Advanced Juniper Networks Routing
Release 5.1, Revision 0
Module 5: IS-IS Multi-Area Networks
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
Copyright © 2001, Juniper Networks, Inc.
IS-IS Level 2 Network
L2
L2
L2
L2
L2
L2
L2
L2
L2
L2
Area 49.1111
L2
L2
Area 49.2222
Copyright © 2001, Juniper Networks, Inc.
Area 49.3333
IS-IS Level 1 Network
L1
L1
L1
L1
L1
L1
L1
L1
L1
L1
L1
Area 49.4444
Copyright © 2001, Juniper Networks, Inc.
L1
IS-IS Level 1 & Level 2 Network
L1
L1
L2
L2
L2
L2
L1
L1
L1
L1
L2
L1
L1
L2 L1
L2
Area 49.5555
L1 L2
Area 49.6666
Copyright © 2001, Juniper Networks, Inc.
L1
L1
Area 49.7777
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
level
}
interface
level
}
interface
}
}
so-0/0/0.0 {
1 disable;
ge-0/1/0.0 {
2 disable;
lo0.0;
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
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;
}
}
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;
}
}
Copyright © 2001, Juniper Networks, Inc.
Review Questions
Copyright © 2001, Juniper Networks, Inc.