Why interface VLAN doesn't come up if there is no access port configured with VLAN=i/f VLAN and only trunks ports are configured

[ashish7aditya]

Hello Experts,

I have noticed that interface VLAN doesn't come up till the time I configure one of the switch port as access with VLAN = i/f VLAN & connect one end device like PC through it.

I have two switched connected as below:

switch#1 --------- switch#2---PC#1

I have configured interface VLAN#2 on switch#1 and #2 and have allowed VLAN#1-2 over the trunk link between two switches. I see interface VLAN doesn't come up (even I have changed the native VLAN from 1 to 2 on each switch).

Now moment I connect PC#1 on one of the access port(under VLAN#2) of switch#2, interface VLAN of switch#2 comes UP, however i/f VLAN for switch#1 is still down.

Why interface VLAN comes UP only after I generate a traffic from any local access port of that switch (under same VLAN = i/f VLAN). Why even after connecting PC#1, i/f VLAN on switch#1 was still down and no communication happens between PC#1 and switch#1?

Best Regards!

[Vasilii Mikhailovskii]

Hello.

I'm not sure what do you see on your devices.

The issue may come from VTP prune (so, disable it).

The best way to check L2 is:

 - show ip int vl ...
 - show span vl ...
 - show vlan id ..
 - show int trunk

Please provide the outputs from both switches.

[ashish7aditya]

Hello Vasilii/ Other Experts,

Good day.

Actually, I was just performing one practice exercise on packet tracer(diagram attached).

I have connected one switch(SW#16 in the attached diagram) from HWIC card(switch i/f of Router11) and have configured two interface VLANS. i.e. VLAN#2(IP 10.1.1.1/8) & interface VLAN#3(IP 11.1.1.1/8) on this router#11and I have configured switch#16 with interface VLAN#2(IP add DHCP) and further I have connected one PC from access port(VLAN#3) of switch#16. Again IP assignment for this PC is set as DHCP.

Router#10 was set as DHCP server and RIPv2 on both the routers was enabled along with DHCP helper IP on Router11 for each interface.

The PCs which are connected from Gi0/1 & Gi0/2 of router11 receives IPs from DHCP server, however, interface VLAN of switch 16 and PC41(connected from switch#16) doesn't receive IPs.

Then I realised that although I have defined VLAN#2 & VLAN#3 on HWIC(R11) but both the VLANs are operationally and admin down. I tried no shutdown under each i/f VLAN but still they don't come up.

I know if I am working on any of the native switch example 2960, moment I create VLAN#2 and then I change the i/f VLAN to VLAN#2, it's status comes UP. But with HWIC card in the router, it doesn't come up.

any Idea why ? and where I am wrong or missing any point?

I think maybe because we can't create VLANs on the router(2911) and thus, it need some external chatty device to come up and for this, moment I connect any PC through that switch under access VLAN = i/f VLAN, i/f VLAN comes up.

Best Regards!