11-7
Cisco ME 3800X and 3600X Switch Software Configuration Guide
OL-23400-01
Chapter 11 Configuring Ethernet Virtual Connections (EVCs)
Understanding EVC Features
Rewrite Operations
You can use the rewrite command to modify packet VLAN tags. You can use this command to emulate
traditional 802.1Q tagging, where packets enter a switch on the native VLAN and VLAN tagging
properties are added on egress. You can also use the rewrite command to facilitate VLAN translation
and QinQ.
Enter the rewrite ingress tag pop {1 | 2} symmetric service-instance configuration mode command to
specify the encapsulation adjustment to be performed on the frame ingress to the EFP. Entering pop 1
pops (removes) the outermost tag; entering pop 2 removes two outermost tags.
Note
The symmetric keyword is required to complete rewrite to configuration.
When you enter the symmetric keyword, the egress counterpart performs the inverse action and pushes
(adds) the encapsulation VLAN. You can use the symmetric keyword only with ingress rewrites and
only when single VLANs are configured in encapsulation. If you configure a list of VLANs or a VLAN
range or encapsulation default or encapsulation any, the symmetric keyword is not accepted for
rewrite operations.
The ME 3800X and ME 3600X switches support only these rewrite commands.
rewrite ingress tag pop 1 symmetric
rewrite ingress tag pop 2 symmetric
The switch does not support rewrite commands for ingress push and translate in this release. However,
you can use the rewrite ingress tag pop symmetric command to achieve translation. Possible
translation combinations are 1-to-1, 1-to-2, 2-to-1, and 2-to-2. When forwarding to or from a Layer 2
port, you cannot achieve 2-to2 translation because a Layer 2 port is implicitly defined to be rewrite
ingress tag pop 1 symmetric.
The switch does not support egress rewrite operations beyond the second VLAN that a packet carries
into a switch. Because of the egress rewrite limitation, if an EFP has a pop 2 rewrite operation at ingress,
no other EFP in the same bridge domain can have a rewrite operation. See the
“Global Rewrite Operation
Limitation on a Switch” section on page 11-14
.
Table 11-2
Maximum Allowed Service Instance Configuration with and without Split Horizons
Configured in
Bridge Domain
Maximum Service Instances in the Group
Total Service
Instances in
Bridge Domain
No group
Group 0
Group 1
Group 2
No Group
64
–
–
–
64
Split Group 0
32
32
–
–
64
Split Group 1
16
16
16
-
48
Split Group 2
16
16
16
16
64
