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4321 interface configuration, Metro Ethernet, Point to Multipoint

I changing from managed (AT&T) MPLS to MetroE (self managed).


I have topology like this:

Main Office on MetroE (100Mb) on 3560    192.168.100.x

Branch 1 on MetroE (10Mb) to CE500:       192.168.100.x              (used to be 192.168.120.x while on AT&T MPLS)


Branch 2 MPLS managed AT&T router at both ends    192.168.130.x

Branch 2 End has CE500 connected to AT&T router, Main Office has 3560 connected to the AT&T router.  (same 3560 as MetroE)


I have two vlans at Main Office and Branch 1:

Data: 1

Voice: 2


Everything is working now phones, computers, everything at Main Office and Branch 1.  I haven't converted Branch 2 yet, because I don't know how to setup the interface for multipoint MetroE.

I'm also thinking I want to segment the network with a router for DHCP, Broadcasts, DC, Auth, etc.

If I put 4321's at both ends of MetroE, how do I configure the interfaces on the 4321's.  Point (branches) to Multipoint (Main Office).

Giuseppe Larosa
Hall of Fame Master

Hello EBlodgett,

the metro ethernet service provides you with a virtual single broadcast domain.

No special configuration is needed on the L2 CE nodes that can talk directly between each others.

How the service provider builds the service is transparent to you.

The only point of attention is the following:

the service can be provided at port level or for a single specific vlan-id in 802.1Q tag.

In the first case you are free to use untagged frames or tagged frames and it can support multiple Vlans.

So you could "divide" your flat topology by using Vlan based subinterfaces on the Head office devices.

If the service is vlan based you need to use the specified vlan-id in order to have your frames carried over the metro ethernet service.

Multiple broadcast domains could be built by using 802.1Q tunneling and double Vlan tags but this requires configuration on your switches.


With new service you are not going to peer with the SP for routing purposes (like it happens in MPLS L3 VPN) and you can use the routing protocol that you want your neighbors will be your own devices and not the ISP PE node.

If the number of remote sites is high a flat topology can be a problem.

If you only have two remote offices you can use the flat topology with no problems.


Hope to help




We have 10 remote LANs so I was wanting to put a router for braodcasts plus I'm already setup for different IP's at the remote sites.

I thought about VLAN but I think I'm best served with routers.  I'm just not sure how to setup the interfaces to do that.  At the remote sites, it's a single interface no problem.  I just need help with the configuration of the Main Site router.


Hello Eblodgett,

if you have 10 remote sites there is not a strict need for partitioning.

However, if the provided service is port based all you need to do on HQ routers  is to create subinterfaces one for each remote site using a different Vlan -id.

Please note that the remote site must use a subinterface with the same Vlan-id to build a working configuration.

(again for port based service)


Hope to help





I have a test network setup.


After reading and thinking of the answers here, I decided to try having one 4321 at the HQ and have the remote 2960 MetroE come into sub interfaces on the router.  I created vlans on the remote 2960 and matching sub interfaces on the 4321.


On the 4321, I can ping a pc on the remote 2960 network. On a pc on the 4321 local network, I can only ping the local ip and the local subinterface ip, but not across to remote 2960 interface.


On the remote 2960, I can only ping the 4321's two interfaces, the directly connected subinterface and the interface of the 4321's local network.  A PC on remote 2960 pings across to both ip's on the 4321 subint and 4321 local network.  Both the remote 2960 and the pc connected to the remote 2960 can not ping pass the router to the HQ network.


Am I missing a VLAN setting on the router?