2950/1721 VLAN trunking

[elhughes]

I am having an issue with VLAN trunking between a C2950 and a 1721 router,

If I create a trunk on an etherner port on a 2950, will the 1721 support trunking on its 10/100 interface.

I have configured a trunk on 2950 using

"switchport trunk allowed vlan 102,104"

On the 1721, will creating dot1q subinterfaces for each vlan work.

I have done this- both boxes can see each other by CDP, but we cannot ping.

Apologies for such a simple question, but I have never used 1700's before ( used to 2600 and above)

Thanks in advance.

[pflunkert]

Hi,

what is your native vlan. You should try to configure your native vlan also. When it doesn#t works please post you configs, thanks.

Regards

Peter

[elhughes]

Peter,

Thanks for the reply.

On the 1721 , I have configured the following

interface FastEthernet0

no ip address

speed 100

!

interface FastEthernet0.102

description =Voice vlan=

encapsulation dot1Q 102

ip address x.x.x.x 255.255.255.0

!

interface FastEthernet0.104

description =Data Vlan==

encapsulation dot1Q 104

ip address x.x.x.x 255.255.255.0

On the 2950, I have configured

interface fast 0/1

switchport mode access

switchport trunk allowed vlan 102,104

speed 100

I will try adding the "switchport trunk native vlan x" when I go back to customer site tomorrow.

Many thanks

[milan.kulik]

You should also change your 1721 subinterface config to

encapsulation dot1Q x native

where x means either 102 or 104 depending on VLAN chosen as the native one on your trunk.

And there must be

switchport mode trunk

on your switch port.

Regards,

Milan

[elhughes]

Thanks Milan

[befthimi]

You will probably also need the command"

"switchport mode trunk"

under the 2950 switchport interface.

Have a look at:

http://www.cisco.com/en/US/partner/products/hw/switches/ps628/products_configuration_guide_chapter09186a0080212c3e.html#wp1200245

Bill.

[elhughes]

Bill,

Thanks for the respose.

I'm normally ok with trunking, but I'am a little confused with the 1721 side of things.

The only documentation I can find on 1721 and trunking is using the subinterfaces - but I'm not sure that this is the right way of doing things.

Is this possible on a 1721 with a single 100Mb interface, or is it advisable to use a 26xxXM or add another etherner interface,

Many thanks

Elliot

[milan.kulik]

Read this for detailed understanding:

http://www.cisco.com/warp/customer/473/50.shtml#Tools

Regards,

Milan

[elhughes]

Thanks Milan.

[swpnetwork]

I am also trying to do the same thing on a Cisco 1721. However I am unable to execute the command:-

int fa0.1

encapsulation dot1q 1 native.

^

It does not like dot1q ( or isl )

I have only tried IP Plus software (12.2.15T) and the new 12.3 .11.T IP software but I get the same problem.

IOS stuff says that these support Vlans. However could it be that I need a different feature set. Only have 48M memory so cant try anything greater