why do we have this feature of untagged vlans ? why would we need it, what would we use it for ?

Dear Ankur,

if we connect two routers to single switch and both of router with "native" configuration. It means that there are two trunks, one is router A, other is router B.

Then is it problem in switch because there is only one "VLAN 1" act as native. How to solve it?

Best regards

CM Leung

Hi Leung ,

Suppose if you connect two routers to a single L2 switch u need to place both the trunk links in the same vlan by mentiong as a native vlan.

Create Vlan on L2 switch and place f0/1.1 of both routers in the same vlan by configuring it as encapsulation dot1q 11 native.

L2 config:

vlan 11

ip address 10.105.3.1 255.255.255.0

int f0/1---uplink to first router

switchport trunk native vlan 11

switchport mode trunk

speed 100

duplex full

int f0/2 ---uplink to second router

switchport trunk native vlan 11

switchport mode trunk

speed 100

duplex full

router config:

interface FastEthernet0/0

no ip address

duplex full

speed 100

!

interface FastEthernet0/0.1

encapsulation dot1Q 11 native

ip address 10.105.3.3 255.255.255.0

2'nd router config:

interface FastEthernet0/0

no ip address

duplex full

speed 100

!

interface FastEthernet0/0.1

encapsulation dot1Q 11 native

ip address 10.105.3.5 255.255.255.0

configure the HSRP between those two routers and configure the default gateway on switch which is HSRP IP.

It should work.

Thanks,

Satish

Hi Friend,

If you have 2 routers connected to single switch then you need a trunk or not that depends on your network requirement.

Now suppose you need a trunk then you have to configure 2 ports on single switch as trunk ports , one for each router and you can define native vlan 1 on one trunk and native vlan 2 on other trunk.

Each trunk configuration on single switch is independent of other trunk configuration on same switch.

so for example on switch 1

interface gig1/0/1

switchport trunk encapsulation dot1q

switchport mode trunk

switchport trunk native vlan 1

interface gig1/0/2

switchport trunk encapsulation dot1q

switchport mode trunk

switchport trunk native vlan 2

HTH

Ankur

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Hi Ankur ,

In case of L2 we can configure only one vlan.In that scenario how can we connect or place two routers in different vlans.

I mean we can make routers as L3 by creating subinterfaces on routers.

What could be the default gateway on L2 switch ?

We need to configure default gateway on L2 using ip default gateway command.Am i correct ?

Thanks,

Satish

Hi Satish,

We always configure default gateway on L2 switch for switch reachability through the network.

So when you have one default gateway on your switch which points to router 1 suppose and you can reach your router 1 from anywhere in your network you are good to go.

For all those clients whose default gateway points to router 2 interface ip address will hit router 2 and go out of network and for all those clients whose default gateway points to router 1 will hit router 1 and go out of network.

Default gateway on l2 switch isnot related to data traffic coming out from clients connected to the switch.

May be I understood your question in wrong way so my explaination may not exactly answer your question. Please come again if my explaination does not answer your question.

Regards,

Ankur

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Hi Ankur ,

Thanks for your valuable info...I have small doubt regarding default gateway on L2.

Is there any limitation on no.of default gateway's can be configured on L2.

Thanks,

Satish

Hi Satish,

Yes there is a limitation. You can only have one default gateway configured on your switches. If you already have a default gateway and you try to configure another one it will override the first one.

HTH

Ankur

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Hi Ankur,

Is the limitation only on L2 switches or both L2 and L3 switches. As I have read that a maximum of 3 gateways can be configured on Supervisor Engine on 6500 switch.

Please clarify.

Thanks,

Pavan

Hi Pavan,

It hold true for any switches including Cat6500. You can only have one default-gateway though you can have multiple default routes on L3 switches.

Can you attach the document from where you read the same? Which IOS version is mentioned on that doc?

Regards,

Ankur

Dear Ankur,

Please go through this

http://www.cisco.com/en/US/products/hw/switches/ps700/products_configuration_guide_chapter09186a008007fa1f.html#33089

Best Regards,

Pavan

Hi Pavan,

That's the behavior of CATOS and its not exactly same as default gateway behavior in IOS its basically setting a static route where you have to specify destination network also (you can configure default also) but in IOS default gateway you have no option to set a destination network.

HTH

Ankur

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Hi Ankur,

The purpose of reachability of the switch is served by the vlan interface with an IP address assigned to it. Does default gateway serves the same purpose or does it has other fuction to do?

Thanks,

Pavan