1. Release 5.1, Revision 0 Copyright © 2001, Juniper Networks, Inc. Advanced Juniper Networks Routing Module 5: IS-IS Multi-Area Networks

2. Copyright © 2001, Juniper Networks, Inc. Module Objectives Review the basic components and functionality of the IS-IS Protocol Take a look at the IS-IS addressing schemes and the different topology levels Discuss neighbor adjacency formations Configure IS-IS on a Juniper Networks router

3. Copyright © 2001, Juniper Networks, Inc. IS-IS Level 2 Network Area 49.1111Area 49.2222Area 49.3333 L2

4. Copyright © 2001, Juniper Networks, Inc. IS-IS Level 1 Network Area 49.4444 L1

5. Copyright © 2001, Juniper Networks, Inc. IS-IS Level 1 & Level 2 Network Area 49.5555Area 49.6666Area 49.7777 L2 L1 L2 L1 L2 L1 L2 L1

6. Copyright © 2001, Juniper Networks, Inc. IS-IS Multi-Level Configuration Each IS-IS interface operates at both Level1 and Level2 by default Disable a specific level to NOT have the interface operate at that level protocols { isis { interface so-0/0/0.0 { level 1 disable; } interface ge-0/1/0.0 { level 2 disable; } interface lo0.0; }

7. Copyright © 2001, Juniper Networks, Inc. Multi-Level Operation A L1L2 IS-IS network operates in a similar fashion to an OSPF NSSA no-summaries network – Local L1 routes are advertised into L2 areas – External routes can be advertised into a L1 area The L1L2 area border is a natural route boundary – L2 routes are not advertised to a L1 area – External L1 routes are not advertised to a L2 area L2 routers that connect to another L2 area set the attached bit in their LSPs L1 routers set a local 0/0 default route to the closest L2 attached router

8. Copyright © 2001, Juniper Networks, Inc. Route Leaking A policy is used to advertise routes across a L1L2 area border Routes advertised from a L2 area into a L1 area have the Up/Down bit set to down – Allows a second L2 router to NOT readvertise the route back into a L2 area – Avoids routing loops [edit policy-options] user@host# show policy-statement route-leak { term L2-to-L1 { from { protocol isis; level 2; route-filter 192.168.16.0/20 orlonger; } to level 1; then accept; }

9. Copyright © 2001, Juniper Networks, Inc. Route Summarization The L1L2 area border is a good place to summarize routing information – Only routes “allowed” by a route leaking policy can be summarized – Default route flooding occurs at the LSP “level” Aggregate routes are created in the local routing table A policy is used to advertise those routes [edit policy-options] user@host# show policy-statement isis-summary { term on-the-l1l2-router { from { protocol aggregate; route-filter 172.16.20.0/22 exact; } then accept; }

10. Copyright © 2001, Juniper Networks, Inc. Review Questions