Learn the correct configuration for IEEE 802.1ad on a Cisco router access port handling multiple customer VLANs without dropping traffic. Discover the key differences between s-port, c-port, and nni options.
Table of Contents
Question
An engineer is configuring IEEE 802. 1ad on the access port on a new Cisco router. The access port handles traffic from multiple customer VLANs, and it is expected to mark allcustomer traffic to the same VLAN without dropping any traffic. Which configuration must the engineer apply?
A. interface gigabitethernet0/0/1 ethernet dot1ad uni s-port
B. interface gigabitethernet0/0/1 ethernet dot1ad uni c-port
C. interface gigabitethernet0/0/1 ethernet dot1ad uni nni
D. interface gigabitethernet0/0/1 encapsulation dot1q 10
Answer
B. interface gigabitethernet0/0/1 ethernet dot1ad uni c-port
Explanation
When configuring IEEE 802.1ad on a Cisco router access port that handles traffic from multiple customer VLANs, the correct configuration is to use the “ethernet dot1ad uni c-port” command on the interface.
The “c-port” (customer port) option allows the access port to receive untagged or tagged frames from multiple customer VLANs and add an IEEE 802.1ad service tag (S-tag) to each frame before forwarding them. This ensures that all customer traffic is marked with the same S-tag VLAN ID without dropping any frames.
The other options are incorrect for the given scenario:
- Option A: “s-port” (service port) is used on the network-facing side of the service provider bridge, not on the access port facing the customer.
- Option C: “nni” (network-to-network interface) is used for connecting service provider bridges, not for the access port configuration.
- Option D: “encapsulation dot1q” is used for IEEE 802.1Q tunneling (QinQ) and does not apply to IEEE 802.1ad (QinQ-in-Q) configuration.
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