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Virtual Links
Authentication
Copyright © 2010, Juniper Networks, Inc.
Routing Priority
OSPF areas receive routes based on priority. Table 10 on page 241 describes the routing
priority.
Table 10: Routing Priority
Priority
Type
1 (highest)
Intra-area
2
Interarea
3
External
4 (lowest)
External
If you use the redistribute command to import routes from other protocols or sources,
the routes default to external type 2. You can specify a route map with the redistribute
command to modify the type. Alternatively, you can use the metric-type keyword with
the redistribute command to specify the type.
Each OSPF area must be directly connected to the backbone area. The backbone is
responsible for distributing routing information between nonbackbone areas. All routers
in the backbone must be contiguous, but they need not be physically adjacent. You can
configure backbone routers to be logically adjacent by creating OSPF virtual links.
OSPF supports three modes of authentication:
Null authentication—Implies that no authentication is in use.
Simple password authentication—Requires a 64-bit unencrypted password in each
OSPF packet.
Cryptographic authentication—Uses a shared secret key that is configured on each
router on a network. RFC 2328 defines the use of OSPF cryptographic authentication
with the MD5 algorithm.
Description
Intra-area routing. Refers to routing within a single OSPF area.
Interarea routing. Refers to routing between OSPF areas within a
single OSPF routing domain.
External type 1. Refers to routing from other protocols that can be
imported into the OSPF domain and readvertised by OSPF as type
1 external.
Type 1 metric is comparable to the link-state metric; the cost is equal
to the sum of the internal costs plus the external cost.
External type 2. Refers to routing from other protocols that can be
imported into the OSPF domain and readvertised by OSPF as type
2 external.
Type 2 metric is much larger than the cost of any intra-AS path; the
cost is equal to the external cost. This is the OSPF default.
Chapter 5: Configuring OSPF
241
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