L2PT multicast mac address

I have a question about L2PT, especially from this documentation:

http://www.Cisco.com/en/us/docs/switches/LAN/catalyst3550/software/release/12.2_25_seb/configuration/guide/swtunnel.html#wp1005050

To my knowledge, when switch PE l2pt receive a bpdu, it will replace the destination MAC address by owner of Cisco (01-00-0c-cd-cd-d0) multicast address. This MAC address will be used until the BPDU packet reaches the output PE.

According to the Cisco documentation:

The edge lights up catering out side the appropriate layer 2 Protocol and the MAC address and transfer the packets to all ports of tunnel or access on the subway even VLAN. Therefore, the layer 2 PDU remain intact and are sent over the network from the other side of the client network service provider.


... When packets double marking enter switch D, the tag VLAN 40 metro is removed. The MAC address is replaced by the Protocol Layer 2 respective MAC address and the packet is sent to the customer Y Site 2 as a single frame in VLAN 100.

If I get it correctly, then it means that the MAC address of the destination output switch returned to the original BPDU MAC address (for example the CDP multicast address). My question is, if the destination MAc was crushed, how know MAC address of origin output switch?

Second question: is the address 01-00-0c-cd-cd-d0 MAC used for all protocols BPDU tunnel? Or is there another MAC destination for each Protocol (01-00-0c-cd-cd-d0 CDP, something else for STP, etc.). If it's the same thing how the output switch knows what protocol the BPDU belongs to?

Thanks in advance.

Hello Sultan,

note

> If the destination MAc was crushed, how does the output switch know the original MAC address?

a protocol in the frame type field allows to rebuild the right destination, MAC address, most of these frameworks use LLC/SNAP encapsulation and it is not deleted.

See

LAN password best practices IOS, it contains a table with all types of Protocol CDP, DTP, VTP and so on

http://www.Cisco.com/en/us/products/hw/switches/PS700/products_white_paper09186a00801b49a4.shtml

Hope to help

Giuseppe

Tags: Cisco Support

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