Dot1Q Tunneling for Etherchannels

Answered Question
May 15th, 2009

Hi All,

I'm reading about Dot1Q Tunneling on Cisco Doco (http://cisco.com/en/US/docs/switches/lan/catalyst3750e_3560e/software/release/12.2_50_se/configuration/guide/swtunnel.html#wp1018452). One thing that I cannot find explanation, why on the SP sides we need to create several access vlans? Can we just create one access vlan and create an etherchannel for it?

Regards,

David Sudjiman

Correct Answer by Giuseppe Larosa about 7 years 9 months ago

Hello David,

802.1Q tunneling works well to emulate a point to point link between customer switches ports.

In order for the L2 SP to support a customer side etherchannel one customer vlan for each member link is needed.

In other words you cannot combine etherchannel and 802.1Q tunneling on the service provider switch ports.

Using a single customer vlan would cause frames from link #1 to arrive on link#2 causing a terrible mess and also there is potential for broadcast storms.

By using different customer vlans all ambiguities are eliminated ad frames from link1 are sent only to link1 on the other site.

So etherchannels are supported as a set of point-to-point links.

Hope to help

Giuseppe

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Correct Answer
Giuseppe Larosa Sat, 05/16/2009 - 11:01

Hello David,

802.1Q tunneling works well to emulate a point to point link between customer switches ports.

In order for the L2 SP to support a customer side etherchannel one customer vlan for each member link is needed.

In other words you cannot combine etherchannel and 802.1Q tunneling on the service provider switch ports.

Using a single customer vlan would cause frames from link #1 to arrive on link#2 causing a terrible mess and also there is potential for broadcast storms.

By using different customer vlans all ambiguities are eliminated ad frames from link1 are sent only to link1 on the other site.

So etherchannels are supported as a set of point-to-point links.

Hope to help

Giuseppe

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