Nexus 5K & 2K Link Aggregation (vPC)

ciscomanx · ‎02-07-2012

Hi Guys,

Just want to get your expert opinion on this. I configured port-channel & vPC on two separate Nexus switch. The configuration is correct as the vPC is up and are port-channeling. The only thing I noticed is the aggregated bandwidth or link speed on the vPC as shown on the verification below. It does not show the aggregated BW which should be 2000000 Kbit in this case because I bundled two 1Gbe interfaces from diferent Nexus switches.

vPC is define as: "A virtual port channel (vPC) allows links that are physically connected to two different Cisco Nexus 5000 Series switches to appear as a single port channel to a third device."

My questions is, does vPC aggregates the bandwidth or speed accross multiple physical switches? Why it wasn't shown on the "show vpc" result as aggregated bandwidth?

Just curious and I wonder if I missed something on the configuration.

Configuration on Switch-1:

interface port-channel100
switchport mode trunk
vpc 100
switchport trunk allowed vlan 12-14
duplex full

interface Ethernet100/1/1
switchport mode trunk
switchport trunk allowed vlan 12-14
duplex full
channel-group 100

Configuration on Switch-2:

interface port-channel100
switchport mode trunk
vpc 100
switchport trunk allowed vlan 12-14
duplex full

interface Ethernet100/1/1
switchport mode trunk
switchport trunk allowed vlan 12-14
duplex full
channel-group 100

Verification on Switch-1:

N5K-01# show vpc statistics vpc 100

port-channel100 is up

vPC Status: Up, vPC number: 100

Hardware: Port-Channel, address:

Description:

MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA

Port mode is trunk

full-duplex, 1000 Mb/s

Beacon is turned off

Input flow-control is off, output flow-control is on

Switchport monitor is off

EtherType is 0x8100

Members in this channel: Eth100/1/1

Verification on Switch-2:

N5K-02# show vpc statistics vpc 100
port-channel100 is up
vPC Status: Up, vPC number: 100
Hardware: Port-Channel, address:
Description:
MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA
Port mode is trunk
full-duplex, 1000 Mb/s
Beacon is turned off
Input flow-control is off, output flow-control is on
Switchport monitor is off
EtherType is 0x8100
Members in this channel: Eth100/1/1

I appreciate and welcomed your comments. Thanks.

Richard

Oleksandr Nesterov · ‎02-09-2012

Hi

As it comes - nexus reports about aggregated bandwidth of local VPC members. SO if you'd have 2 1gig links on this chassis and 2 1gig links - on the other - total bandwidtch would be 2000000 Kbit.

Same behavior on n5k and n7k platforms.

As for aggregating the bandwidth - vpc works as portchannel - so traffic which came to vpc cluster will be balanced between vpc links.

That means that your downstream device will use whole bandwidth loadbalancing between port-chanel members.

HTH,

Alex

Devavrat Oka · ‎05-23-2012

Remember a downstream device sees the two Nexus switches as a single logical device, but it still uses 'port-channel' and not 'virtual port-channel' to the upstream device. The vPC is only between the two Nexus 5k switches.

vPC actively forwards on both links. Hence it uses up all the uplink bandwidth.