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By Tatiane Figueiredo - Training Instructor

As you have accompanied on our blog, traffic engineering applied to MPLS networks has the purpose of optimizing current resources on your network, solving some limitations present in traditional routing or even in topologies where MPLS is used only in the protocol LDP - Label Distribution Protocol.

These limitations are attached to the protocol building itself, thinking about routing, there is the use of few paths, since the protocol metric will use the best or the minor cost to the destination, and can leave idle links. Already the MPLS infrastructure built only with LDP, which is a specific protocol and responsible for the distribution of Labels defined by the IETF in RFCs 3036 and 3037, is characteristic to use the best path defined in the layer protocol 3, consequently, also not exploring the entire Potential of available links.

 

 

In this scenario, there is no way to accommodate all the load of the desired traffic, thus causing congestion, which directly impacts on the quality of the client offered.

In articles, MPLS: Traffic engineering with RSVP-TE and 5 reasons to use MPLS on your provider, you can check more benefits and characteristics of the use of these features. In this text, we would like to dedicate a space to talk about the creation of MPLS-tunnels based on the explicit-path criteria.

The idea of ​​traffic engineering in MPLS networks is to seek the most efficient use of resources present in the provider's infrastructure, such as equipment already installed, reducing the idleness of own or contracted links and the best balancing of traffic load between the various interfaces / transceivers speeds.

The tunnel is unidirectional, similar to the behavior of LSP - Label Switch Path. Only the device called Head End receives the configuration of the explicit path of the tunnel TE facilitating the administration of VPNs and all referral is based on labels.

And for the MPLS-MPLS operates correctly, it is necessary that the IGP - Interior Gateway Protocol is able to send the link state to the other devices present in the area where you were enabled. The RFC 3630 specifies the addition of extensions to the OSPF protocol for operation and RFC 2370 defines the improvements of the OSPF protocol to support a new class of link status, the LSA - Link-State advertisements called opaque. For the MPLS-you are used in specific LSA TYPE 10 opaque, which covers your performance to an OSPF area.

The explicit-path, as the name itself indicates is the definition of paths explicitly from the head end to the tail end and consists of two types of routes:

 

1. Strict Route:

It consists of the orderly declaration of all the way to be traveled, jumping-by-jump. The tunnel will obey faithful and strictly to the path determined in the configuration and not indicated by routing.

There may be no undeclared jumps on the path between the Head End and the Tail End, all informed IP addresses should be directly connected.

 

2. Loose Route:

It is not necessary to determine all jumps between Head End and Tail End, but rather, intermediate IP addresses such as mandatory and strategic points for the formation of the LSP, thus allowing freedom to form the path between the two of us dynamically, according to the best route established by the routing protocol.

Here, the equipment does not need to be connected directly. Choosing the path, will be a combination between the routing table and the informed IP address.

Regardless of the choice by Strict Route or Loose Route, the Labels Request process starts in the Head End and goes on the way to reach the Tail End through RSVP Path messages. On the reverse path, the Tail End sends a RSVP Message to containing the information.

After messaging, an RSVP session or a MPLS tunnel will be established.

 

What settings are involved for using explicit-path in DmOS?

Initially, the VLANs involved in the network infrastructure, with their respective IPS addresses through the L3 interface (Layer 3 / Layer 3) and the creation of a loopback interface.

In all switches, within the OSPF configuration, associate the MPLS option with the loopback interface, in addition to the traditional configuration and good practices involved. This configuration is required for the OSPF to send through the LSA TYPE 10 opaque the link state and the TLVs - TYPE Length values required for the operation of the TE.

In the sequence, associate the L3 interfaces (Layer 3 / Layer 3) to the RSVP MPLS. The information of each link will be disclosed through the OSPF. The RSVP protocol defines the path and signals the tunnel based on OSPF information.

From this time it is possible to set the tunnels, remember that this operation is performed only in the Head End. Only tunnels are supported in the same OSPF area (intra-area).

The priority order of the paths is defined by the associated ID, the smaller, more priority, that is, it will have its execution performed from the smallest to the highest ID.

The equipment with Operating System DmOS allow you to combine loose and strict Hops in the same path. If the characteristic of the Explicit-Path path is not specified, they will be assumed that Hop is Strict. It should be noted that for the loose option it is not necessary to define hop a hop.

Now we need to inform the characteristics of the tunnel interface.

The idea or the possibility of using more than one path-option creates protection for the "main" LSP, allowing in case of traffic transportation in another way.

 

Demonstration time

The topology we use as reference for the settings is observed below.

For the demonstration of all the settings involved, from the creation of VLANs to the Tunnel interface associated with the explicit-path, we will use the equipment flagged by DmOS-1, positioned as the circuit's head end in the DmOS-1 direction DmOS-3.

The interface associated with VLAN of infrastructure may be an individual port or an aggregation of links, as displayed below.

The link-aggregation may be of the static type, as viewed in LAG 2 or the dynamic type with Active / Passive (LACP) protocol in the LAG 1 configuration.

After you create VLAN, you will need to associate it with an IP address through the L3 Interface (Layer 3 / Layer 3) feature. A mask was used / 31 Seen the need for only two IP addresses to form the point-to-point link. The mask / 30 may also be used, according to the address plan of your topology.

Following, create a loopback interface, which will be associated with the OSPF configuration and later than MPLS.

Perform the traditional OSPF routing protocol settings. Note that we introduce the syntax "MPLS-te router-ID loopback-0", which has the function of generating LSA TYPE 10 (area-local "OPAQUE" LSA), which is defined by RFC 2370 and used for MPLS extensions TE TODS that the OSPF can create the traffic engineering database, with links about links.

The MPLS-te requires the LDP settings for the generation of VC labels - Virtual Container that occurs by adding the syntax "L3-

Add the L3 (Layer 3 / Layer 3) interfaces to the RSVP MPLS configuration block, so that MPLS signaling is routed.

Tunnels will be associated with two paths for transporting customer traffic. The main will be in the direction of DmOS-2 equipment, signaled by green color. If a failure occurs, the tunnel will be directed to the secondary, which will pass through the DmOS-4 and DmOS-5 equipment flagged in red color.

For the demonstration, the Strict option is used, where it is necessary to inform the IP address of the L3 interface (layer 3 / layer 3) of the next hop, detailing the IPs all the way to be traveled.

In the configuration below, Path-Option 10 has priority on path-option 20. The direction of the configuration obeys the DmOS-1 >> DmOS-3 stream.

Create the tunnel interface and associate the Explicit-Path.

The priority order of the path use is defined by the number / ID associated with the tunnel path-option. For example, Path-Option 10 has priority over path-option 20 and so on.

And with this, we finish the DmOS-1 equipment settings. Repeat the above operations in the equipment identified as DmOS-3, as the tunnels are unidirectional.

In the equipment flagged by the Names / Hostnames DmOS-2, DmOS-4 and DmOS-5 In addition to the VLAN settings, L3 interface, OSPF with the syntax "MPLS-te Router-ID loopback-0", add within the "MPLS RSVP "The L3 interfaces that will be part, as below.

Next, you can check out the top commands for Troubleshooting.

 

1. Verification of infrastructure label generated by the RSVP protocol

This command allows you to view the actions to be performed for each of the neighbors. Featured, in the last line there is the push action, where customer traffic reaches the equipment without label (in label -) and output, there is insertion of label 72.

Note that the LSP output will occur by the RSVP protocol in the direction of VLAN 2122, which is the main path defined in the Path-Option of the Tunnel interface.

If the drop in a link that prevents the establishment of the path defined as the main path, we will have a second option, located in the configuration as a secondary path. By simulating a link in the link between the DmOS-2 and DmOS-3 equipment (main tunnel path), we will have the convergence being established by the DmOS-1 >> DmOS-5 >> DmOS-4 >> DmOS-3 viewed below and in other checks.

2. Tunnel Interface Status

Here we can check the status of the tunnel interface, including in the direction tail end >> Head End arranged on the second line of the show below.

The last row displays the backup path or secondary path, according to the configuration performed within the Tunnel Interface block.

When there is some failure in Path-Option of the way, the traffic will be directed to the path-option path-option, as observed below.

 

3. Detailing of the Tunnel Interface Status

To check the source and destination of the tunnel, in addition to the chosen attribute and which path is active and forwarding traffic, use the syntax below.

In case of failure of the main path - path_1, we verified below the performance of Path_2, as well as the new jumps / paths assumed.

4. Consultation at LSA 10 opaque

In the show below we observed the result of the OSPF database facing LSS Type 10, which we address, are required for the correct operation of the MPLS-TE.

Through the IP Show OSPF Database Opaque-Area Detail You can check the details of each of the above LSAs.

 

5. Debugging Messages

You can activate debugging messages, known as Debug, for the protocol analysis and very useful in the problem situation.

After activation, a failure occurs in the protocol or some that fall from a link that causes convergence, we will have:

6. Equipment logs

All the amendment occurred in the tunnel interface, as well as in the protocols involved, as RSVP can be consulted in the equipment logs.

With the completion of the configuration and after the analysis of all available scans, associate the desired tunnel interface with your Layer 2 VPN, either VPWs - Virtual Private Wire Service or VPLS - Virtual Private LAN Service. Below, we view an example.

You have given this article, that the use of MPLS allied traffic engineering has a better use of the resources of your network through the analysis and establishment of attributes that facilitate management. For more details regarding DmOS configuration, see our documentation.

The Explicit-Path functionality is available in DmOS from version 7.2. Switches supporting this feature are: DM4360, DM4370, DM4170, DM4380, DM4270 and DM4770.

Remembering that Datacom has a complete structure in your matrix where face-to-face trainings are offered (see availability with the commercial team due to the pandemic scenario) as well as a platform for online training (Datacom EAD). In training you will be able to make configurations of various topologies and application scenarios, besides being able to count on the help of our professionals in a series of good practices that will help a lot in the operation of your network.

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