rewrite (Layer 2 sub-interface view)

Function

The rewrite push command sets a traffic behavior to "push" for packets that an EVC Layer 2 sub-interface receives.

The undo rewrite command deletes a traffic behavior configured on an EVC Layer 2 sub-interface.

The rewrite pop command sets the traffic behavior to "pop" so that an EVC Layer 2 sub-interface removes VLAN tags from received packets.

The undo rewrite command deletes a traffic behavior configured on an EVC Layer 2 sub-interface.

The rewrite swap command sets the traffic behavior to "swap" so that an EVC Layer 2 sub-interface swaps inner and outer VLAN tags in received packets.

The undo rewrite command deletes a traffic behavior configured on an EVC Layer 2 sub-interface.

By default, no traffic behavior is configured on an EVC Layer 2 sub-interface. The EVC Layer 2 sub-interface transparently forwards all received packets without processing them.

Format

rewrite pop { single | double }

rewrite push { vid vid [ ce-vid ce-vid ] }

rewrite push { vid vid 8021p 8021p-value [ ce-vid ce-vid [ ce-8021p ce-8021p-value ] ] }

rewrite push { vid vid 8021p 8021p-value [ ce-vid ce-vid ce-8021p ce-8021p-value ] }

rewrite push { vid vid [ 8021p 8021p-value ] ce-vid ce-vid ce-8021p ce-8021p-value }

rewrite swap

Parameters

Parameter	Description	Value
single	Enables an EVC Layer 2 sub-interface to remove outer tags from single-tagged packets after receiving them.	-
double	Enables an EVC Layer 2 sub-interface to remove double tags from packets after receiving them.	-
push	Push one or more specified VLAN tags.	-
vid vid	Enables an EVC Layer 2 sub-interface to add a tag with a specified VLAN ID to received packets. If an EVC Layer 2 sub-interface receives single-tagged packets, vid vid specifies the VLAN ID in the outer tag to be added to the packets.	The value is an integer ranging from 1 to 4094.
ce-vid ce-vid	Enables an EVC Layer 2 sub-interface to add an inner tag with a specified VLAN ID to received packets.	The value is an integer ranging from 1 to 4094.
8021p 8021p-value	Enables the EVC Layer 2 sub-interface to change 802.1p priorities in received packets to a specified priority value. If an EVC Layer 2 sub-interface receives single-tagged packets, 8021p 8021p-value specifies the 802.1p value in the outer tag to be added to the packets. 802.1p is represented by a 3-bit PRI (priority) field in an 802.1q frame. If traffic is congested on a device, the device forwards frames in descending order by priority values.	The value is an integer ranging from 0 to 7.
ce-8021p ce-8021p-value	Enables the EVC Layer 2 sub-interface to change 802.1p priorities in inner tags of received packets to a specified priority value.	The value is an integer ranging from 0 to 7.
swap	Swap the inner VLAN tag with the outer VLAN tag.	-
pop	Remove one or more specified VLAN tags.	-

Views

400GE Layer 2 sub-interface view, 50GE Layer 2 sub-interface view, Eth-Trunk Layer 2 sub-interface view, GE Layer 2 sub-interface view, Global-VE layer2 subinterface view, VE layer2 subinterface view, Layer 2 sub-interface view

Default Level

2: Configuration level

Task Name and Operations

Task Name	Operations
ethernet	write

Usage Guidelines

Usage Scenario

rewrite pop:

Inter-VLAN communication
VLANs are widely used because they can isolate Layer 2 user packets. Each VLAN logically isolates a broadcast domain from other broadcast domains in a physical LAN. Hosts in each VLAN can communicate with each other, but not hosts in other VLANs. Layer 3 routing techniques must be used to enable inter-VLAN communication.
Traditional Layer 3 Ethernet interfaces consider VLAN-tagged packets invalid and discard them and do not transmit them over routes. To implement inter-VLAN communication, run the interface interface-type interface-number.subnum mode l2 command to create an EVC Layer 2 sub-interface on a Layer 3 Ethernet interface and run the rewrite pop command to set a traffic behavior to pop on the EVC Layer 2 sub-interface. Then the EVC Layer 2 sub-interface can remove VLAN tags after receiving VLAN-tagged packets and implement inter-VLAN communication.
LAN and WAN interconnection
A majority of LAN packets carry VLAN tags, whereas WAN protocols, for example, cannot identify VLAN-tagged packets. In this situation, to forward VLAN-tagged packets from a LAN to a WAN, a device needs to record the VLAN information, remove VLAN tags from packets, and forward them.
rewrite push:
On a metro Ethernet network, user and service packets are identified using VLANs. A 12-bit VLAN tag defined in IEEE 802.1Q identifies a maximum of only 4096 VLANs, which is insufficient for a great number of users in the metro Ethernet. The 802.1Q in 802.1Q (QinQ) technology increases the number of VLAN tags.
The rewrite push command supports the following functions:
Adds one or double tags to each untagged packet.
Adds an outer tag or double tags to each single-tagged packet.
Adds another tag to each double-tagged packet.
rewrite swap:
On Huawei devices, outer tags in QinQ packets identify services, and inner tags must identify users. On some networks, outer tags in QinQ packets identify users, and inner tags identify services. To enable Huawei devices to properly forward QinQ packets to such networks, run the rewrite swap command to swap the inner and outer tags in QinQ packets so that the outer tags identify services, and the inner tags identify users.

Prerequisites

Before run the command rewrite pop,you should check as follows:

1.An EVC Layer 2 sub-interface has been created using the interface interface-type interface-number.subnum mode l2 command in the system view.

2. The EVC Layer 2 sub-interface is not added to a bridge domain. If the EVC Layer 2 sub-interface has been added to a bridge domain, run the undo bridge-domain bd-id command to remove the EVC Layer 2 sub-interface from the bridge domain.

Before run the command rewrite push,you should check as follows:

1.An EVC Layer 2 sub-interface has been created using the interface interface-type interface-number.subnum mode l2 command in the system view.

2.The EVC Layer 2 sub-interface is not added to a bridge domain. If the EVC Layer 2 sub-interface has been added to a bridge domain, run the undo bridge-domain bd-id command to remove the EVC Layer 2 sub-interface from the bridge domain.

Before run the command rewrite swap,you should check as follows:

1.An EVC Layer 2 sub-interface has been created using the interface interface-type interface-number.subnum mode l2 command in the system view.

2.The EVC Layer 2 sub-interface is not added to a bridge domain. If the EVC Layer 2 sub-interface has been added to a bridge domain, run the undo bridge-domain bd-id command to remove the EVC Layer 2 sub-interface from the bridge domain.

3. QinQ encapsulation has been enabled using the encapsulation qinq command in the EVC Layer 2 sub-interface view.

Configuration Impact

After the rewrite pop command is run, a device processes packets as follows:

The device removes tags from received packets before forwarding them at Layer 2. The outbound interface on the device determines whether to tag the forwarded packets.
The device adds VLAN information into packets before forwarding them at Layer 2.

Precautions

A maximum of one traffic behavior can be specified on each EVC Layer 2 sub-interface. If a traffic behavior has been configured on an EVC Layer 2 sub-interface, perform the following operations:

Run the undo rewrite command to delete the existing traffic behavior.
Run the undo bridge-domain command to remove the EVC Layer 2 sub-interface from the existing bridge domain.

Example

# Enable GE 0/1/1.2 to add double tags to packets after receiving them.

<HUAWEI> system-view
[~HUAWEI] interface GigabitEthernet 0/1/1.2 mode l2
[*HUAWEI-GigabitEthernet0/1/1.2] rewrite push vid 20 ce-vid 100 ce-8021p 4

# Enable GE 0/1/1.1 to add a tag to packets after receiving them.

<HUAWEI> system-view
[~HUAWEI] interface GigabitEthernet 0/1/1.1 mode l2
[*HUAWEI-GigabitEthernet0/1/1.1] rewrite push vid 10 8021p 3

# Enable GE 0/1/1.2 to remove single tags from packets after receiving them.

<HUAWEI> system-view
[~HUAWEI] interface GigabitEthernet 0/1/1.2 mode l2
[*HUAWEI-GigabitEthernet0/1/1.2] rewrite pop single

# Enable GE 0/1/1.1 to swap the inner and outer tags in packets after receiving them.

<HUAWEI> system-view
[~HUAWEI] interface GigabitEthernet 0/1/1.1 mode l2
[*HUAWEI-GigabitEthernet0/1/1.1] encapsulation qinq vid 10 ce-vid 100 to 200
[*HUAWEI-GigabitEthernet0/1/1.1] rewrite swap

# Enable GE 0/1/1.1 to remove double tags from packets after receiving them.

<HUAWEI> system-view
[~HUAWEI] interface GigabitEthernet 0/1/1.1 mode l2
[*HUAWEI-GigabitEthernet0/1/1.1] rewrite pop double