Juniper IGP - CONFIGURATION GUIDE V11.1.X, Configuration Manual

Page: 271 / 454

LSDB. OSPF computes routes only to destinations within the area, and does not flood
routes beyond the area boundaries.
Routing Priority
OSPF areas receive routes based on priority. Table 10 on page 247 describes the
routing priority.
Table 10: Routing Priority
Description Type Priority
Intra-area routing. Refers to routing within a single OSPF area. Intra-area 1 (highest)
Interarea routing. Refers to routing between OSPF areas within a
single OSPF routing domain. Interarea 2
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 3
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.
External 4 (lowest)
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.
Virtual Links
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.
Authentication
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.
Features
■ 247
Chapter 5: Configuring OSPF