Chapter 19
| Unicast Routing
Configuring the Open Shortest Path First Protocol (Version 2)
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problem, you can use the transmit delay to force the router to wait a specified
interval between transmissions.
◆ Retransmit Interval – Sets the time between re-sending link-state
advertisements. (Range: 1-65535 seconds; Default: 5 seconds)
A router will resend an LSA to a neighbor if it receives no acknowledgment after
the specified retransmit interval. The retransmit interval should be set to a
conservative value that provides an adequate flow of routing information, but
does not produce unnecessary protocol traffic. Note that this value should be
larger for virtual links.
Set this interval to a value that is greater than the round-trip delay between any
two routers on the attached network to avoid unnecessary retransmissions.
◆ Authentication Type – Specifies the authentication type used for an interface.
(Options: None, Simple, MD5; Default: None)
Use authentication to prevent routers from inadvertently joining an
unauthorized area. Configure routers in the same area with the same password
(or key). All neighboring routers on the same network with the same password
will exchange routing data.
When using simple password authentication, a password is included in the
packet. If it does not match the password configured on the receiving router,
the packet is discarded. This method provides very little security as it is possible
to learn the authentication key by snooping on routing protocol packets.
When using Message-Digest 5 (MD5) authentication, the router uses the MD5
algorithm to verify data integrity by creating a 128-bit message digest from the
authentication key. Without the proper key and key-id, it is nearly impossible to
produce any message that matches the prespecified target message digest.
The Message Digest Key ID and Authentication Key and must be used
consistently throughout the autonomous system.
◆ Authentication Key – Assign a plain-text password used by neighboring
routers to verify the authenticity of routing protocol messages. (Range: 1-8
characters for simple password or 1-16 characters for MD5 authentication;
Default: no key)
When plain-text or Message-Digest 5 (MD5) authentication is enabled as
described in the preceding item, this password (key) is inserted into the OSPF
header when routing protocol packets are originated by this device.
A different password can be assigned to each network interface, but the
password must be used consistently on all neighboring routers throughout a
network (that is, autonomous system). All neighboring routers in the same
network with the same password will exchange routing data.
◆ Message Digest Key ID – Assigns a key identifier used in conjunction with the
authentication key to verify the authenticity of routing protocol messages sent
to neighboring routers. (Range: 1-255; Default: none)
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