ECMP Configuration on Nokia Routers

We have learned what is ECMP (Equal Cost Multi Path) before. Here, we will talk about ECMP Configuration on Nokia Routers. To explain ECMP better, we will use the below MPLS Topology.

As you can see, from Router A to Router B, there are three different ways. Normally, without ECMP, the MPLS traffic from Router A to Router B, go through one of these paths. This path is the “Best Path” that is elected by your Routing Protocol. This path is showed in FIB (Forwarding Information Base). One of these paths is elected and the LDP Tunnelis established only over it. Can you see? How an inefficient use!

In such situations, Equal Cost Multi Path comes to help us. With this ECMP mechanims, we can efficiently use our paths towards to a destination. It allocated the traffic between the available links equally. Here, in our ECMP configuration, MPLS traffic will go through these three paths. With this mechanism.

Before configuring ECMP, let’s check the FIB and LDP Bindings. On FIB, only the Best Path exists.

A:RouterA# show router fib 1

==============================================================
LDP Prefix Bindings
==============================================================
Prefix NextHop Protocol
-----------------------------------------------------------------------------------------------------
10.10.10.10/32 192.168.1.2 OSPF
-----------------------------------------------------------------------------------------------------

LDP Binding of all the peers are given below.

A:RouterA# show router ldp bindings

==============================================================
LDP Prefix Bindings
==============================================================
Prefix Peer IngLbl EgrLbl EgrIntf/ EgrNextHop
-----------------------------------------------------------------------------------------------------
10.10.10.10/32 1.1.1.1 274348N 274351 1/1/1 192.168.1.2
10.10.10.10/32 2.2.2.2 274349U 274352 1/1/2 192.168.2.2
10.10.10.10/32 3.3.3.3 274350U 274353 1/1/3 192.168.3.2
-----------------------------------------------------------------------------------------------------

There is only one Active binding as you can see.

A:RouterA# show router ldp bindings active

==============================================================
LDP Prefix Bindings (Active)
==============================================================
Prefix Op IngLbl EgrLbl EgrIntf/ EgrNextHop
-----------------------------------------------------------------------------------------------------
10.10.10.10/32 Push -- 274351 1/1/1 192.168.1.2
-----------------------------------------------------------------------------------------------------

Now, let’s start our ECMP Configuration on Nokia Service Routers example and see the change after our configuration. Above, we saw the tables without ECMP. After the ECMP configuration, we will see tables affected by ECMP.

We will configure ECMP on the global router level. And we will use ECMP for three routers.

A:RouterA# configure

A:RouterA>config# router ecmp ?
- ecmp
- no ecmp
: [0..16]

A:RouterA>config# router ecmp 3

Here, we said to our router that, “Use three path for ECMP and divide traffic between them equally.” ECMP Equal Multi Path can be used up to 16 routers.

After our ECMP configuration, our FIB (Forwarding Information Base) will include all of these links and LSP Tunnels are established on all these three links as you can see below. The MPLS traffic will go through all these links.

On FIB, all the links can be seen.

A:RouterA# show router fib 1

==============================================================
LDP Prefix Bindings
==============================================================
Prefix NextHop Protocol
-----------------------------------------------------------------------------------------------------
10.10.10.10/32 192.168.1.2 OSPF
10.10.10.10/32 192.168.2.2 OSPF
10.10.10.10/32 192.168.3.2 OSPF
-----------------------------------------------------------------------------------------------------

LDP bindings are still in the table with one difference. Here, the Ingres Label of all these LSPs aresame.

A:RouterA# show router ldp bindings

==============================================================
LDP Prefix Bindings
==============================================================
Prefix Peer IngLbl EgrLbl EgrIntf/ EgrNextHop
-----------------------------------------------------------------------------------------------------
10.10.10.10/32 1.1.1.1 274348N 274351 1/1/1 192.168.1.2
10.10.10.10/32 2.2.2.2 274348N 274352 1/1/2 192.168.2.2
10.10.10.10/32 3.3.3.3 274348N 274353 1/1/3 192.168.3.2
-----------------------------------------------------------------------------------------------------

And the most important part. You can see the active LDP bindings below. All the links are active as you can see.

A:RouterA# show router ldp bindings active

==============================================================
LDP Prefix Bindings (Active)
==============================================================
Prefix Op IngLbl EgrLbl EgrIntf/ EgrNextHop
-----------------------------------------------------------------------------------------------------
10.10.10.10/32 Push -- 274351 1/1/1 192.168.1.2
10.10.10.10/32 Push -- 274352 1/1/2 192.168.2.2
10.10.10.10/32 Push -- 274353 1/1/3 192.168.3.2
-----------------------------------------------------------------------------------------------------

You Can Test Yourself With Nokia NRS I Quizes and Nokia NRS II Quizes.