port-Channel7

      Port       InUcastPkts  InMcastPkts  InBcastPkts    InOctets   
---------------- ------------ ------------ ------------ ------------
      Po7         966319538     13301411     1656422    465234381899
                                                        4            

      Port       OutUcastPkts OutMcastPkts OutBcastPkts  OutOctets   
---------------- ------------ ------------ ------------ ------------
      Po7         457086099     20950049     3458883    119415057565
                                                        38          

Anybody has any good idea on where I should be searching for the reasons on that behavior?

[Fotiosmark]

also I have noticed this also.

SW-ATH-FL-1-1#test etherchannel load-balance interface po7 mac 0023.5eab.e3c1 0015.6242.2025
Would select Gi1/0/7 of Po7

SW-ATH-FL-1-1#test etherchannel load-balance interface po10 mac 0023.5eab.e3c1 0015.6242.2025
Would select Gi1/0/10 of Po10

The mac address is the Local SVI of Vlan, and the destination is on a local interface on 2 different routers. Both Po7 and 10 are connected on the same Stacked Switch.

So basically 2 Core Stack, and to Distr. Stack, with 2 Port channels.

Is there a way to make it go to both interface?

Would select Gi1/0/10, Gi2/0/10 of Po10

[Joseph W. Doherty]

I recall (?) a 3750 supports src-dest-IP. If so, that's often the "best" choice.

I dunno about SG choices.

[mlund]

Hi

I may be misundertanding the topology, but if there are two portchannels between the same switches (3750 stack is one switch), then spanning-tree will block one of the port-channels to avoid a loop. If that the case then mostly control packet will update the counters.

/Mikael

[Fotiosmark]

Both switches are in Stack mode....
So 2 3750 Stack, and 2 SG stack. Each Gig port connects to each of the stack, so you have full Active links :)
So since all ports are active, from Po10 some traffice doesn't pass through.
Also the tests load balance, chooses only 1 link, shouldn't be both links?

[Jon Marshall]

But two etherchannels means two paths between the stacks so that is a loop which means one of the etherchannels must block surely ? 

Jon 

[Fotiosmark]

SW-ATH-FL-1-1#sh spanning-tree interface port-channel 7

Vlan Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
VLAN0001 Desg FWD 3 128.536 P2p
VLAN0005 Desg FWD 3 128.536 P2p
VLAN0011 Desg FWD 3 128.536 P2p
VLAN0012 Desg FWD 3 128.536 P2p
VLAN0017 Desg FWD 3 128.536 P2p
VLAN0018 Desg FWD 3 128.536 P2p
VLAN0020 Desg FWD 3 128.536 P2p
VLAN0022 Desg FWD 3 128.536 P2p
VLAN0023 Desg FWD 3 128.536 P2p
VLAN0024 Desg FWD 3 128.536 P2p
VLAN0025 Desg FWD 3 128.536 P2p
VLAN0026 Desg FWD 3 128.536 P2p
VLAN0030 Desg FWD 3 128.536 P2p
VLAN0055 Desg FWD 3 128.536 P2p
VLAN0100 Desg FWD 3 128.536 P2p


SW-ATH-FL-1-1#sh spanning-tree interface port-channel 10

Vlan Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
VLAN0001 Desg FWD 3 128.560 P2p
VLAN0005 Desg FWD 3 128.560 P2p
VLAN0011 Desg FWD 3 128.560 P2p
VLAN0012 Desg FWD 3 128.560 P2p
VLAN0017 Desg FWD 3 128.560 P2p
VLAN0018 Desg FWD 3 128.560 P2p
VLAN0020 Desg FWD 3 128.560 P2p
VLAN0022 Desg FWD 3 128.560 P2p
VLAN0023 Desg FWD 3 128.560 P2p
VLAN0024 Desg FWD 3 128.560 P2p
VLAN0025 Desg FWD 3 128.560 P2p
VLAN0026 Desg FWD 3 128.560 P2p
VLAN0030 Desg FWD 3 128.560 P2p
VLAN0055 Desg FWD 3 128.560 P2p
VLAN0100 Desg FWD 3 128.560 P2p

[Jon Marshall · Accepted solution]

STP only needs to block at one end and it looks like the 3750 is the root so all it's ports will be forwarding. 

Jon

[Fotiosmark]

offcourse...i feel s.....t now :)

[Joseph W. Doherty]

To further clarify (if needed) . . .

As Jon notes, if two port-channels (in the same L2 domain), STP would block one of them.

If two (or more) links in the same port-channel, STP doesn't block any, as they are considered one link.

Port-channels in different L2 domains or if routed , STP wouldn't block either.