Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?

 
ON THIS PAGE
 

Troubleshooting an Unexpected Rewrite Value

Problem

Description

Traffic from one or more forwarding classes on an egress port is assigned an unexpected rewrite value.

Note:

For packets that carry both an inner VLAN tag and an outer VLAN tag, the rewrite rules rewrite only the outer VLAN tag.

Cause

If you configure a rewrite rule for a forwarding class on an egress port, but you do not configure a rewrite rule for every forwarding class on that egress port, then the forwarding classes that do not have a configured rewrite rule are assigned random rewrite values.

For example:

  1. Configure forwarding classes fc1, fc2, and fc3.

  2. Configure rewrite rules for forwarding classes fc1 and fc2, but not for forwarding class fc3.

  3. Assign forwarding classes fc1, fc2, and fc3 to a port.

When traffic for these forwarding classes flows through the port, traffic for forwarding classes fc1 and fc2 is rewritten correctly. However, traffic for forwarding class fc3 is assigned a random rewrite value.

Solution

If any forwarding class on an egress port has a configured rewrite rule, then all forwarding classes on that egress port must have a configured rewrite rule. Configuring a rewrite rule for any forwarding class that is assigned a random rewrite value solves the problem.

Tip:

If you want the forwarding class to use the same code point value assigned to it by the ingress classifier, specify that value as the rewrite rule value. For example, if a forwarding class has the IEEE 802.1 ingress classifier code point value 011, configure a rewrite rule for that forwarding class that uses the IEEE 802.1p code point value 011.

Note:

There are no default rewrite rules. You can bind one rewrite rule for DSCP traffic and one rewrite rule for IEEE 802.1p traffic to an interface. A rewrite rule can contain multiple forwarding-class-to-rewrite-value mappings.

  1. To assign a rewrite value to a forwarding class, add the new rewrite value to the same rewrite rule as the other forwarding classes on the port:

    For example, if the other forwarding classes on the port use rewrite values defined in the rewrite rule custom-rw, the forwarding class be2 is being randomly rewritten, and you want to use IEEE 802.1 code point 002 for the be2 forwarding class:

  2. Enable the rewrite rule on an interface if it is not already enabled on the desired interface:

    For example, to enable the rewrite rule custom-rw on interface xe-0/0/24.0:

Related Documentation