Enable trunking from cisco3825 router to cisco 3560 switch

Unanswered Question
Oct 20th, 2008
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i am relatively new,so i would like to know how to enable trunking from 3825 router to 3560 switch.

If i am missing any details please let me know.

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Overall Rating: 5 (2 ratings)
singhsaju Mon, 10/20/2008 - 11:35
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You can create subinterfaces(corresponding to each vlan) on the router's fastethernet port and configure the port (on the switch) attached to this router as trunk port.



int fas 0/0

speed 100

duplex full

int fas 0/0.10

descr VLAN 10 interface

encap dot1q 10

ip address

int fas 0/0.20

descr VLAN 20 interface

encap dot1q 20

ip address

int fas 0/0.30

descr VLAN 30 interface

encap dot1q 30

ip address

On Switch


int fas 0/1

description Connected to Cisco 3845 fas0/0

switchport mode trunk

switchport trunk encap dot1q



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Giuseppe Larosa Mon, 10/20/2008 - 11:40
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Hello Ravishankar,

the trunk is configured on the switch side

on the router side for each Vlan where the router has to be member of you configure a vlan subif.

the same trunking method 802.1Q or ISL must be used on both sides

if using 802.1Q the native vlan (=untagged) must match default is vlan 1 on both.

for the switch side use:


for the router side:

int f0/0

no ip address

int f0/0.10

enc dot1q 10

ip addr

int f0/0.20

enc dot1q 20

ip addr

Hope to help


rkatikireddy Tue, 10/21/2008 - 05:46
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thanks for your quick response and it was very elaborative.

Here is the deal,these two devices(3825 and 3560(24port) are new devices and i have to configure them so they are good to be used for voip.

what are the basic configurations i need on them.

If you can give me step by step,that would be really nice of you.

I have to add a default route on 3825 which would be the ip address of a wan router.

And how would i enable dhcp on both the devices.

Like i mentioned,i am totally new to devices and your help would help me understand at this learning stage.


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