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VLANs and VPLS Routing Instances

 

Guidelines for Configuring VLAN Identifiers for VLANs and VPLS Routing Instances

For a VLAN that is performing Layer 2 switching only, you do not have to specify a VLAN identifier.

For a VLAN that is performing Layer 3 IP routing, you must specify either a VLAN identifier or dual VLAN identifier tags.

For a VPLS routing instance, you must specify either a VLAN identifier or dual VLAN identifier tags.

Configuring VLAN Identifiers for VLANs and VPLS Routing Instances

You can configure VLAN identifiers for a VLAN or a VPLS routing instance in the following ways:

  • By using either the vlan-id statement or the vlan-tags statement to configure a normalizing VLAN identifier. This topic describes how normalizing VLAN identifiers are processed and translated in a VLAN or a VPLS routing instance.

  • By using the input-vlan-map and the output-vlan-map statements at the [edit interfaces interface-name unit logic-unit-number] or [edit logical-systems logical-system-name interfaces interface-name unit logic-unit-number] hierarchy level to configure VLAN mapping.

The vlan-id and vlan-tags statements are used to specify the normalizing VLAN identifier under the VLAN or VPLS routing instance. The normalizing VLAN identifier is used to perform the following functions:

  • Translate, or normalize, the VLAN tags of packets received into a learn VLAN identifier.

  • Create multiple learning domains that each contain a learn VLAN identifier. A learning domain is a MAC address database to which MAC addresses are added based on the learn VLAN identifier.

Note

You cannot configure VLAN mapping using the input-vlan-map and output-vlan-map statements if you configure a normalizing VLAN identifier for a VLAN or VPLS routing instance using the vlan-id or vlan-tags statements.

To configure a VLAN identifier for a VLAN, include either the vlan-id or the vlan-tags statement at the [edit interfaces interface-name unit logic-unit-number] or [edit logical-systems logical-system-name interfaces interface-name unit logic-unit-number] hierarchy level, and then include that logical interface in the VLAN configuration.

For a VPLS routing instance, include either the vlan-id or vlan-tags statement at the [edit interfaces interface-name unit logic-unit-number] or [edit logical-systems logical-system-name interfaces interface-name unit logic-unit-number] hierarchy level, and then include that logical interface in the VPLS routing instance configuration.

Note

ACX Series routers do not support the [edit logical-systems] hierarchy.

Note

For a single VLAN or VPLS routing instance, you can include either the vlan-id or the vlan-tags statement, but not both. If you do not configure a vlan-id, vlan-tags, or vlan-id-list [ vlan-id-numbers ] for the VLAN or the VPLS routing instance, the Layer 2 packets received are forwarded to the outbound Layer 2 interface without having the VLAN tag modified unless an output-vlan-map is configured on the Layer 2 interface. This results in a frame being forwarded to a Layer 2 interface with a VLAN tag that is different from what is configured for the Layer 2 interface. Note that a frame received from the Layer 2 interface is still required to match the VLAN tag(s) specified in the interface configuration. The invalid configuration may cause a Layer 2 loop to occur.

The VLAN tags associated with the inbound logical interface are compared with the normalizing VLAN identifier. If the tags are different, they are rewritten as described in Table 1. The source MAC address of a received packet is learned based on the normalizing VLAN identifier.

Note

You do not have to specify a VLAN identifier for a VLAN that is performing Layer 2 switching only. To support Layer 3 IP routing, you must specify either a VLAN identifier or a pair of VLAN tags. However, you cannot specify the same VLAN identifier for more than one VLAN within a routing instance. Each VLAN must have a unique VLAN identifier.

If the VLAN tags associated with the outbound logical interface and the normalizing VLAN identifier are different, the normalizing VLAN identifier is rewritten to match the VLAN tags of the outbound logical interface, as described in Table 2.

For the packets sent over the VPLS routing instance to be tagged by the normalizing VLAN identifier, include one of the following configuration statements:

  • vlan-id number to tag all packets that are sent over the VPLS virtual tunnel (VT) interfaces with the VLAN identifier.

  • vlan-tags outer number inner number to tag all packets sent over the VPLS VT interfaces with dual outer and inner VLAN tags.

Use the vlan-id none statement to have the VLAN tags removed from packets associated with an inbound logical interface when those packets are sent over VPLS VT interfaces. Note that those packets might still be sent with other customer VLAN tags.

The vlan-id all statement enables you to configure bridging for several VLANs with a minimum amount of configuration. Configuring this statement creates a learning domain for:

  • Each inner VLAN, or learn VLAN, identifier of a logical interface configured with two VLAN tags

  • Each VLAN, or learn VLAN, identifier of a logical interface configured with one VLAN tag

We recommend that you do not use customer VLAN IDs in a VPLS routing instance because customer VLAN IDs are used for learning only.

You should use the service VLAN ID in a VPLS routing instance, as in the following configuration:

Note

If you configure the vlan-id all statement in a VPLS routing instance, we recommend using the input-vlan-map pop and output-vlan-map push statements on the logical interface to pop the service VLAN ID on input and push the service VLAN ID on output and in this way, limit the impact of double-tagged frames on scaling. You cannot use the native vlan- id statement when the vlan-id all statement is included in the configuration.

The vlan-id-list [ vlan-id-numbers ] statement enables you to configure bridging for multiple VLANs on a trunk interface. Configuring this statement creates a learning domain for:

  • Each VLAN listed: vlan-id-list [ 100 200 300 ]

  • Each VLAN in a range: vlan-id-list [ 100-200 ]

  • Each VLAN in a list and range combination: vlan-id-list [ 50, 100-200, 300 ]

The following steps outline the process for bridging a packet received over a Layer 2 logical interface when you specify a normalizing VLAN identifier using either the vlan-id number or vlan-tags statement for a VLAN or a VPLS routing instance:

  1. When a packet is received on a physical port, it is accepted only if the VLAN identifier of the packet matches the VLAN identifier of one of the logical interfaces configured on that port.
  2. The VLAN tags of the received packet are then compared with the normalizing VLAN identifier. If the VLAN tags of the packet are different from the normalizing VLAN identifier, the VLAN tags are rewritten as described in Table 1.
  3. If the source MAC address of the received packet is not present in the source MAC table, it is learned based on the normalizing VLAN identifier.
  4. The packet is then forwarded toward one or more outbound Layer 2 logical interfaces based on the destination MAC address. A packet with a known unicast destination MAC address is forwarded only to one outbound logical interface. For each outbound Layer 2 logical interface, the normalizing VLAN identifier configured for the VLAN or VPLS routing instance is compared with the VLAN tags configured on that logical interface. If the VLAN tags associated with an outbound logical interface do not match the normalizing VLAN identifier configured for the VLAN or VPLS routing instance, the VLAN tags are rewritten as described in Table 2.

The tables below show how VLAN tags are applied for traffic sent to and from the VLAN, depending on how the vlan-id and vlan-tags statements are configured for the VLAN and on how identifiers are configured for the logical interfaces in a VLAN or VPLS routing instance. Depending on your configuration, the following rewrite operations are performed on VLAN tags:

  • pop—Remove a VLAN tag from the top of the VLAN tag stack.

  • pop-pop—Remove both the outer and inner VLAN tags of the frame.

  • pop-swap—Remove the outer VLAN tag of the frame and replace the inner VLAN tag of the frame.

  • swap—Replace the VLAN tag of the frame.

  • push—Add a new VLAN tag to the top of the VLAN stack.

  • push-push—Push two VLAN tags in front of the frame.

  • swap-push—Replace the VLAN tag of the frame and add a new VLAN tag to the top of the VLAN stack.

  • swap-swap—Replace both the outer and inner VLAN tags of the frame.

Table 1 shows specific examples of how the VLAN tags for packets sent to the VLAN are processed and translated, depending on your configuration. “–” means that the statement is not supported for the specified logical interface VLAN identifier. “No operation” means that the VLAN tags of the received packet are not translated for the specified input logical interface.

Table 1: Statement Usage and Input Rewrite Operations for VLAN Identifiers for a VLAN

VLAN Identifier of

Logical Interface

VLAN Configurations for a VLAN

vlan-id none

vlan-id 200

vlan-id all

vlan tags outer 100

inner 300

none

No operation

push 200

push 100, push 300

200

pop 200

No operation

No operation

swap 200 to 300,

push 100

1000

pop 1000

swap 1000 to 200

No operation

swap 1000 to 300,

push 100

vlan-tags outer 2000

inner 300

pop 2000, pop 300

pop 2000, swap 300

to 200

pop 2000

swap 2000 to 100

vlan-tags outer 100

inner 400

pop 100, pop 400

pop 100, swap 400

to 200

pop 100

swap 400 to 300

vlan-id-range 10-100

No operation

vlan-tags outer 200 inner-range 10-100

pop 200

Table 2 shows specific examples of how the VLAN tags for packets sent from the VLAN are processed and translated, depending on your configuration. “–” means that the statement is not supported for the specified logical interface VLAN identifier. “No operation” means that the VLAN tags of the outbound packet are not translated for the specified output logical interface.

Table 2: Statement Usage and Output Rewrite Operations for VLAN Identifiers for a VLAN

VLAN Identifier of

Logical Interface

VLAN Configurations for a VLAN

vlan-id none

vlan-id 200

vlan-id all

vlan tags outer 100

inner 300

none

no operation

pop 200

pop 100, pop 300

200

push 200

No operation

No operation

pop 100, swap 300

to 200

1000

push 1000

swap 200 to 1000

No operation

pop 100, swap 300

to 1000

vlan-tags outer 2000

inner 300

push 2000, push 300

swap 200 to 300,

push 2000

push 2000

swap 100 to 2000

vlan-tags outer 100 inner 400

push 100, push 400

swap 200 to 400,

push 100

push 100

swap 300 to 400

vlan-id-range 10-100

No operation

vlan-tags outer 200 inner-range 10-100

push 200