Difficulty Understanding Trunk Port Configuration on Router

[ciscoloveronetwothree]

Hello everyone, I am still a beginner and I'm trying to configure a network with predefined information in Cisco Packet Tracer, as seen below. However, I've never worked with this kind of configuration, my guess is that this is a trunk port on a router, but I don't know how to configure it correctly. Any guidance would be greatly appreciated. 

[Kasun Bandara]

@ciscoloveronetwothree hi, this is names as router on stick configuration. actually its not trunk on router interface. you just creating sub interfaces on router interface. this guide will help to understand concept and configuration.

https://networklessons.com/cisco/ccna-routing-switching-icnd1-100-105/how-to-configure-router-on-a-stick

[Joseph W. Doherty]

Yup, it's the router L3 version of a switch L2 trunk and can be used to work with a switch L2 trunk (BTW can be used for other things too).

@Kasun Bandara reference would likely be helpful as it shows how to use this in a router-on-a-stick situation, which, BTW, your topology is not (totally).

[Martin L]

Try it by yourself first; if still not good, you can attach your PT file here in a zip format.

Regards, ML
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[Giuseppe Larosa]

Hello @ciscoloveronetwothree ,

the LAN switch side has to be configured as a L2 802.1Q trunk carrying allowing VLANs 1 (native), 10,25,99.

On the router side you have VLAN based subinterfaces , each of them is a logical L3 interface with a different IP address and encapsulation.

The L2 encapsulation describes how to distinguish frames for each of the subinterfaces

frames with with a VLAN tag ID of 10 will be sent to logical interface with encapsulation dot1q 10 and so on.

to be noted the subinterface number does not need to be equal to the VLAN-ID but it is common practice to use the same value to make configuration clear to read.

int gi0/1

no ip address

int gi0/1.10

enc dot1q 10

ip address 172.16.10.254 255.255.255.0

int gi0/1.25

enc dot1q 25

ip address 172.16.25.254 255.255.255.0

int gi0/1.99

enc dot1q 99

ip address 172.16.99.254 255.255.255.0

to be noted untagged ethernet frames are processed by main interface gi0/1 the physical one.

The main interface can have an IP address configured

Hope to help

Giuseppe