Specifications

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Cisco Nexus 3000 Series NX-OS Unicast Routing Configuration Guide, Release 5.0(3)U2(2)
OL-25782-02
Chapter 3 Configuring OSPFv2
Information About OSPFv2
Simple Password Authentication
Simple password authentication uses a simple clear-text password that is sent as part of the OSPFv2
message. The receiving OSPFv2 router must be configured with the same clear-text password to accept
the OSPFv2 message as a valid route update. Because the password is in clear text, anyone who can
watch traffic on the network can learn the password.
MD5 Authentication
You should use MD5 authentication to authenticate OSPFv2 messages. You configure a password that is
shared at the local router and all remote OSPFv2 neighbors. For each OSPFv2 message, Cisco NX-OS
creates an MD5 one-way message digest based on the message itself and the encrypted password. The
interface sends this digest with the OSPFv2 message. The receiving OSPFv2 neighbor validates the
digest using the same encrypted password. If the message has not changed, the digest calculation is
identical and the OSPFv2 message is considered valid.
MD5 authentication includes a sequence number with each OSPFv2 message to ensure that no message
is replayed in the network.
Advanced Features
Cisco NX-OS supports a number of advanced OSPFv2 features that enhance the usability and scalability
of OSPFv2 in the network. This section includes the following topics:
• Stub Area, page 3-8
• Not-So-Stubby Area, page 3-9
• Virtual Links, page 3-9
• Route Redistribution, page 3-10
• Route Summarization, page 3-10
• OSPFv2 Stub Router Advertisements, page 3-11
• Multiple OSPFv2 Instances, page 3-11
• SPF Optimization, page 3-11
• Virtualization Support, page 3-11
Stub Area
You can limit the amount of external routing information that floods an area by making it a stub area.
A stub area is an area that does not allow AS External (type 5) LSAs (see the “Link-State
Advertisements” section on page 3-5). These LSAs are usually flooded throughout the local autonomous
system to propagate external route information. Stub areas have the following requirements:
• All routers in the stub area are stub routers. See the “Stub Routing” section on page 1-7.
• No ASBR routers exist in the stub area.
• You cannot configure virtual links in the stub area.
Figure 3-3 shows an example of an OSPFv2 autonomous system where all routers in area 0.0.0.10 have
to go through the ABR to reach external autonomous systems. area 0.0.0.10 can be configured as a stub
area.