Figure 139: Ospf Areas - Alcatel-Lucent 7750 SR Manual

VPRN Service Configuration Commands
compatible-rfc1583
Syntax [no] compatible-rfc1583
Context config>service>vprn>ospf
Description
This command enables OSPF summary and external route calculations in compliance with RFC1583
and earlier RFCs.
RFC1583 and earlier RFCs use a different method to calculate summary and external route costs. To
avoid routing loops, all routers in an OSPF domain should perform the same calculation method.
Although it would be favorable to require all routers to run a more current compliancy level, this
command allows the router to use obsolete methods of calculation.
The no form of the command enables the post-RFC1583 method of summary and external route
calculation.
Default
compatible-rfc1583 — RFC1583 compliance is enabled.
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The OSPF backbone area, area 0.0.0.0, must be contiguous and all other areas must be connected
to the backbone area. The backbone distributes routing information between areas. If it is not
practical to connect an area to the backbone (see Area 0.0.0.5 in
routers (such as routers Y and Z) must be connected via a virtual link. The two area border
routers form a point-to-point-like adjacency across the transit area (see Area 0.0.0.4).
Area 0.0.0.1
Area 0.0.0.3
RIP Domain

Figure 139: OSPF Areas

Area 0.0.0.0
Y
OSPF Domain
Area 0.0.0.5
7750 SR OS Services Guide
Figure 139) then the area border
Area 0.0.0.2
Area 0.0.0.4
Z