QinQ with Cisco Catalyst switches

Below a simple topology using QinQ tagging (officially known as IEEE 802.1ad or unofficially IEEE 802.1 QinQ ) on Cisco Catalyst C3550 switches.

C-VLANS 10 and 20 come from customer side and are encapsulated in the S-VLAN 1800.

This feature is also called VLAN double tagging or Vlan stacking, or Nested VLANs (Allied Telesis) or vMAN technology ( Extreme Networks).

Rate Limit on Cisco 3550

I have a Cisco 3550 and  want to apply rate limit on the interfaces for both ingress and egress. 
As per Cisco documentation in
Understanding QoS Policing and Marking on the Catalyst 3550
"Policing is not to be confused with traffic shaping, although both make sure the traffic stays within the profile or contract.
Policing does not buffer the traffic, so policing does not affect the transmission delay. Instead of buffering out-of-profile packets, policing drops them or marks them with different QoS levels (DSCP markdown).

Traffic shaping buffers out-of-profile traffic and smoothes the traffic bursts, but affects the delay and delay variation. Shaping can only be applied on the outgoing interface, while policing can be applied on both the incoming and outgoing interface.

The Catalyst 3550 supports policing for both incoming and outgoing directions. Traffic shaping is not supported."

Basic DHCP on Cisco Router

Configuring DHCP IOS DHCP server

Sequence of DHCP messages :

1. Client sends a broadcast DHCPDISCOVER message to the server
2. The DHCP server replies with a DHCPOFFER message containing the IP address, subnet mask , gateway and other parameters.
3. The client sends a broadcast DHCPREQUEST message to the server, requesting the offered address.
4. The DHCP server replies with a broadcast DHCPACK packet to the client.

DHCP server was designed to work within the same broadcast domain as the clients.
If DHCP server is behind another router , that router must become a DHCP Relay Agent. The DHCP relay will intercept the broadcast DHCP messages from the client and will forward them to the server as unicast messages. See at the end of this post a setup based on this scenario.

My network setup in GNS3 shown below 

Cisco Routers/Switches - Command alias

You can create command alias on Cisco routers/swithces by using the command alias in the global configuration mode

See the origal documentation by Cisco Systems :
Using Aliases for CLI Commands

Cisco IOS Configuration Fundamentals Command Reference - alias

Syntax :
alias mode command-alias original-command
no alias mode [command-alias]