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Subinterfaces Shutdown Issue Cisco 2821

Hi Guys

I have configured  a network. I have following equipments.

a) Cisco 3560 Switch

b) Cisco 2821 Router

There are two vlans configured on my switch named Vlan 2 and Vlan 3. I have configured port Gi0/8 on switch as trunk port. On router I have configured two subinterfaces which are Gi0/0.1 and Gi0/0.2 for Vlan 1 and Vlan 2. And routers Gi0/0 is connected to switch port Gi0/8.

a) Network (Vlan 3) is configured on On Gi0/0.2

b) Network (Vlan 2) is configured on On Gi0/0.1

Whenever I shutdown the subinterface Gi0/0.1, all the traffic of network also goes down. Please suggest some solution!!!!!!!!!!


When you say network 172.16.x

When you say network 172.16.x.x also goes down. What do you mean by that? How do you determine that? Is it not able to ping its gateway which is the sub interface address on the router? did you check if sub interface 2 stays up after shutting down sub interface 1?

you only mentioned 2 networks in your topology and if you shut down the logical routed port or gateway for one of them they won't be able to talk to each other. So I hope you are not trying to reach 192.168.x.x from 172.16.x.x after shutting the sub interface. 

Even after shutting the sub interface 192 168 X X should be able to talk to other hosts in that subnet and for the other network it should have reachability to its gateway. Make sure physical interface on the router that is connected to switch is up and so is the sub interface associated with 192 168 X X address. 

Please share the configuration of switch and router if you continue to have this issue and also the state of sub interface 2 after shutting down sub interface 1.

Community Member

It means that whenever I shut

It means that whenever I shut down the subinterface Gi0/0.1 which is for network, the other network also goes down. And that means users of that network can't access internet. They can perform interVlan routing in switch. But at router side they can't move forward to get access the internet.


I can't correlate these 2

I can't correlate these 2 networks until you share configuration. You mentioned users on network are only affected if sub interface for is shut down, so I am assuming when sub interface for is up users on network are able to access the internet, is this correct?

You didn't answer the question if users on 17.16.x.x network are able to ping the gateway for that subnet when sub interface for  is down.

Community Member

Yes users can ping the

Yes users can ping the gateway. By the way I resolved the issue. Thanks for your reply help. Really appreciable.

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