LevelOne GTL-2691 User Manual

Page 693

HAPTER

| Unicast Routing

Configuring the Open Shortest Path First Protocol (Version 2)

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Transmit Delay – Sets the estimated time to send a link-state update

packet over an interface. (Range: 1-65535 seconds; Default: 1 second)
LSAs have their age incremented by this delay before transmission. You

should consider both the transmission and propagation delays for an

interface when estimating this delay. Set the transmit delay according

to link speed, using larger values for lower-speed links.
If this delay is not added, the time required to transmit an LSA over the

link is not taken into consideration by the routing process. On slow

links, the router may send packets more quickly than devices can

receive them. To avoid this problem, you can use the transmit delay to

force the router to wait a specified interval between transmissions.

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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.

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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 pre-specified target message digest.
The Message Digest Key ID and Authentication Key and must be used

consistently throughout the autonomous system.

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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