Spanning tree on Native VLAN

Answered Question
Mar 23rd, 2009
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Hi All,


I'm drawing a blank with spanning tree at the moment.


All ports would be configured as trunks. I have access switches downstream from L3_SW_01 and L3_SW_02 which are trunked rather than routed. With respect to the attached diagram, would I be creating a loop for the native VLAN 1?


I would like to use HSRP on the LAN and DMZ interfaces of the Edge routers for redundancy which is why I proposed the use of sub-interfaces.


Can the native vlan be specified per trunk, or is it global to the switch/router?


Would routed connections between the L3_Switches and Edge routers be more appropriate?


Any comments or suggestions would be welcome.


Thanks


Kevin




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Correct Answer by Giuseppe Larosa about 8 years 3 days ago

Hello Kevin,

native VLan concept applies to 802.1Q trunks only.

the default native vlan is 1 for all trunks.

This configuration can be overriden on a per link basis with


switchport trunk native vlan xx


both ends of a single link have to agree on the native vlan identity.


STP BPDus for the native Vlan are sent by PVST as original 802.1D STP frames all other STP per vlan instances use the Cisco proprietary format.


see this very useful best practice


http://www.cisco.com/en/US/products/hw/switches/ps700/products_white_paper09186a00801b49a4.shtml



about links between L3_switches and edge routers:

you can think of using L3 routed links as a way to provide more security.


Hope to help

Giuseppe


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Correct Answer
Giuseppe Larosa Mon, 03/23/2009 - 09:35
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Hello Kevin,

native VLan concept applies to 802.1Q trunks only.

the default native vlan is 1 for all trunks.

This configuration can be overriden on a per link basis with


switchport trunk native vlan xx


both ends of a single link have to agree on the native vlan identity.


STP BPDus for the native Vlan are sent by PVST as original 802.1D STP frames all other STP per vlan instances use the Cisco proprietary format.


see this very useful best practice


http://www.cisco.com/en/US/products/hw/switches/ps700/products_white_paper09186a00801b49a4.shtml



about links between L3_switches and edge routers:

you can think of using L3 routed links as a way to provide more security.


Hope to help

Giuseppe


Kevin Brennan Mon, 03/23/2009 - 10:39
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Hi Giuseppe,


Thank you for that.


If I were to opt for a routed link between L3_Switches and edge, would I simply use two equaly weighted static routes instead of HSRP?


Thanks


Kevin

Giuseppe Larosa Mon, 03/23/2009 - 11:58
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Hello Kevin,

I would consider the usage of a dynamic routing protocol but with point-to-point routed links static routes can be used too.


Hope to help

Giuseppe


Kevin Brennan Tue, 03/24/2009 - 02:56
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Hi Giuseppe,


Thank you for your help.


Kevin

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