Information Technology Reference
In-Depth Information
9.
IS-IS = Intermediate System-to-Intermediate System
10.
LSP = Link State Protocol
ISO CLNS: Host Cannot Access Hosts in Same Area
Symptom:
Hosts cannot access other hosts in the same area. The hosts might be on the same network
or they might be in a different network in the same area.
Table 12-4 outlines the problems that might cause this symptom and describes solutions to those
problems.
Table12-4 ISO CLNS: Host Cannot Access Hosts in Same Area
Possible Problem
Solution
Area address is
configured
incorrectly on the
host
Check all Level 1 routing tables and link-state databases.
1.
Verify that the hosts are in the same area.
2.
Check that the NSAP address is entered correctly on the
hosts.
3.
Different area
addresses are
merged into a
single area, but
the router is
configured
incorrectly
1.
Use the
show running-config
privileged exec command to
see router configurations. Check whether multiple area
addresses are configured.
2.
If multiple network addresses are configured, verify that the
router is configured to support a multihomed area
(a single area that has more than one area address; see
Figure 12-3).
3.
To communicate, routers must establish a Level 1 adjacency.
Therefore, area addresses in a multihomed area must overlap
across routers.
For example, in the multihomed area shown in Figure 12-3, to
configure Area 1 and Area 2 as a multihomed area, both
Router A and Router B must be configured to be in both areas.
IS-IS routing supports the assignment of multiple area addresses
on the same router. This concept is referred to as
multihoming
.
Multihoming provides a mechanism for smoothly migrating
network addresses, as follows:
Splitting up an area—Nodes within a given area can
accumulate until they are difficult to manage, cause
excessive traffic, or threaten to exceed the usable address
space for an area. Multiple area addresses can be assigned so
that you can smoothly partition a network into separate areas
without disrupting service.
•
Merging areas—Use transitional area addresses to merge as
many as three separate areas that have a common area
address into a single area.
•
continues
