Confusing VLANs on 1941 router with VLANs on c3650 Switch?

[StefanA.]

Hi

I'm struggling to configure VLAN trunks from my 1941 Router to my C3650 Switch.

Configuring VLAN on the switch seems to work. All systems at ports in VLAN1 can communicate with each other and they can not communicate with the systems in VLAN2.
To route between these two VLANs, I have configured a Port as trunk, where I've connected my 1941 Router to. On the router, I have configured a Gig interface with two sub interfaces ....

The relevant parts in my configuration:

C1941:
-----------------------------------------------------
vlan ifdescr detail
multilink bundle-name authenticated
license udi pid CISCO1941/K9 sn FCZ.....P

interface GigabitEthernet0/0
description Managment Address
no ip address
duplex auto
speed auto
!
interface GigabitEthernet0/0.1
encapsulation dot1Q 1 native
ip address 10.1.1.1 255.255.255.0
!
interface GigabitEthernet0/0.2
encapsulation dot1Q 2
ip address 10.2.2.2 255.255.255.0
!

ip route 0.0.0.0 0.0.0.0 10.1.1.2
-----------------------------------------------------

C3650:
-----------------------------------------------------
spanning-tree mode pvst
spanning-tree extend system-id
!
vlan internal allocation policy ascending
!
interface GigabitEthernet0/1
switchport mode access
spanning-tree portfast
!
interface GigabitEthernet0/2
switchport mode access
spanning-tree portfast
!
interface GigabitEthernet0/3
switchport access vlan 2
switchport mode access
spanning-tree portfast
!
interface GigabitEthernet0/4
switchport access vlan 2
switchport mode access
spanning-tree portfast
...
!
interface GigabitEthernet0/45
description Trunk to Router
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,2
switchport mode trunk
!
interface Vlan1
ip address 10.1.1.109 255.255.255.0
!
ip default-gateway 10.1.1.2
-----------------------------------------------------

On the PC systems, the relevant next hop is the router's IP of that segment.

As mentioned,
- I can access systems within VLAN1 (Gig0/1 <-> 0/2) or within VLAN2 (Gig0/3 <-> 0/4)
- I can not access from e.g. system at Gig0/1 to 0/4 which would have to cross the router.

So I expect my trunk configuration is odd, but can not find any reason.

On the Switch, it looks like this:

Switch-RACK#sh vlan id 1
VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Gi0/1, Gi0/2, Gi0/5, Gi0/6
Gi0/7, Gi0/8, Gi0/9, Gi0/10
Gi0/11, Gi0/12, Gi0/13, Gi0/14
Gi0/15, Gi0/16, Gi0/17, Gi0/18
Gi0/19, Gi0/20, Gi0/21, Gi0/22
Gi0/23, Gi0/24, Gi0/25, Gi0/26
Gi0/27, Gi0/28, Gi0/29, Gi0/30
Gi0/31, Gi0/32, Gi0/33, Gi0/34
Gi0/35, Gi0/36, Gi0/37, Gi0/38
Gi0/39, Gi0/40, Gi0/41, Gi0/42
Gi0/43, Gi0/44, Gi0/45, Gi0/46
Gi0/47, Gi0/48, Gi0/49, Gi0/50
Gi0/51, Gi0/52

Switch-RACK#sh vlan id 2
VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
2 Privat active Gi0/3, Gi0/4, Gi0/45

Any ideas are appreciated.

Thanks
Stefan

[balaji.bandi · Accepted solution]

what is this IP ?

10.1.1.2

on switch

ip default-gateway 10.1.1.1
or 
ip route 0.0.0.0 0.0.0.0 10.1.1.1

If you looking inter VLAN communication, you do not need router, switch is good enough to take care.

can you post show vlan from switch.,

example :

https://www.cisco.com/c/en/us/support/docs/lan-switching/inter-vlan-routing/14976-50.html

[StefanA.]

HI,

thanks for your quick reply.

10.1.1.2 is the gateway to the internet firewall.

Your link to the document helped a lot!

Although my configuration was looking quite similar, there is a note in the document

!-- In case of dot1q, you need to make sure that the native VLAN matches across the link.

in the show interface switchport command, I found

Trunking Native Mode VLAN: none

 I ran the interface command to align with the document's recommendations

switchport trunk native vlan 1

and it worked.

Running the show interface switchport command again showed

Trunking Native Mode VLAN: 1 (default)

...although it does not show any additional config lines...
but anyway, as it claims to be the default, I'm fine.

Again. Thank you very much.