Original subtitles

To set up communication between switch 1 and switch 2

these ports needs to be configured as a trunk port

I’m also gonna configure this port as trunk port

so that we can capture traffic

and see the encapsulated frames between the switches.

Starting with switch 1 the first thing I’m gonna do is to make everything static

so switchport mode access on gigabit 0/0

and then switchport nonegotiate to disable DTP to something similar

on gigabit 0/1 switchport mode access switchport nonegotiate. 10

do sh run 11

so this port 0/0 is configured as an access port in VLAN 1 DTP is disabled. 12

Gigabit 0/1 is configured as an access port in VLAN 2, DTP is disabled. 13

So we now need to configure ports 2 and 3 as trunk ports and disable DTP 14

so int g0/2 switchport mode trunk 15

and it’s gonna fail as you can see there 16

because we have to type switchport trunk encapsulation 17

and in this example we'll use dot1q 18

and then switchport mode trunk to make it a trunk port. 19

A trunk port allows multiple VLANs to traverse that port 20

switchport nonegotiate let’s do something similar 21

on port 3 set the encapsulation to dot1q 22

set the mode to trunk, disabled DTP and then I'll no shut those 2 ports. 23

So sh int g0/2 switchport 24

This command shows us that gigabit 0/2 is enabled as a layer 2 interface 25

it's been administratively configured as a trunk 26

and it's operating as a trunk. 27

The encapsulation used is dot1q that how it was configured 28

and that’s how it’s operating. 29

DTP has been disabled. 30

The native VLAN or untagged VLAN on this link is VLAN 1. 31

All VLANs are allowed across the trunk. 32

now we can also use the command show interfaces trunk 33

that shows us a nice summary of information 34

so port 2 and port 3 have been manually configured for trunking using 802.1Q 35

they are currently trunking the native VLAN as VLAN 1. 36

VLANs 1 to 4094 are permitted on those ports 37

the VLANs allowed and active in the management domain are VLANs 1 to 2. 38

VLANs in the Spanning Tree forwarding states on g0/2 is 1 and 2 and on 3 is 2. 39

So we’ve configured switch 1 with this port being access ports. 40

currently, this PC is in VLAN 2 and this PC is in VLAN 1 41

now can router 1 ping router 2 and router 3 42

and can routing 2 ping any of these routers? 43

So can router 1 turn off debugging here, ping 10.1.1.3, yes, it can. 44

Can I ping 10.1.1.4 yes it can. 45

This port allows VLAN 1 to traverse it using the untagged VLAN. 46

so the frame goes across this link as untagged frame 47

goes across this link as untagged frame 48

and then goes across this 2 links as untagged. 49

switch 2 hasn’t been configured for VLANs it's using a default config 50

so sh vlan brief on the switch 51

shows that only VLAN 1 exist on switch 2 52

so let’s put PC 4 into VLAN 2 53

and let’s see if PC 4 and PC 2 can ping each other. 54

Turn off debugging on router 2 acting as our PC 55

sh ip int brief 56

This PC has an IP address of 10.1.2.2 57

So I'll give this one an IP address of 10.1.2.4 58

it’s currently configured with this IP address so let’s change that. 59

10.1.2.4 ping 10.1.2.2 what you’ll notice is the pings failed. 60

Router 2 and router 4 cannot ping each other 61

and the question is why? 62

Why can’t they ping one another? 63

Well the first problem is, we haven’t configured VLAN 2 on this switch 64

switch 2 and we haven’t put this port into VLAN 2. 65

So on switch 2 66

I’m gonna set it to vtp mode transparent 67

so that we have to manually configure everything. 68

I'm gonna create VLAN 2 69

but notice please even though you create the VLAN 70

no ports are put into that VLAN by default. 71

So sh int g0/1 switchport 72

that’s this interface here, shows me that that port is in VLAN 1. 73

So what I need to do is go to that port. 74

switchport mode access to ensure that it's an access port, that is a default. 75

switchport access vlan 2 76

switchport nonegotiate 77

we'll turn off all auto negotiations 78

so that we have to manually configure everything 79

and then explain how it works. 80

So sh int g0/1 switchport 81

This port gigabit 0/1 is enabled 82

which using static access administrative mode 83

and it's operating a static access port, it's in VLAN 2 at the moment. 84

So will PC 2 be able to ping PC 4? 85

let's do the ping again 86

ping fails from router 4 to router 2 87

and it also fails in the reverse direction. 88

These 2 are not able to ping each other. 89

Let’s disable this port and force the traffic to go through the hub 90

and then do a Wireshark capture to see what’s going on.