Ccna routing and Switching Complete Study Guide

sh interfaces trunk

 

S2>

sh interfaces trunk

 

Not a scrap of output—that’s definitely a bad sign! Let’s take another look at the 

show 

vlan

 output on S1 and see what we can find out:

S1>

sh vlan brief

 

---

868

 

Chapter 20 

■

  Troubleshooting IP, IPv6, and VLANs

VLAN Name                             Status    Ports

---- -------------------------------- --------- -------------------------------

1    default                          active    Gi0/3, Gi0/4, Gi0/5, Gi0/6

                                                Gi0/7, Gi0/8, Gi0/9, Gi0/10

                                                Gi0/11, Gi0/12, Gi0/13, Gi0/14

                                                Gi0/15, Gi0/16, Gi0/17, Gi0/18

                                                Gi0/19, Gi0/20, Gi0/21, Gi0/22

                                                Gi0/23, Gi0/24, Gi0/25, Gi0/26

                                                Gi0/27, Gi0/28

10   Sales                            active    Gi0/1, Gi0/2

20   Accounting                       active

[output cut]

Nothing new from when we checked it a few minutes ago, but look there under VLAN 

1—we can see interfaces Gi0/13 and Gi0/14. This means that our ports between switches 

are members of VLAN 1 and will pass only VLAN 1 frames!

Typically I’ll tell my students that if you type the 

show vlan

 command, you’re really 

typing the nonexistent “show access ports” command since this output shows interfaces 

in access mode but doesn’t show the trunk interfaces. This means that our ports between 

switches are access ports instead of trunk ports, so they’ll pass information about only 

VLAN 1.

Let’s go back over to the S2 switch to verify and see which port interfaces Gi0/13 and 

Gi0/14 are members of:

S2>

sh vlan brief

 

VLAN Name                             Status    Ports

---- -------------------------------- --------- -----------------------------

1    default                          active    Gi0/1, Gi0/2, Gi0/4, Gi0/5

                                                Gi0/6, Gi0/7, Gi0/8, Gi0/9

                                                Gi0/10, Gi0/11, Gi0/12, Gi0/13

                                                Gi0/14, Gi0/15, Gi0/16, Gi0/17

                                                Gi0/18, Gi0/19, Gi0/20, Gi0/21

                                                Gi0/22, Gi0/23, Gi0/24, Gi0/25

                                                Gi0/26, Gi0/27, Gi0/28

10   Sales                            active    Gi0/3

Again, as with S1, the links between switches are showing in the output of the 

show vlan

 command, which means that they are not trunk ports. We can use the 

show 

interfaces 

interface switchport

 command to verify this as well:

S1#