In what case does an OSPF LSDB have a large number of LSAs that cannot be aged

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When the available memory of a switch is low, the SOCK first send packets in high-priority queues to the CPU. When the available memory is very low, the SOCK sends only Hello packets to the CPU. As a result, LSAs in the OSPF LSDB cannot be updated. When the age of LSAs reaches 3600s, OSPF cannot calculate routes. Because ACK packets are not sent to the CPU, LSAs in the LSDB cannot be aged.

To address this problem, you can adjust the memory usage threshold, delete unwanted sub-interfaces, and expand memory capacity.

Other related questions:
Why cannot an OSPF route contained in the LSDB/LSA be queried in the routing table on an S series switch
Question: Why cannot an OSPF route contained in the LSDB/LSA be queried in the routing table? Answer: Perform the following operations on the S series switch to solve the problem. Check whether the IP address is valid. Check whether the forwarding address is known and reachable. Check whether the route aggregation or route import is correct. Check whether a different mask or IP address is used in P2P connection. Check whether the advertise route list is configured. Check whether the connection with the backbone area is proper. Check whether OSPF is enabled on the secondary IP address instead of the primary IP address.

What does the TOS field in an OSPF LSA indicate
The TOS field in an OSPF LSA was designed for QoS routing. Packets with different TOS values are transmitted on links with different cost values, enabling TOS-based routing. That is, IP packets with the same destination but different TOS values are forwarded on differentiated routes. This application, however, is canceled in RFC 2328. The OSPF devices support only TOS value 0. That is, the route is based only on destination IP address.

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.

Why cannot an OSPF route that exists in the LSDB be found in the routing table
Perform the following steps to solve this problem: Check whether the IP address is valid. Check whether the forwarding address is known and reachable. Check whether the routes are summarized or redistributed correctly. Check whether different masks or IP addresses are used in the Peer-to-peer (P2P) connection. Check whether route lists are advertised. Check whether the backbone area is disconnected. Check whether OSPF is enabled on the secondary address but not on the primary address. Parent topic: IP Routing

Common LSA types of OSPF
Common LSA types of OSPF are as follows: Type 1 LSA: router LSA. Generated by each router, describes the router's link status and cost, and advertised within the area to which it belongs. Type 2 LSA: network LSA. Describes the link status of all routers on the local network segment. Network-LSAs are generated by a designated router (DR) and advertised within the area to which the DR belongs. Type 3 LSA: summary LSA. Generated by ABR, describes all routes in the area, and advertised to other relevant areas. Type 4 LSA: ASBR-summary LSA. An ASBR-summary-LSA describes routes to the ASBR in an area. The routes are advertised to all areas except the area to which the ASBR belongs. Type 5 LSA: AS-external-LSA. Describes AS external routes, which are advertised to all areas except stub areas and NSSAs. AS-external-LSAs are generated by an ASBR. Type 7 LSA: NSSA AS-external-LSA. Describes AS external routes. NSSA-LSAs are generated by an ASBR and advertised only within NSSAs. The original OSPF packet coding is not Type Length Value (TLV)-based. For the extension of OSPF functions, only the LSA types of OSPF can be extended. Type 6 LSAs are Group-Membership-LSAs used to identify multicast group membership in the Multicast Open Shortest Path First (MOSPF) protocol. Type 6 LSAs are not supported on the firewall. Type 8 LSAs are External-Attributes-LSAs used to redistribute Border Gateway Protocol (BGP) routes into OSPF and reserve the BGP autonomous system (AS) path information. Type 8 LSAs are not supported on the firewall. RFC 2370 defines an important LSA type, namely, Opaque LSA, which allows for TLV-like structures. OSPF applications, such as OSPF traffic engineering, are based on the Opaque LSA extension abilities: Type 9 LSAs are Opaque LSAs that are advertised within the local link only; Type 10 LSAs are Opaque LSAs that are advertised within the local area only; Type 11 LSAs, similar to Type 5 LSAs, are Opaque LSAs that are advertised within the local AS.

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