Trunk VLANs – How to Trunk VLANs Over Layer 3 EtherChannel

ciscocisco-catalystetherchannellayer3vlan

I am trying to setup a network that includes an EtherChannel link between two Cisco Layer 3 switches (Catalyst 3750). I am using a collapsed core hierarchical network.

collapsed core topology

The picture above is my topology. On my layer 2 access switches (S1, S2, S3) I have several hosts connected right now, on several VLANs.
My issue tho is that a host on for example S2, can't communicate with L3-1 through the EtherChannel between L3-1 and L3-2. I've tried making it a Layer 3 EtherChannel with IP's, and I can ping across, but it's like it wont propagate my tagged VLAN traffic.

Example:

I connect HOST-A to L3-1 on interface GigabitEthernet2/0/1.

I make GigabitEthernet2/0/1 switchport access on VLAN 20.

HOST-B is connected to a switchport access VLAN 20 port on S2.

HOST-B tries to ping L3-2. Succesful.

HOST-B tries to ping across to L3-1 / HOST-A. Not succesful.

PS. I also have HSRP setup on the Layer 3 switches, for all my VLANs. Also I have a Main Windows Server 2016 Domain Controller connected to L3-1 and a Backup connected to L3-2.

Let me know if you need the IP scope.

I appreciate all help! I just want to know what I have to think of/be sure of is working, to make this network communicate. Any help that can guide me to what i can do to get traffic all the way to the WAN, and so that my hosts on S1, S2 and S3 can connect to the internet. Much appreciated.

CONFIGURATION:

L3-1

Port-Channel:

!
interface Port-channel1
 no switchport
 ip address 172.16.0.1 255.255.255.252
!
!
interface GigabitEthernet2/0/19
 no switchport
 no ip address
 channel-group 1 mode desirable
!
interface GigabitEthernet2/0/20
 no switchport
 no ip address
 channel-group 1 mode desirable
!

L3-2 has same configuration on same ports and channel-group. It's IP address is 172.16.0.2 255.255.255.252 instead.

VLAN-config:
show vlan brief in cisco terminal

All links between layer-3 and layer-2 switches are trunks. A snippet from L3-2:
interface overview from layer 3 switch

S1

VLAN-config:
vlan overview on switch

S2

VLAN-config:
vlan overview on switch

S3

VLAN-config:
vlan overview on switch

Best Answer

@RoyT. On your links between L3-1 and L3-2, how come you don't use a normal trunked etherchannel? Does the 172.16.0.1 255.255.255.252 have any purpose?

For instance, if you put this configuration on the interlink between L3-1 and L3-2:

interface Port-channel1
 switchport
 switchport trunk encapsulation dot1q
 switchport mode trunk
!
interface GigabitEthernet2/0/19
 switchport
 switchport trunk encapsulation dot1q
 switchport mode trunk
 channel-group 1 mode desirable
!
interface GigabitEthernet2/0/20
 switchport
 switchport trunk encapsulation dot1q
 switchport mode trunk
 channel-group 1 mode desirable
!

Then everything will be able to communicate.

In order to do it:

(config)# int range gi2/0/19-20
(config-if)# no channel-group
(config-if)# switchport
(config-if)# switchport trunk encapsulation dot1q
(config-if)# switchport mode trunk
(config-if)# int po1
(config-if)# no ip address
(config-if)# switchport
(config-if)# switchport trunk encapsulation dot1q
(config-if)# switchport mode trunk
(config-if)# int range gi2/0/19-20
(config-if)# channel-group 1 mode desirable
(config-if)# end
# write memory
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