Rate and give feedback:  Feedback Received. Thank You!

Rate and give feedback: 

X

This document helped resolve my issue

Yes No

Additional Comments

800 characters remaining

May we contact you if necessary?

Name:  

E-mail: 

Enter a valid Email ID

Need product assistance? Contact Juniper Support

Submit

This site is protected by hCaptcha and its Privacy Policy and Terms of Service apply.

English  

English

Example: Configuring Mesh Groups of IS-IS Interfaces

Understanding IS-IS Mesh Groups

Junos OS supports IS-IS mesh groups as documented in RFC 2973, IS-IS Mesh Groups.

When link-state PDUs are being flooded throughout an area, each router within a mesh group receives only a single copy of a link-state PDU instead of receiving one copy from each neighbor, thus minimizing the overhead associated with the flooding of link-state PDUs.

Mesh groups provide a scaling method for the flooding subsystem. We recommend that you deploy mesh groups when your network design has a dense flooding topology. For example, consider the classical overlay topologies of the 1990s where 200 routers were fully meshed using permanent virtual circuits (PVCs) over an ATM core, because ATM was the only high-speed technology at the time. A PVC is a software-defined logical connection in a network such as a Frame Relay network.

What has changed since the 1990s is that IP and MPLS technology have reduced the ATM layer and removed the need for overlay meshing. The flooding graphs have become sparse in almost all practical deployments. In service provider networks, overlay networks are no longer used.

In enterprise networks, dense flooding graphs that, for example, lease a Layer 2 VPN service (an overlay network) to fully mesh its WAN routers might continue to be a useful architecture. In such cases, mesh groups might be useful.

Example: Configuring Mesh Groups of IS-IS Interfaces

This example shows how to configure mesh groups of IS-IS interfaces.

• Requirements
• Overview
• Configuration
• Verification

Requirements

No special configuration beyond device initialization is required before configuring this example.

Overview

When link-state PDUs are being flooded throughout an area, each router within a mesh group receives only a single copy of a link-state PDU instead of receiving one copy from each neighbor, thus minimizing the overhead associated with the flooding of link-state PDUs.

To create a mesh group and designate that an interface be part of the group, assign a mesh-group number to all the routing device interfaces in the group:

To prevent an interface in the mesh group from flooding link-state PDUs, configure blocking on that interface:

Figure 1 shows the topology used in this example.

Figure 1: IS-IS Mesh Topology

CLI Quick Configuration shows the configuration for all of the devices in Figure 1. The section Step-by-Step Procedure describes the steps on Device R1.

Configuration

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

Step-by-Step Procedure

1. Configure the interfaces.
   [edit interfaces]user@R1# set fe-1/2/0 unit 0 description to-R2user@R1# set fe-1/2/0 unit 0 family inet address 10.0.0.1/30user@R1# set fe-1/2/0 unit 0 family isouser@R1# set fe-1/2/1 unit 0 description to-R4user@R1# set fe-1/2/1 unit 0 family inet address 10.0.0.5/30user@R1# set fe-1/2/1 unit 0 family isouser@R1# set fe-1/2/2 unit 0 description to-R3user@R1# set fe-1/2/2 unit 0 family inet address 10.0.0.9/30user@R1# set fe-1/2/2 unit 0 family isouser@R1# set lo0 unit 0 family inet address 192.168.0.1/32user@R1# set lo0 unit 0 family iso address 49.0002.0192.0168.0001.00
2. Enable IS-IS on the interfaces, and assign a mesh group number.
   [edit protocols isis]user@R1# set interface fe-1/2/0.0 mesh-group 1user@R1# set interface fe-1/2/1.0 mesh-group 1user@R1# set interface fe-1/2/2.0 mesh-group 1user@R1# set interface lo0.0

Results

From configuration mode, confirm your configuration by entering the show interfaces and show protocols commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

If you are done configuring the device, enter commit from configuration mode.

Verification

Confirm that the configuration is working properly.

• Checking the Interface Mesh Group
• Checking the IS-IS Statistics

Checking the Interface Mesh Group

Purpose

Verify that the mesh group is enabled on the IS-IS interfaces.

Action

From operational mode, enter the show isis interface extensive command.

IS-IS interface database:
lo0.0
  Index: 68, State: 0x6, Circuit id: 0x1, Circuit type: 0
  LSP interval: 100 ms, CSNP interval: disabled, Loose Hello padding
  Adjacency advertisement: Advertise
  Level 1
    Adjacencies: 0, Priority: 64, Metric: 0
    Passive
  Level 2
    Adjacencies: 0, Priority: 64, Metric: 0
    Passive
fe-1/2/0.1
  Index: 73, State: 0x206, Circuit id: 0x1, Circuit type: 3
  LSP interval: 100 ms, CSNP interval: 10 s, Loose Hello padding
  Adjacency advertisement: Advertise
   CSNP interval: disabled, Mesh group: 1
  Level 1
    Adjacencies: 1, Priority: 64, Metric: 10
    Hello Interval: 9.000 s, Hold Time: 27 s
    Designated Router: tp5-R2.03 (not us)
  Level 2
    Adjacencies: 1, Priority: 64, Metric: 10
    Hello Interval: 9.000 s, Hold Time: 27 s
    Designated Router: tp5-R2.03 (not us)
fe-1/2/1.0
  Index: 75, State: 0x206, Circuit id: 0x1, Circuit type: 3
  LSP interval: 100 ms, CSNP interval: 10 s, Loose Hello padding
  Adjacency advertisement: Advertise
   CSNP interval: disabled, Mesh group: 1
  Level 1
    Adjacencies: 1, Priority: 64, Metric: 10
    Hello Interval: 9.000 s, Hold Time: 27 s
    Designated Router: tp5-R4.03 (not us)
  Level 2
    Adjacencies: 1, Priority: 64, Metric: 10
    Hello Interval: 9.000 s, Hold Time: 27 s
    Designated Router: tp5-R4.03 (not us)
fe-1/2/2.0
  Index: 76, State: 0x206, Circuit id: 0x1, Circuit type: 3
  LSP interval: 100 ms, CSNP interval: 10 s, Loose Hello padding
  Adjacency advertisement: Advertise
   CSNP interval: disabled, Mesh group: 1
  Level 1
    Adjacencies: 1, Priority: 64, Metric: 10
    Hello Interval: 9.000 s, Hold Time: 27 s
    Designated Router: tp5-R3.02 (not us)
  Level 2
    Adjacencies: 1, Priority: 64, Metric: 10
    Hello Interval: 9.000 s, Hold Time: 27 s
    Designated Router: tp5-R3.02 (not us)

Meaning

Mesh group: 1 in the output shows that the mesh group is enabled as expected.

Checking the IS-IS Statistics

Purpose

Verify that the number of link-state PDUs received and sent is less than what it would be if the mesh group were not enabled.

Action

From operational mode, enter the show isis statistics command.

IS-IS statistics for tp5-R1:
PDU type       Received    Processed        Drops         Sent       Rexmit
LSP                  73           73            0           37            0
IIH                4463           85            0         1525            0
CSNP               1294         1294            0            0            0
PSNP                  0            0            0            2            0
Unknown               0            0            0            0            0
Totals             5830         1452            0         1564            0

Total packets received: 5830 Sent: 1564

SNP queue length: 0 Drops: 0
LSP queue length: 0 Drops: 0
SPF runs: 26
Fragments rebuilt: 15
LSP regenerations: 4
Purges initiated: 0

Meaning

After the adjacencies have been up for about 38 minutes, the output shows that Device R1 has received 73 link-state PDUs and sent 37 link-state PDUs. In the same topology in the same amount of time without the mesh group enabled, Device R1 would have received roughly 156 link-state PDUs and sent roughly 117 link-state PDUs.