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How to configure a VMAN in EXOS

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TitleHow to configure a VMAN in EXOS
Objective
How to configure a VMAN in EXOS
Environment
  • EXOS
  • Summit
  • BlackDiamond
Procedure
VMANs are typically used in scenarios where a service provider needs to bridge layer 2 services at multiple customer sites.  Generally, the customer needs to transmit multiple VLANs, each with their own VLAN tag, across this service.  In order to support this requirement, and to allow for VLAN ID re-use in the service provider network, a VMAN double tags this traffic with a VMAN ID as it is transmitted across the service provider network.  By default this outer tag has an ethertype of 0x88a8, but this can be changed to other ethertypes as needed.  The double tagged traffic is forwarded through the service provider network just as a VLAN would be, with the exception being that it is identified via the VMAN ID and the inner customer VLAN IDs are ignored.  

VMANs are created similarly to VLANs.  The following commands are used to create and configure a vman:

create vman <VMAN_NAME>
configure vman tag <VMAN_TAG>
configure vman add ports <PORT_LIST> { tagged | untagged }


Jumbo frames must be enabled on VMAN ports (to account for the second tag):

enable jumbo-frame ports <VMAN_PORTS>

Occasionally the ethertype may need to be changed in order for VMAN traffic to be forwarded across non-Extreme devices:

configure vman ethertype <ETHERTYPE>

Consider the following example topology:

Example VMAN Topology

Provider Edge A & B Configurations
create vman SP
configure vman tag 100
configure vman sp add port 2 tagged
configure vman sp add port 1 untagged
enable jumbo-frame ports 1,2

Note: Port 1 is added to the VMAN untagged.  It is the port connected to the customer site and is the ingress port for the VMAN.  All traffic that ingresses this port will be encapsulated into the VMAN and forwarded across the service provider network via VMAN ID 100.  Untagged VMAN ports can be thought of as "edge" ports to the VMAN service.  Port 2 is added tagged as it is a switch interconnect within the service provider network.  All traffic that egresses port 2 will be double tagged with the customer VLAN ID as well as an out VMAN tag of 100.

Customer Edge 1 & 2 Configurations
create vlan green tag 10
create vlan purple tag 20
create vlan orange tag 30
configure vlan green add port 1 tagged
configure vlan purple add port 1 tagged
configure vlan orange add port 1 tagged

Note: There are no VMANs created on the customer switch.  The service provider network connected on port 1 of this switch would be transparent to the customer.  From the customer switch perspective it would seem as if it was directly connected to the other customer site(s)
Additional notes
For an example of this procedure in EOS, see the below link:
How to configure "Provider-Bridge" (Q-in-Q) on a S-Series

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