Nexus 7k - vPC - downstream port-channels

[azlatkin]

I have a pair of Nexus 7k configured for virtual port-channel (with domain, peer-links, pkal, etc.)

I have three Nexus 5k switches dowstream, that I want to connect to both 7k using vPC.

From the documentation I understand that I must use port-channels on both 7k to attach downsream

switches. But it is not clear to me whether I must use separate port-channel for each downstream

switch, or I may bundle all downsream links into a common port-channel on 7k?

E.g., with separate port-channels on N7k-1:

interface ethernet 7/1-2
description to N5k-1
switchport mode trunk
allowed vlan 1-50
channel-group 51 mode active
!
interface port-channel 51
vpc 50
!

interface ethernet 7/9-10
description to N5k-2

switchport mode trunk
allowed vlan 1-50
channel-group 52 mode active
!
interface port-channel 52
vpc 50

Or, with a common port-channel:

interface ethernet 7/1-2
description to N5k-1
switchport mode trunk
allowed vlan 1-50
channel-group 50 mode active

!

interface ethernet 7/9-10
description to N5k-2

switchport mode trunk
allowed vlan 1-50
channel-group 50 mode active
!
interface port-channel 51
vpc 50
--------------------------------

[allan.thomas · Accepted solution]

As this post is now a couple of days ago you may have already discovered the answer.  However, the vPC requires a unique Port-Channel group for each downstream device between the vPC peer devices, the two N7Ks in this case.  Essentially you need to configure three port-channels, one for each of your downstream N5Ks on both your N7K vPC peer devices:-

For example:-

N7K-1

interface ethernet 7/1-2
description to N5k-1
switchport mode trunk
switchport trunk allowed vlan 1-50
channel-group 100 mode active
!
interface port-channel 100
vpc 100
!

N7K-2

interface ethernet 7/1-2
description to N5k-1
switchport mode trunk
switchport trunk allowed vlan 1-50
channel-group 100 mode active
!
interface port-channel 100
vpc 100

!

N7K-1

interface ethernet 7/9-10
description to N5k-2

switchport mode trunk
switchport trunk allowed vlan 1-50
channel-group 101 mode active
!
interface port-channel 101
vpc 101

N7K-2

interface ethernet 7/9-10
description to N5k-2

switchport mode trunk
switchport trunk allowed vlan 1-50
channel-group 101 mode active
!
interface port-channel 101
vpc 101

.

.

.

.

etc.

Hope this helps

Allan.

[azlatkin]

Thank you Allan.

In fact the answer to my question is: Both possible.

-- Separate downstream port-channel (and vpc) per each attached device (as you propose).

-- And common downstream port-channel (and vpc) for a pair of attached N5k on condition

this pair is also configured for vPC. The latter topo is called Double-sided vPC or sometimes

back-to-back vPC, and it uses common vpc id and common Po's between all 4 devices.

The Double-sided vPC has an important advantage (over the topo with separate port-channels)

of permitting port-channel teaming for the hosts dual-homed to n5k's (i.e.load-balancing).

alex

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