What is the LSA retransmit interval and how to set it


OSPF must send an LSAck packet after receiving a link-state advertisement (LSA). LSAs are retransmitted until they are acknowledged. The link-state retransmit interval defines the time between retransmissions. You can run the ospf timer retransmit interval command to set the retransmit interval. The default interval is 5 seconds.

Other related questions:
What does the OSPF LSA refresh interval mean
When an OSPF link state advertisement (LSA) age reaches the link-state refresh time (1800 seconds), the OSPF updates the LSAs for advertisement.

How long is the LSA refresh interval
Defined in RFC 2328, the 1800-second interval cannot be changed.

What is the purpose of setting the DN bit in an OSPF LSA
If a Provider Edge (PE) device advertises Type-3, 5, and 7 link-state advertisements (LSAs) to Customer Edge (CE) devices through area 0, the optional high-order bit of these LSAs must be set and called the DN bit. If these LSAs are advertised through an area other than area 0, the DN bit can be set or not set. The DN bit is used to prevent routing loops. A PE ignores any LSA whose DN bit is set. This prevents a routing loop caused when a PE learns from the CE the LSA generated by another PE in CE dual-homing scenarios. PE sets the DN-bit of Type 3, 5, and 7 LSAs and checks the DN-bit of Type 3, 5, and 7 LSAs.

OSPF LSA update interval
On S series switches supporting OSPF, OSPF updates and advertises a generated LSA every 1800 seconds (LSA link status update interval). The interval 1800s is defined by RFC 2328 and cannot be modified.

Set the interval at which OSPF LSAs are retransmitted on S series switches
An OSPF-enabled S series switch sends an acknowledgement packet after receiving an LSA packet. If a device does not receive any acknowledgement packet, it retransmits the LSA to its peer device. The link-state retransmit interval parameter specifies the interval at which the LSA is retransmitted. The default value is 5, in seconds. You can run the ospf timer retransmit interval command in the interface view to reset a value.

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