VLAN trunking issues

[gibson89lx]

I have a setup where I have 2 2900XL(a 12 port and a 24 port) switches connected via VTP trunking and from 1 switch to a 2621 router via ISL encapsulation. I have the interface on the router divided into .1, .2, and .3 sub interfaces with the encapsulation set as ISL.

The 24 port has 2 VLANs configured on it and the 12 port has one. I have yet to succeed in pinging out. I know it must be something really stupid that I missed but I can't figure out what. Can someone assist me by possibly posting a step by step instruction sheet, or possibly a checklist that I could refer to?

Thanks in Advance,

Matt

[Prashanth Krishnappa]

Post your configurations or see if you have configured it per the following tech tip

http://www.cisco.com/warp/public/473/50.shtml

[aashish.c]

Hi,

Whichever switch is connected to router, that should have the vlan created in its database of the previous switch. For example

sw1-------sw2------router

Any vlan(s) which is created on sw1, those vlan(s) should also be created in sw2`s vlan database

the command to check vlan database is :

sw#sh vlan

and the link between sw1 and sw2 should be a trunk link and the required vlans should be allowed on that link as well as between sw2 and router.

kindly update

regards

Aashish C

[gibson89lx]

correct, I think what my problem is I can't get the trunk port on sw2 to allow BOTH VLANs to pass through, it seems I can only get one to pass through.

[aashish.c]

hi,

just check, incase you have sw2 which is 2900xl has only 4mb flash. Then unfortunately it will not support trunking. you can`t make a trunk port on 4mb 2900xl switch.

If above is not the case, then by default whenever you make a trunk port all the vlans are allowed through it. here are the comamnds to create a trunk port

sw(config-if)#switchport trunk encap dot1q

sw(config-if)#switchport mode trunk

kindly update for further clarification.

regards

aashish C

[gibson89lx]

No, it has more than 4mb of flash so I'm ok there. When you've got 2 trunk lines(1 line between the switches and 1 line between the switch and router) Do you make the trunks a member of the VLAN? I guess what I'm asing is for example

SW1

f0/1(Trunk from SW1 to SW2)

f0/2-f0/24(VLAN #101)

SW2

f0/1(trunk from SW1 to SW2)

f0/2(trunk from SW2 to 2621 router f0/1)

f0/3-f0/12(VLAN #102)

What would be the membership of f0/1 on sw1, f0/1 on sw2, and f0/2 on sw3? How does that work with membership because I was always taught that even though it's a trunk it belongs to a VLAN, I always took that with a grain of salt but *shrug*

So essentially I've only got 2 VLANs 1 on 1 switch and 1 on the other and I need them to both talk to a server which is on the f0/0 interface on my router. The VLANs can talk between each other or they can be seperate it doesn't really matter. Also how do VLANs work with DHCP broadcasts? I would think they would be contained correct?

I'm sorry I'm asking so many questions but I'm work-study and still in school. Thanks for your time.

[network_guy11]

Try changing the encapsulation on your router to dot1q

on subinterface issue the commands

encapsulation dot1q VLANNO( 2,3 etc)

[gibson89lx]

here's my sh runs.

Building configuration...

Current configuration : 845 bytes

!

version 12.3

service timestamps debug datetime msec

service timestamps log datetime msec

no service password-encryption

!

hostname Router

!

!

ip subnet-zero

!

!

!

!

!

!

!

interface FastEthernet0/0

ip address 172.16.2.1 255.255.255.0

duplex auto

speed auto

!

interface Serial0/0

no ip address

shutdown

!

interface FastEthernet0/1

no ip address

duplex auto

speed auto

!

interface FastEthernet0/1.1

encapsulation isl 101

ip address 172.16.0.1 255.255.255.0

no ip redirects

!

interface FastEthernet0/1.2

encapsulation isl 102

ip address 172.16.1.1 255.255.255.0

no ip redirects

!

interface Serial0/1

no ip address

shutdown

!

router eigrp 101

network 172.16.0.0 0.0.0.255

network 172.16.1.0 0.0.0.255

network 172.16.2.0 0.0.0.255

auto-summary

!

no ip http server

ip classless

!

!

!

line con 0

line aux 0

line vty 0 4

!

!

!

end

-------------------------switch1------------------------

Building configuration...

Current configuration:

!

version 12.0

no service pad

service timestamps debug uptime

service timestamps log uptime

no service password-encryption

!

hostname Switch

!

!

!

!

!

!

!

ip subnet-zero

!

!

!

interface FastEthernet0/1

switchport trunk encapsulation dot1q

switchport mode trunk

!

interface FastEthernet0/2

switchport access vlan 101

!

interface FastEthernet0/3

switchport access vlan 101

!

interface FastEthernet0/4

switchport access vlan 101

!

interface FastEthernet0/5

switchport access vlan 101

!

interface FastEthernet0/6

switchport access vlan 101

!

interface FastEthernet0/7

switchport access vlan 101

!

interface FastEthernet0/8

switchport access vlan 101

!

interface FastEthernet0/9

switchport access vlan 101

!

interface FastEthernet0/10

switchport access vlan 101

!

interface FastEthernet0/11

switchport access vlan 101

!

interface FastEthernet0/12

switchport access vlan 101

!

interface FastEthernet0/13

switchport access vlan 101

!

interface FastEthernet0/14

switchport access vlan 101

!

interface FastEthernet0/15

switchport access vlan 101

!

interface FastEthernet0/16

switchport access vlan 101

!

interface FastEthernet0/17

switchport access vlan 101

!

interface FastEthernet0/18

switchport access vlan 101

!

interface FastEthernet0/19

switchport access vlan 101

!

interface FastEthernet0/20

switchport access vlan 101

!

!

switchport access vlan 101

!

interface FastEthernet0/22

switchport access vlan 101

!

interface FastEthernet0/23

switchport access vlan 101

!

interface FastEthernet0/24

switchport access vlan 101

!

interface VLAN1

no ip directed-broadcast

no ip route-cache

!

!

line con 0

transport input none

stopbits 1

line vty 5 15

!

end

-----------------------switch2-----------------------------

Building configuration...

Current configuration:

!

version 12.0

no service pad

service timestamps debug uptime

service timestamps log uptime

no service password-encryption

!

hostname Switch

!

!

!

!

!

!

!

ip subnet-zero

!

!

!

interface FastEthernet0/1

switchport trunk encapsulation dot1q

switchport mode trunk

!

interface FastEthernet0/2

switchport access vlan 102

switchport mode trunk

!

interface FastEthernet0/3

switchport access vlan 102

!

interface FastEthernet0/4

switchport access vlan 102

!

interface FastEthernet0/5

switchport access vlan 102

!

interface FastEthernet0/6

switchport access vlan 102

!

interface FastEthernet0/7

switchport access vlan 102

!

interface FastEthernet0/8

switchport access vlan 102

!

interface FastEthernet0/9

switchport access vlan 102

!

interface FastEthernet0/10

switchport access vlan 102

!

interface FastEthernet0/11

switchport access vlan 102

!

interface FastEthernet0/12

switchport access vlan 102

!

interface VLAN1

no ip directed-broadcast

no ip route-cache

!

!

line con 0

transport input none

stopbits 1

line vty 5 15

!

end

[hnorvik]

Matt,

Looking at your config I would say I would agree with network_guy. Change your encapsulation on 2621 to use dot1q.

In addition, correctly set the fa0/2 if on sw2 to dot1q encapsulation (you are now using the default) and no switchport access....

I would also suggest that you add another sub-interface on 2621 for VLAN 1. Add IP-addresses for VLAN 1 on SW1 and SW2 (unless you already have it and don't want to disclose them). You can then ping from each switch to test connectivity. Try ping from the 2621 and work your way towards your sw1.

Harald.

[gibson89lx]

configure VLAN1 even though it's not being used?

Also, I was told that in order to talk across routers you HAD to use ISL instead of dot1q. Was the person telling me this mistaken?

[hnorvik]

VLAN 1: You add an IP address to your switch to make it possible to telnet to it. If not you'd have to use the console port to access it. By default, this sets up VLAN1 as the management VLAN. It's just for the ease of troubleshooting I would add IP addresses to your VLAN 1 interfaces on sw1 and sw2, and add another subinterface on the router for the same VLAN. All addresses has to be in the same subnet.

ISL or not DOT1Q on routers: I don't know where you've heard that? Maybe some older IOS version/HW since they only supported ISL and not dot1q (like the 4MB 2900xl switches). As far as I remember you were running a pretty recent IOS on your router.

Anyway, I would recommend running only one type of trunking, dot1q or ISL in your network.

Check also your trunk port setting on sw1 and sw2 by using the command show int switchport.

harald

[griffijo]

Just to clarify, you can't run dot1q or isl on 4mb 2900; you can't trunk at all.

[gibson89lx]

Wait, all of the addresses have to be on the same subnet? When I configure the subinterfaces on the router unless they're different networks it gives me the overlapping error. I'm running the 172.16.*.* through a /24 mask not a /16 mask. What I essentially need is 50 addresses for one subnet and 200 for another. the 200 subnet is on sw2 which is a 12 port that has 4 lines that go to unmanaged switches in other rooms. sw1 is going to be upgraded later to a 48 port and is going to have a direct line from each port to a computer. The top switch needs it's own VLAN as the bottom switch VLAN 101 and 102 respectivly. I thought I could take a 172.16.0.* and divide the last octet into 200 for vlan1 and 50 for vlan2 but when I went to configure the f0/1 on the router I had to make each sub-if a different network.

I thought I had this all figured out but now I'm somewhat confused. I've followed everything in my books and from resources online but none of it seems to work.

Also, I know about the 4mb 2900s the ones I'm working with are 8mb as I recall

[hnorvik]

Sorry for the confusion.

On your router, each VLAN has it's own subnet. If you have 50 + 200 nodes in each vlan, two class C subnets will do - like you've already did according to your config.

What I really meant was that if you use a management network on the same VLAN, all IP-addresses has to be in the same subnet.

To debug your current setup, you have to test from the router to a PC connected to one port on either sw1 or sw2. Ping from your router, and check the arp table on your router if the IP address gets resolved. If it doesn't, you don't have layer 3 connectivity between the PC and the router (and maybe not layer2 connectivity).

I find this setup has too many variables to troubleshoot, so just to make the testing easier, forget about Vlan1. To add an IP-address for management in each of sw1 and sw2, add Interface VLAN101 on sw1 with ip address 172.16.0.254/24 and interface VLAN102 on sw2 with ip address 172.16.1.254/24. Make sure you do a no shutdown on both interfaces. Try to ping these addresses from your router, check the arp table if it doesn't work.

What's the result of your show int fa0/1 switchport on sw1 and sw2, and show int fa0/2 switchport on sw2?

Do a "show cdp neighbors" on sw2 to verify that both sw1 and 2621 show up. That means that they talk together on vlan1.

And your switches must be 8MB switches. If not, you couldn't run version 12.

Harald.

[gibson89lx]

I FINALLY fixed it! It was a stupid stupid gateway problem on the computers themselves. The DHCP server wasn't giving it out with the IP leases DUH, I feel stupid now. Thanks for all the help guys!