Thank you for asking this question in the support community. There are several ways this design can be implemented, but in large part it depends on the ISP's requirements.
One common configuration is to simply have a WAN IP address and subnet configured on the Ethernet port connected to the ISP's network. This configuration does not need VLANs or trunking configured; only an IP address, subnet mask, and default-route are required for this network design.
Typically, for metro-Ethernet connections such as the one you described, the ISP will instruct you how each WAN facing Ethernet interface should be configured, and what VLANs need to be tagged or untagged. You may only need to configure a trunk port to the ISP, and then have a default-route pointing to them, and they will route all the site-to-site traffic for you.
The Configuring InterVLAN Routing in AOS document explains how to setup a routed Ethernet interface for trunking. Here is an excerpt from that document:
Configuring 802.1q Trunking in the CLI
1. First, access the interface that will be serving as the 802.1q trunk. Then, enable 802.1q mode on the interface. Enable the interface by issuing “no shutdown”.
Syntax: encapsulation 802.1q
Syntax: no shutdown
2. Once 802.1q mode has been enabled on an Ethernet interface, you will be allowed to create multiple subinterfaces. Each subinterface will be the default gateway for devices within that VLAN.
Syntax: interface <interface> 0/1.1
3. Each subinterface must be assigned a VLAN ID. This ID represents the VLAN number that the subinterface is responsible for. Valid IDs fall in the range of 1 to 4094. At least one subinterface must be specified as the “native” VLAN. This VLAN is where all untagged traffic will be tagged to.
Syntax: vlan-id <vlan number>
Syntax: vlan-id <vlan number> native
4. Finally, each subinterface must be assigned an IP address. This IP must reside in the desired subnet for the VLAN that has been assigned to it. After the assignment, the interface can be activated by issuing “no shutdown”.
(config-eth 0/1.1)# ip address <A.B.C.D> <subnet mask>
(config-eth 0/1.1)# no shutdown
Please, do not hesitate to reply with any additional questions, I will be happy to help in any way I can.
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