Alcatel Lucent Service Router as an Access Domain Gateway

For many, the first acquaintance with the Alcatel Lucent service routers (now Nokia) is not very pleasant due to the particular vendor look at the service delivery model. Unlike Cisco equipment, it is not always obvious how to make such a device work in a simple scenario: a router for several access switches (usually such switches are connected in a ring). Those who are disappointed, not finding the command spanning-tree in configuration mode, is dedicated.

Imagine a simple topology:


Two access switches connected in a ring with a router, a device with TimOS on board (in this case the SR7750 emulator) and an external DHCP server serving several IP networks. In this situation, the 7750 has several alter egos:

1) Default gateway. PC1 and PC2 quite naturally want to communicate with external networks, so you need to provide them with an IP address where you can send all unwanted packets.
')
2) DHCP realy. As a message, discover is sent by Broadcast; it must be sent to the external server by a unicast message.

3) RSTP root bridge. It is hardly rational to allow the access switch to become root.

Immediately make a reservation that the SR7750 is a router. It is not intended for switching traffic between two interfaces; it does not support SVI in the classical form with all that it implies. To use the device in such a topology, it is necessary to create an improvised and very simple VPLS (although, of course, in the case of two interfaces, a pseudowire would also be suitable). In order to configure VPLS in our case, it is not necessary to understand the principles of MPLS operation.

So let's get started.


0. Our preliminary step will be user configuration. VPLS from the point of view of SR is a service, and any service must belong to the user.

  customer 5 create description "Access ring 1" exit 

1. Configure interfaces 1/1/1 and 1/1/2.

  port 1/1/1 ethernet mode access encap-type dot1q exit no shutdown exit port 1/1/2 ethernet mode access encap-type dot1q exit no shutdown exit 

After that, using the show port command you can verify that the settings are correct. Note that the MTU has become 1518 = 1500 for IP + 14 Ethernet + 4 dot1q vlan. It is quite natural that in the QinQ configuration, the device itself will determine the frame size in 1522.


2. Configure the VPLS service.

 service vpls 5 customer 5 create allow-ip-int-binding stp priority 4096 no shutdown exit service-name "Access-ring-1" sap 1/1/1:5 create exit sap 1/1/2:5 create exit no shutdown exit exit 

SAP (Service access point) is an attachment circuit in slightly better known terminology. The point to which the subscriber device is connected. In our case, the access switch. The number after the colon is the vlan number.

This is where we enable STP. The default mode is RSTP, and our SAP will be point-to-point interfaces from an STP perspective. Priority 4096 set with the intent to turn our pseudo-switch into a root bridge.

allow-ip-int-binding required in order to allow IP interface binding (read SVI) to our VPLS. This interface will be bound using our service name.

Basic verification can be done using show service id 5 base

3. So, the interface.

 service ies 15 customer 5 create interface "DGW-1" create address 10.0.0.6/29 dhcp server 10.10.10.10 relay-unicast-msg no shutdown exit vpls "Access-ring-1" exit exit no shutdown exit 

As you can see, here we killed two birds with one stone: the default gateway was configured, and DHCP clients were provided with DHCP Relay. Note that IES and VPLS are different services, with different id.

Verify that the UP interface is available using show service id 15 interface


4. Configure the interface in the direction of the kernel where the DHCP server is located. For simplicity, we will achieve connectivity with the server by a static route. Do not forget about the value of MTU from the core.

Enable the interface:

  port 1/1/3 ethernet exit no shutdown exit 

Configuring the IP part:

 router interface "To-CORE" address 172.16.0.0/31 port 1/1/3 no shutdown exit interface "system" no shutdown exit static-route 10.10.10.10/32 next-hop 172.16.0.1 

The routing table can be viewed using show router route-table


This is a simple, but slightly unusual setting Alcatel completed. At first glance, VRRP is not enough here, but in an amicable way, to enable VRRP, you need to add an MPLS interface between two routers. In addition to SAP, SDP will be added to our VPLS. But that's another story.

Software Version: TiMOS-B-12.0.R6.
Picture and console: UNL

Thanks for attention.