Layer 2 Load Balancing

[Muhammad Kamran Shahzad]

Dear Experts,

Looking for solution to implement load balancing which I have done using Rapid-PVST.

I have 4 Uplinks in Cisco WS-C3750G-24PS Switch.

All traffic is Layer 2 traffic destined towards PPPoE Server behind.

I have my clients connected from Interface Gi 1/01-24 and Uplinks are Gi 1/0/25-28.

I have done some load balancing which works well but the issue I am facing is that Switch is not giving throughput more then 1Gbps.

Please note I cannot configure Port Channel as all links are coming from different switches from upstream

Interfaces from Gi 1/0/25 to Int Gi 1/0/28 configured as Trunk and 1Gbps full duplex speed.

All links have enough capacity of 1Gbps each but switch is not providing more then 1Gbps speed.

Could you please advise and see below configuration of Uplink ports and there STP status.

cisco WS-C3750G-24PS (PowerPC405) processor (revision H0) with 131072K bytes of memory.
Processor board ID FOC1418Y48E
Last reset from power-on
2 Virtual Ethernet interfaces
28 Gigabit Ethernet interfaces
The password-recovery mechanism is enabled.

512K bytes of flash-simulated non-volatile configuration memory.
Base ethernet MAC Address : AC:A0:16:8A:F2:00
Motherboard assembly number : 73-10217-08
Power supply part number : 341-0108-04
Motherboard serial number : FOC14185HC9
Power supply serial number : DCA1417A3A0
Model revision number : H0
Motherboard revision number : C0
Model number : WS-C3750G-24PS-S
System serial number : FOC1418Y48E
Top Assembly Part Number : 800-26855-02
Top Assembly Revision Number : E0
Version ID : V06
CLEI Code Number : COMXD00ARA
Hardware Board Revision Number : 0x09

interface GigabitEthernet1/0/25
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree vlan 1,121-135,253 cost 2000
spanning-tree vlan 111-120,136-140 cost 5000
end

interface GigabitEthernet1/0/26
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree vlan 1,111-135,139,253 cost 5000
spanning-tree vlan 136-138,140 cost 2000
end

interface GigabitEthernet1/0/27
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree vlan 1,114-140,253 cost 5000
spanning-tree vlan 111-113 cost 2000
end

interface GigabitEthernet1/0/28
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree vlan 1 cost 50000
spanning-tree vlan 111-113,121-138,140,253 cost 5000
spanning-tree vlan 114-120,139 cost 2000
end

See below STP status and pathcost method is long.

sh spanning-tree interface gigabitEthernet 1/0/25

Vlan Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
VLAN0001 Desg FWD 2000 128.25 P2p
VLAN0111 Altn BLK 5000 128.25 P2p
VLAN0112 Altn BLK 5000 128.25 P2p
VLAN0113 Altn BLK 5000 128.25 P2p
VLAN0114 Altn BLK 5000 128.25 P2p
VLAN0115 Altn BLK 5000 128.25 P2p
VLAN0116 Altn BLK 5000 128.25 P2p
VLAN0117 Altn BLK 5000 128.25 P2p
VLAN0118 Altn BLK 5000 128.25 P2p
VLAN0119 Altn BLK 5000 128.25 P2p
VLAN0120 Altn BLK 5000 128.25 P2p
VLAN0121 Root FWD 2000 128.25 P2p
VLAN0122 Root FWD 2000 128.25 P2p
VLAN0123 Root FWD 2000 128.25 P2p
VLAN0124 Root FWD 2000 128.25 P2p
VLAN0125 Root FWD 2000 128.25 P2p
VLAN0126 Root FWD 2000 128.25 P2p
VLAN0127 Root FWD 2000 128.25 P2p
VLAN0128 Root FWD 2000 128.25 P2p
VLAN0129 Root FWD 2000 128.25 P2p
VLAN0130 Root FWD 2000 128.25 P2p
VLAN0131 Root FWD 2000 128.25 P2p
VLAN0132 Root FWD 2000 128.25 P2p
VLAN0133 Root FWD 2000 128.25 P2p
VLAN0134 Root FWD 2000 128.25 P2p
VLAN0135 Root FWD 2000 128.25 P2p
VLAN0136 Altn BLK 5000 128.25 P2p
VLAN0137 Altn BLK 5000 128.25 P2p
VLAN0138 Altn BLK 5000 128.25 P2p
VLAN0139 Altn BLK 5000 128.25 P2p
VLAN0140 Altn BLK 5000 128.25 P2p
VLAN0253 Root FWD 2000 128.25 P2p

sh spanning-tree interface gigabitEthernet 1/0/26

Vlan Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
VLAN0001 Root FWD 5000 128.26 P2p
VLAN0111 Altn BLK 5000 128.26 P2p
VLAN0112 Altn BLK 5000 128.26 P2p
VLAN0113 Altn BLK 5000 128.26 P2p
VLAN0114 Altn BLK 5000 128.26 P2p
VLAN0115 Altn BLK 5000 128.26 P2p
VLAN0116 Altn BLK 5000 128.26 P2p
VLAN0117 Altn BLK 5000 128.26 P2p
VLAN0118 Altn BLK 5000 128.26 P2p
VLAN0119 Altn BLK 5000 128.26 P2p
VLAN0120 Altn BLK 5000 128.26 P2p
VLAN0121 Altn BLK 5000 128.26 P2p
VLAN0122 Altn BLK 5000 128.26 P2p
VLAN0123 Altn BLK 5000 128.26 P2p
VLAN0124 Altn BLK 5000 128.26 P2p
VLAN0125 Altn BLK 5000 128.26 P2p
VLAN0126 Altn BLK 5000 128.26 P2p
VLAN0127 Altn BLK 5000 128.26 P2p
VLAN0128 Altn BLK 5000 128.26 P2p
VLAN0129 Altn BLK 5000 128.26 P2p
VLAN0130 Altn BLK 5000 128.26 P2p
VLAN0131 Altn BLK 5000 128.26 P2p
VLAN0132 Altn BLK 5000 128.26 P2p
VLAN0133 Altn BLK 5000 128.26 P2p
VLAN0134 Altn BLK 5000 128.26 P2p
VLAN0135 Altn BLK 5000 128.26 P2p
VLAN0136 Root FWD 2000 128.26 P2p
VLAN0137 Root FWD 2000 128.26 P2p
VLAN0138 Root FWD 2000 128.26 P2p
VLAN0139 Altn BLK 5000 128.26 P2p
VLAN0140 Root FWD 2000 128.26 P2p
VLAN0253 Desg FWD 5000 128.26 P2p

#sh spanning-tree interface gigabitEthernet 1/0/27

Vlan Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
VLAN0001 Desg FWD 5000 128.27 P2p
VLAN0111 Root FWD 2000 128.27 P2p
VLAN0112 Root FWD 2000 128.27 P2p
VLAN0113 Root FWD 2000 128.27 P2p
VLAN0114 Altn BLK 5000 128.27 P2p
VLAN0115 Altn BLK 5000 128.27 P2p
VLAN0116 Altn BLK 5000 128.27 P2p
VLAN0117 Altn BLK 5000 128.27 P2p
VLAN0118 Altn BLK 5000 128.27 P2p
VLAN0119 Altn BLK 5000 128.27 P2p
VLAN0120 Altn BLK 5000 128.27 P2p
VLAN0121 Altn BLK 5000 128.27 P2p
VLAN0122 Altn BLK 5000 128.27 P2p
VLAN0123 Altn BLK 5000 128.27 P2p
VLAN0124 Altn BLK 5000 128.27 P2p
VLAN0125 Altn BLK 5000 128.27 P2p
VLAN0126 Altn BLK 5000 128.27 P2p
VLAN0127 Altn BLK 5000 128.27 P2p
VLAN0128 Altn BLK 5000 128.27 P2p
VLAN0129 Altn BLK 5000 128.27 P2p
VLAN0130 Altn BLK 5000 128.27 P2p
VLAN0131 Altn BLK 5000 128.27 P2p
VLAN0132 Altn BLK 5000 128.27 P2p
VLAN0133 Altn BLK 5000 128.27 P2p
VLAN0134 Altn BLK 5000 128.27 P2p
VLAN0135 Altn BLK 5000 128.27 P2p
VLAN0136 Altn BLK 5000 128.27 P2p
VLAN0137 Altn BLK 5000 128.27 P2p
VLAN0138 Altn BLK 5000 128.27 P2p
VLAN0139 Altn BLK 5000 128.27 P2p
VLAN0140 Altn BLK 5000 128.27 P2p
VLAN0253 Desg FWD 5000 128.27 P2p

sh spanning-tree interface gigabitEthernet 1/0/28

Vlan Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
VLAN0001 Desg FWD 50000 128.28 P2p
VLAN0111 Altn BLK 5000 128.28 P2p
VLAN0112 Altn BLK 5000 128.28 P2p
VLAN0113 Altn BLK 5000 128.28 P2p
VLAN0114 Root FWD 2000 128.28 P2p
VLAN0115 Root FWD 2000 128.28 P2p
VLAN0116 Root FWD 2000 128.28 P2p
VLAN0117 Root FWD 2000 128.28 P2p
VLAN0118 Root FWD 2000 128.28 P2p
VLAN0119 Root FWD 2000 128.28 P2p
VLAN0120 Root FWD 2000 128.28 P2p
VLAN0121 Altn BLK 5000 128.28 P2p
VLAN0122 Altn BLK 5000 128.28 P2p
VLAN0123 Altn BLK 5000 128.28 P2p
VLAN0124 Altn BLK 5000 128.28 P2p
VLAN0125 Altn BLK 5000 128.28 P2p
VLAN0126 Altn BLK 5000 128.28 P2p
VLAN0127 Altn BLK 5000 128.28 P2p
VLAN0128 Altn BLK 5000 128.28 P2p
VLAN0129 Altn BLK 5000 128.28 P2p
VLAN0130 Altn BLK 5000 128.28 P2p
VLAN0131 Altn BLK 5000 128.28 P2p
VLAN0132 Altn BLK 5000 128.28 P2p
VLAN0133 Altn BLK 5000 128.28 P2p
VLAN0134 Altn BLK 5000 128.28 P2p
VLAN0135 Altn BLK 5000 128.28 P2p
VLAN0136 Altn BLK 5000 128.28 P2p
VLAN0137 Altn BLK 5000 128.28 P2p
VLAN0138 Altn BLK 5000 128.28 P2p
VLAN0139 Root FWD 2000 128.28 P2p
VLAN0140 Altn BLK 5000 128.28 P2p
VLAN0253 Desg FWD 5000 128.28 P2p

[Joseph W. Doherty]

Generally, for a single flow, you only obtain one link's bandwidth.

On a router, with multiple (L3) links, they often support packet by packet LB, but its side effects are such it's generally not recommended for common usage.

For L2, there are some technologies that will use multiple links per flow, but often not for high bandwidth Ethernet.

[Muhammad Kamran Shahzad]

Hi Joseph,

Thanks for reply.
I can confirm all of the links are utilizing as per configured STP Pathcost.

But switch it self not providing bandwidth more then 1Gbps.
So all of the links are active and transmitting packets towards PPPoE Server but switch is not providing more then 1Gbps throughput.

Thanks

[Joseph W. Doherty]

Again, if switch ports re gig, any specific flow will not take advantage of multiple links, and so, for any one flow, you'll not obtain more than gig throughput.

If you're doing LB via PVST, any particular VLAN will also be limited to using just one link.

Etherchannel and/or L3 can LB across multiple links, but they too, again, often limit any specific flow to one link's capacity.

[Muhammad Kamran Shahzad]

Thanks for calrifications.

So if Switch ports are Gig ports and also if flow is same as like in my case flow from different uplinks ports destined towards same PPPoE Server so it will not provide more then 1Gbps throughput even using multiple vlans.
Also advise if we replace switch with any switch which will be having 10Gbps uplink ports but we will connect 1Gbps SFP's. Will it provide throughput more then 1Gbps ?

As I do have Nexus 3048TP Switch.
Required your recommendation to achieve more utilization along with link redundancy as using Rapid-PVST for redundancy

Thanks

[MHM Cisco World]

It can router have throughput 1gbps and this effect SW behind.

Did you check Router license?

MHM

[Muhammad Kamran Shahzad]

Hi MHM,

Sorry didn't get you on this.

I have only switches until PPPoE Server.
Below is the traffic route from PPPoE Server to my Switch

PPPoE Server > Upstream Switch 1 > My Switch

PPPoE Server > Upstream Switch 2 > My Switch

PPPoE Server > Upstream Switch 3 > My Switch

PPPoE Server > Upstream Switch 4 > My Switch

So My switch is connected with 4 different switches and all layer 2 traffic going towards same pppoe server on vlan 111-140

Please advise

[MHM Cisco World]

All pppoe client use same vlan tag 

Or 

Each subset of clients use different vlan tag?

MHM