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.

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.

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.

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.

Common LSA types defined by OSPF of S series switches
Question: What are the common LSAs used in OSPF of S series switches? Why Type 6 LSAs do not exist? Answer: On S series switches supporting OSPF, OSPF uses the following types of LSAs: Type 1 LSA: router LSA Type 2 LSA: network LSA Type 3 LSA: summary LSA Type 4 LSA: ASBR-summary LSA Type 5 LSA: AS-external-LSA Type 7 LSA: NSSA AS-external-LSA OSPF packets were encoded based on Type-Length-Value (TLV). To enable other OSPF functions, you need to use LSAs of other types. Type 6 LSAs, indicating group-membership-LSAs, are used to identify multicast group members in Multicast Open Shortest Path First (MOSPF). Switches do not support Type 6 LSAs. Type 8 LSAs, indicating external-attributes-LSAs, are used to import BGP routes into OSPF processes for inter-operations and reserve information about BGP routes such as AS-Path. Switches do not support Type 8 LSAs. The Opaque LSA type is defined by RFC 2370 and can use the TLV structure. Applications such as OSPF Traffic Engineering (TE) are implemented by the Opaque LSA. The Type 9 LSA is the Opaque LSA flooding on a link. The Type 10 LSA is the Opaque LSA flooding within an area. The Type 11 LSA is the Opaque LSA flooding within an AS.

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.

If you have more questions, you can seek help from following ways:
To iKnow To Live Chat
Scroll to top