Etherchannel configuration

ivanka_busta · ‎04-28-2016

Hi,

Regarding the network diagram attached, I'm confused about port-channels 32 and 34. I don't understand how it can be working when the ports inside Po34 are trunk ports with native vlan 20 whereas the ports inside Po34 are configured just with the command switchport and apparently they just have vlan 1. When configuring port-channels, Don't they check the vlans, native vlan... on the neighboring switch?

All ports in Po34 are configured like this:

interface Ethernet1/3
description Po34
switchport mode trunk
switchport trunk native vlan 20
switchport trunk allowed vlan 20,81-83,91
channel-group 34 mode active

All ports in Po32 are configured like this:

interface GigabitEthernet2/21
description Nexus
switchport
storm-control broadcast level 5.00
no cdp enable
channel-group 32 mode active
end

This is what I get issuing the sh etherchannel summary on both switches:

Group Port-channel Protocol    Ports
------+-------------+-----------+-----------------------------------------------
32     Po32(SU)        LACP      Gi2/19(P)      Gi2/20(P)      Gi2/21(P)
                                 Gi2/22(P)

34 Po34(SU) Eth LACP Eth1/3(P) Eth1/4(P)

Thanks in advance.

Mark Malone · ‎04-28-2016

Hi

There 2 different port-channels can you post the other side too like e1/4 of po34 so we can see the full config setup

ivanka_busta · ‎04-28-2016

Hi,

Ports E1/3, E1/4 of both Nexus are configured like this:

interface Ethernet1/4
description Po34
switchport mode trunk
switchport trunk native vlan 20
switchport trunk allowed vlan 20,81-83,91
channel-group 34 mode active

Ports Gi2/19, Gi2/20, Gi2/21 and Gi2/22 on the Cisco 6500 are configured like this:

interface GigabitEthernet2/22
description Nexus
switchport
storm-control broadcast level 5.00
no cdp enable
channel-group 32 mode active
end

Thanks.

Mark Malone · ‎04-28-2016

Hi

There's nothing wrong with them they match perfectly as they should , e1/4 and 3 are part of same channel same config , same with 21 and 22 same config

Everything looks good

the port-channel is e1/3 and e1/4

34 Po34(SU) Eth LACP Eth1/3(P) Eth1/4(P)

interface Ethernet1/3
description Po34
switchport mode trunk
switchport trunk native vlan 20
switchport trunk allowed vlan 20,81-83,91
channel-group 34 mode active

interface Ethernet1/4
description Po34
switchport mode trunk
switchport trunk native vlan 20
switchport trunk allowed vlan 20,81-83,91
channel-group 34 mode active

ivanka_busta · ‎04-28-2016

Hi,

Ok, so it doesn't matter if the config doesn't match the config of the neighboring swith. I mean, I thought that if e1/4 and e1/3 on the Nexus are trunk ports then gi2/21 and gi2/22 on the Cisco 6500 should be trunks with the same native vlan. I had read the following in a CCNA book:

The list of items the switch checks includes the following:

• Speed

• Duplex

• Operational access or trunking state (all must be access, or all must be trunks)

• If an access port, the access VLAN

• If a trunk port, the allowed VLAN list

• If a trunk port, the native VLAN

• STP interface settings

In addition, switches check the settings on the neighboring switch. To do so, the switches either use PAgP or LACP (if already in use), or Cisco Discovery Protocol (CDP) if using manual configuration. The neighbor must match on all parameters in this list except the STP settings.

Last sentence is the one which make me feel confuse about the attached network topology.

Mark Malone · ‎04-28-2016

Hi

Are you saying that the cdp neighbours (directly connected neighbours ) for E1/3 and E/14 are the ports G1/22 and G1/22 ? so your saying po32 is connected to po34 ?

Because this ether channel output you posted you would think they were directly connected to the po32 highlighted lines below not the po34

Group Port-channel Protocol    Ports
------+-------------+-----------+-----------------------------------------------
32     Po32(SU)        LACP      Gi2/19(P)      Gi2/20(P)      Gi2/21(P)
                                 Gi2/22(P)

34 Po34(SU) Eth LACP Eth1/3(P) Eth1/4(P)

********************************************

To clear this up post remove the no cdp enable from the interfaces take a copy of the show cdp neighbours and show etherchannel summary from each side and post it , the portchannels cannot be different each side they wont bundle if the config is not correct and all of yours are working in P mode

I assumed looking at your outputs g1/21/. and g2/21 would be connected to g2/21 and g2/22

ivanka_busta · ‎04-28-2016

E1/3, E1/4, E1/3 and E1/4 of each of the Cisco Nexus are attached to Gi2/19, Gi2/20, Gi2/21 and Gi2/22 of the Cisco 6500 respectively (there's a network diagram attached). Yes, Po32 is attached to Po34.

This is the output of the show etherchannel summary on the Cisco 6500:

Group Port-channel Protocol    Ports
------+-------------+-----------+-----------------------------------------------
32     Po32(SU)        LACP      Gi2/19(P)      Gi2/20(P)      Gi2/21(P)
                                 Gi2/22(P)

This is the output of the show etherchannel summary on the Cisco Nexus:

--------------------------------------------------------------------------------
Group Port-       Type     Protocol Member Ports
      Channel
--------------------------------------------------------------------------------
34    Po34(SU)    Eth      LACP      Eth1/3(P)    Eth1/4(P)

Enabling cdp on port 2/19 on the Cisco 6500 I get this:

show cdp neighbors gigabitEthernet 2/19
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone

Device ID Local Intrfce Holdtme Capability Platform Port ID
H-4717(FOC1926R1SB)
Gig 2/19 174 R S I N3K-C3064 Eth 1/3

Thank you so much for your help!

Mark Malone · ‎04-29-2016

Ok that's strange there bundled but I cant see how it would work one side trunk and one side access , any traffic from trunk side will be dropped but I can see how its probabaly working overall still as looking at your diagram the po31,33 looks to be set correctly which would mean theres still a correct path between between the 65s and the Nexus switches have a crossbar as well between them

You do know as well the Nexus side can be set as VPC and the 6500 side can be a normal port-channel this will give you better resiliency in configuration

I cant answer why that channel has formed with incorrect parameters each side maybe its to do with being IOS and NX-OS and both sides are set active LACP trying to negotiate up and not active/passive or maybe software issue, I don't see how it can be working though for those port-channels that do not match , if you drop po31,33 I don't think you will get traffic between the devices anymore

If that was my setup and I have a similar multiple setups as our DCs bridge our production networks setup I would vpc the Nexus side and fix the port-channels on 34/32 its like someone half set them up , I cant see what the valid reason would be behind that unless there specifically trying to block traffic

Have a look at this doc for recommended setup just search 6500 shows you the way it should be set in terms of design with vpc setup , you may as well make use of the capability as its major selling point of the nexus switches for resiliency

http://www.cisco.com/c/en/us/td/docs/switches/datacenter/sw/4_2/nx-os/interfaces/configuration/guide/if_nxos/if_vPC.pdf

ivanka_busta · ‎04-29-2016

Hi,

Thank you so much for your help. We would try to fix the port-channels on 34/32.

Martin Houde · ‎04-28-2016

Hi Ivanka,

You need to disable BPDU's on the catalyst 6500 for those specific ports. As soon as the Nexus see's a BPDU it puts the port in Err-Disable state since these are meant to be configured as Edge Ports.

EDIT: Spoke too soon, doesn't look like you're using any downstream FEX, and ports are not in Err-Disable. Sorry for the confusion!

Best of luck!

Martin