MPLS LAB1: LDP Adjacency. Part I.

MPLS LAB1: LDP Adjacency. Part I. 

Topics:

• LDP adjacencies and verification
• Hello/Holdtime interval modification.
• LDP autoconfig
• LDP authentication

Gear Specs:

Everything is run over a Dell Latitude with 8GB of Ram, and a Core i7 2640 (2.8ghz).

Platform: 4x Dynamips/GNS3 Emulated Cisco 3745 with 128mb of ram

Topology:

"The serial link will only be used on the second part of the Lab for the IGP-Sync proof of concept."

Initial Configs:

P1:

!

!         

!

interface Loopback0

 ip address 10.1.1.1 255.255.255.255

!

interface FastEthernet0/0

 description Link_to_P2

 ip address 10.0.12.1 255.255.255.248

 ip ospf network point-to-point

 duplex auto

 speed auto

!

interface Serial0/0

 description 2d_link_to_P2

 ip address 10.100.200.1 255.255.255.252

 no fair-queue

 clock rate 2000000

!        

!

!

P2:

!         

!

interface Loopback0

 ip address 10.2.2.2 255.255.255.255

!

interface FastEthernet0/0

 description Link_to_P1

 ip address 10.0.12.2 255.255.255.248

 ip ospf network point-to-point

 duplex auto

 speed auto

!

interface Serial0/0

 description 2d_link_to_P1

 ip address 10.100.200.2 255.255.255.252

 no fair-queue

 clock rate 2000000

!

interface FastEthernet0/1

 description Link_To_P3

 ip address 10.0.23.2 255.255.255.248

 ip ospf network point-to-point

 duplex auto

 speed auto

!

!

P3:

!         

!

interface Loopback0

 ip address 10.3.3.3 255.255.255.255

!

interface FastEthernet0/0

 description Link_to_P4

 ip address 10.0.34.3 255.255.255.248

 ip ospf network point-to-point

 duplex auto

 speed auto

!

!

interface FastEthernet0/1

 description Link_To_P2

 ip address 10.0.23.3 255.255.255.248

 ip ospf network point-to-point

 duplex auto

 speed auto

!

P4:

!

!         

!

interface Loopback0

 ip address 10.4.4.4 255.255.255.255

!

interface FastEthernet0/0

 description Link_To_P3

 ip address 10.0.34.4 255.255.255.248

 ip ospf network point-to-point

 duplex auto

 speed auto

!

!

!

Configuring OSPF:

For all the P routers to know every link address we need to run some Routing protocol above it. In this case we`ll use OSPF.

On all routers

!

router ospf 1

 log-adjacency-changes

 network 0.0.0.0 255.255.255.255 area 0

!

Enabling LDP:

Now we are going to enable LDP , first we`ll test the LDP autoconfig command. Enabling autoconfig should enable ldp on every interface participating in the IGP proccess (OSPF). Autoconfig will be configured on P1 and P2 . P3 and P4 are going to be configured with the interface command mpls ip. This are the main two approaches to configure a LDP adjacency between neighbors.

P1 and P2

!

router ospf 1

 mpls ldp autoconfig area 0

!

!

P3

!

interface FastEthernet0/0

 mpls ip

interface FastEthernet0/1

 mpls ip

!

P4

!

interface FastEthernet0/0

 mpls ip

Verifying on which interfaces is MPLS running:


P1#sh mpls interfaces
Interface              IP            Tunnel   Operational
FastEthernet0/0        Yes (ldp)     No       Yes        
Serial0/0              Yes (ldp)     No       Yes        

P2#sh mpls interfaces 

Interface              IP            Tunnel   Operational

FastEthernet0/0        Yes (ldp)     No       Yes         

FastEthernet0/1        Yes (ldp)     No       Yes         

Serial0/0              Yes (ldp)     No       Yes         

P3#sh mpls interfaces 

Interface              IP            Tunnel   Operational

FastEthernet0/0        Yes (ldp)     No       Yes         

FastEthernet0/1        Yes (ldp)     No       Yes         

P4#sh mpls interfaces 

Interface              IP            Tunnel   Operational

FastEthernet0/0        Yes (ldp)     No       Yes        

After configuring  we should see the following message on each neighbor indicating the establishment of the adjacency 

P1#

*Mar  1 08:43:09.889: %LDP-5-NBRCHG: LDP Neighbor 10.2.2.2:0 (1) is UP

We can verify the neighbors adjacency with the following commands

P1#sh mpls ldp neighbor 

    Peer LDP Ident: 10.2.2.2:0; Local LDP Ident 10.1.1.1:0

TCP connection: 10.2.2.2.32135 - 10.1.1.1.646

State: Oper; Msgs sent/rcvd: 20/20; Downstream

Up time: 00:08:02

LDP discovery sources:

 Serial0/0, Src IP addr: 10.100.200.2

 FastEthernet0/0, Src IP addr: 10.0.12.2

        Addresses bound to peer LDP Ident:

          10.0.12.2       10.100.200.2    10.0.23.2       10.2.2.2        

P3#sh mpls ldp neighbor 

    Peer LDP Ident: 10.2.2.2:0; Local LDP Ident 10.3.3.3:0

TCP connection: 10.2.2.2.646 - 10.3.3.3.23650

State: Oper; Msgs sent/rcvd: 20/20; Downstream

Up time: 00:08:39

LDP discovery sources:

 FastEthernet0/1, Src IP addr: 10.0.23.2

        Addresses bound to peer LDP Ident:

          10.0.12.2       10.100.200.2    10.0.23.2       10.2.2.2        

    Peer LDP Ident: 10.4.4.4:0; Local LDP Ident 10.3.3.3:0

TCP connection: 10.4.4.4.64168 - 10.3.3.3.646

State: Oper; Msgs sent/rcvd: 20/20; Downstream

Up time: 00:08:27

LDP discovery sources:

 FastEthernet0/0, Src IP addr: 10.0.34.4

        Addresses bound to peer LDP Ident:

          10.0.34.4       10.4.4.4        

We can also use the following command show mpls ldp discovery to see which neighbors are being discovered on the enabled interfaces.

P4#sh mpls ldp discovery 

 Local LDP Identifier:

    10.4.4.4:0

    Discovery Sources:

    Interfaces:

FastEthernet0/0 (ldp): xmit/recv

   LDP Id: 10.3.3.3:0

P3#sh mpls ldp discovery 

 Local LDP Identifier:

    10.3.3.3:0

    Discovery Sources:

    Interfaces:

FastEthernet0/0 (ldp): xmit/recv

   LDP Id: 10.4.4.4:0

FastEthernet0/1 (ldp): xmit/recv

   LDP Id: 10.2.2.2:0

Modifying Hello/holtime interval on the LDP adjacency.

First of all we need to verify current values , this is achieved with the following command 

P1#sh mpls ldp parameters 

Protocol version: 1

Downstream label generic region: min label: 16; max label: 100000

Session hold time: 180 sec; keep alive interval: 60 sec

Discovery hello: holdtime: 15 sec; interval: 5 sec

Discovery targeted hello: holdtime: 90 sec; interval: 10 sec

Downstream on Demand max hop count: 255

Downstream on Demand Path Vector Limit: 255

LDP for targeted sessions

LDP initial/maximum backoff: 15/120 sec

LDP loop detection: off

Here we can determine the current values of the hello and holdtime , included the targeted hello and holdtime. currently the values are 15 sec holdtime and hello interval 5 secs. For testing lets modify the current values for the following Hello: 10 and holdtime: 30 on P1 and P2.

P1 and P2:

!

!

mpls ldp discovery hello interval 10

mpls ldp discovery hello holdtime 30

!

!

to verify the changes:

P1#sh mpls ldp parameters 

Protocol version: 1

Downstream label generic region: min label: 16; max label: 100000

Session hold time: 180 sec; keep alive interval: 60 sec

Discovery hello: holdtime: 30 sec; interval: 10 sec

Discovery targeted hello: holdtime: 90 sec; interval: 10 sec

Downstream on Demand max hop count: 255

Downstream on Demand Path Vector Limit: 255

LDP for targeted sessions

LDP initial/maximum backoff: 15/120 sec

LDP loop detection: off

P2#sh mpls ldp parameters 

Protocol version: 1

Downstream label generic region: min label: 16; max label: 100000

Session hold time: 180 sec; keep alive interval: 60 sec

Discovery hello: holdtime: 30 sec; interval: 10 sec

Discovery targeted hello: holdtime: 90 sec; interval: 10 sec

Downstream on Demand max hop count: 255

Downstream on Demand Path Vector Limit: 255

LDP for targeted sessions

LDP initial/maximum backoff: 15/120 sec

LDP loop detection: off

Let us configure LDP authentication Between P3 and P4.

P3: 

!

mpls ldp neighbor 10.4.4.4 password cisco123

!

P4:

!
mpls ldp neighbor 10.3.3.3 password cisco123
!

After configuring the mpls ldp neighbor command we should get the following message.

*Mar  1 09:26:28.665: %LDP-5-NBRCHG: LDP Neighbor 10.4.4.4:0 (2) is DOWN (Session's MD5 password changed)

When the authentication is configured only on one peer we get the following message

 *Mar  1 09:26:34.389: %TCP-6-BADAUTH: No MD5 digest from 10.4.4.4(42183) to 10.3.3.3(646)

After configuring on both ends the LDP adjacency comes back.

P4#

*Mar  1 09:32:21.933: %LDP-5-NBRCHG: LDP Neighbor 10.3.3.3:0 (1) is UP

In the next part we`ll continue with the following topics

• Targeted LDP session.
• Targeted Hello/holdtime interval modification.
• Targeted Sessions with the accept from ACL.
• Advertisement control, outbound, inbound.
• LDP session Protection.