Trunk between 2600 and 2950 with IOS

[bpotschien]

Hi there,

I want a dot1q trunk between a 2600 router IOS 12.1 (18) and a 2950 switch IOS 12.1 (22)EA1.

Here is the config of the router:

interface FastEthernet0/0

speed 100

full-duplex

!

interface FastEthernet0/0.1

description to_switch

ip address 1.1.1.1 255.255.255.0

encapsulation dot1Q 1

no ip redirects

and here the switch config:

interface FastEthernet0/24

description Uplink_to_Router

switchport mode trunk

speed 100

duplex full

The VTP status of the switch:

VTP Version : 2

Configuration Revision : 5

Maximum VLANs supported locally : 250

Number of existing VLANs : 5

VTP Operating Mode : Client

VTP Domain Name : STRING

VTP Pruning Mode : Disabled

VTP V2 Mode : Disabled

VTP Traps Generation : Disabled

The trunk does not work! The router does not recieve any trunk packets. The arp cache of the router is "incomplete" related to the switch mac address...

The vlan database on the switch shows the following:

VLAN ISL Id: 1

Name: default

Media Type: Ethernet

VLAN 802.10 Id: 100001

State: Operational

MTU: 1500

Backup CRF Mode: Disabled

Remote SPAN VLAN: No

This is amazing because of the DOT1Q trunk!

Can anyone help?

Thank a lot

[Georg Pauwen]

Hello,

the switch defaults to an ISL trunk. You need to specify that it is a DOT1Q trunk:

interface FastEthernet0/24

description Uplink_to_Router

switchport mode trunk

--> switchport trunk encapsulation dot1q

speed 100

duplex full

HTH,

GP

[thisisshanky]

GP,

I thought 2950's do not support ISL. They do only 802.1q.

Bjoern

What does a "show int fa0/24 switchport" show on the switch. Does it show the trunk status as up ?

[malik.boukraa · Accepted solution]

take a look here: http://www.cisco.com/en/US/tech/tk389/tk390/technologies_configuration_example09186a00800949fd.shtml

In your router your must specify the native vlan used on your switch.

MB

[Kevin Dorrell]

This seems very strange to me. Are you sure it is a 2950-12? It seems to be behaving more like a 2912XL. AFAIK, 2950 does not support ISL because of a hardware limitation - something to do with the ASICs. OTOH, 2912XL did default to ISL.

Kevin Dorrell

Luxembourg

[malik.boukraa]

no it's the normal output of a "show current" in the vlan database. Can we have a "show interface trunk"?

[bpotschien]

Thanks for the answers.

Here is the "sh interfaces fastEthernet 0/24 switchport":

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

Name: Fa0/24

Switchport: Enabled

Administrative Mode: trunk

Operational Mode: trunk

Administrative Trunking Encapsulation: dot1q

Operational Trunking Encapsulation: dot1q

Negotiation of Trunking: On

Access Mode VLAN: 1 (default)

Trunking Native Mode VLAN: 1 (default)

Voice VLAN: none

Administrative private-vlan host-association: none

Administrative private-vlan mapping: none

Administrative private-vlan trunk native VLAN: none

Administrative private-vlan trunk encapsulation: dot1q

Administrative private-vlan trunk normal VLANs: none

Administrative private-vlan trunk private VLANs: none

Operational private-vlan: none

Trunking VLANs Enabled: ALL

Pruning VLANs Enabled: 2-1001

Capture Mode Disabled

Capture VLANs Allowed: ALL

Protected: false

Appliance trust: none

And a "show ver" from the Switch:

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

System returned to ROM by power-on

System image file is "flash:/c2950-i6q4l2-mz.121-22.EA1.bin"

cisco WS-C2950C-24 (RC32300) processor (revision Q0) with 20873K bytes of memory.

Processor board ID FOC0841W3V4

Last reset from system-reset

Running Enhanced Image

26 FastEthernet/IEEE 802.3 interface(s)

And from the router:

Cisco Internetwork Operating System Software

IOS (tm) C2600 Software (C2600-D-M), Version 12.1(18), RELEASE SOFTWARE (fc1)

Copyright (c) 1986-2002 by cisco Systems, Inc.

Compiled Mon 02-Dec-02 23:49 by kellythw

Image text-base: 0x80008088, data-base: 0x80958980

ROM: System Bootstrap, Version 12.2(7r) [cmong 7r], RELEASE SOFTWARE (fc1)

VIERCKT3 uptime is 17 hours, 35 minutes

System returned to ROM by reload

System image file is "flash:c2600-d-mz.121-18.bin"

cisco 2620XM (MPC860) processor (revision 0x100) with 26624K/6144K bytes of memory.

Processor board ID JAD07030RU8 (373713317)

M860 processor: part number 5, mask 2

Channelized E1, Version 1.0.

Bridging software.

X.25 software, Version 3.0.0.

Primary Rate ISDN software, Version 1.1.

Basic Rate ISDN software, Version 1.1.

1 FastEthernet/IEEE 802.3 interface(s)

1 Serial network interface(s)

1 ISDN Basic Rate interface(s)

1 Channelized E1/PRI port(s)

32K bytes of non-volatile configuration memory.

16384K bytes of processor board System flash (Read/Write)

-----------

It is strange that the switch does not have a command to set the enc protocol. The "show interface switchport" shows dot1q, but in "vlan database" it says isl?!?!

Thank you for help

[bpotschien]

An idea:

Do I have to create the vlans on the switch database?

In the moment there are only the vlan 1 and some 100x vlans.

Does the router know that the native vlan is 1? (encap dot1q 1)

[malik.boukraa]

"It is strange that the switch does not have a command to set the enc protocol."

No it's normal since the 2950 only support dot1q for trunking.

[bpotschien]

Well, here is the solution:

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

It is a bug in the IOS version 12.1 (18). The encap dot1q 1 NATIVE is missing in the command stack!

So you have to put the management vlan on the physical interface, not the subinterface.

Correct router config:

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

interface FastEthernet0/0

ip address 1.1.1.1 255.255.255.0

speed 100

full-duplex

!

interface FastEthernet0/0.10

encapsulation dot1Q 10

ip address 10.10.10.1 255.255.255.0

!

interface FastEthernet0/0.20

encapsulation dot1Q 20

ip address 20.20.20.1 255.255.255.0

The correct switch config:

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

interface FastEthernet0/24

description Uplink Router

switchport mode trunk

speed 100

duplex full

Thanks for the help!

Bjoern

[pourvahabi]

hi

i think you have to configure trunk on both side

and also compelete configuration i mean trunk options.

example:

interface fastethernet 0/1

switch mode trunk

switch trunk encap 802.1q

switch port trunk native vlan 10

other side

interf fast ether net 0/24

swtch port mode trunk

switch trunk enca 802.1q

switch port trunk nativ vlan 10

[bpotschien]

Hi,

thanks, but my problem is already resolved.

http://forums.cisco.com/eforum/servlet/NetProf?page=netprof&CommCmd=MB%3Fcmd%3Dpass_through%26location%3Doutline%40%5E1%40%40.1dd70070/7#selected_message