Setting a static RID helps reduces LSAs when RID change

[hfakoor222]

Reading ENARSI exam book and it mentions for OSPF

Setting a static RID helps with troubleshooting and reduces LSAs when an RID changes in
an OSPF environment.

I don't understand the logic of LSA reduction, by making it static. The RID doesn't change until the process is restarted, so how does setting a static RID reduce the LSA's, if the RID is being changed in either case?

Any insight appreciated,

Thanks

[David Ruess]

One scenario that comes to mind is graceful restart. OSPF neighbors will keep the LSAs of the neighbor going through a graceful restart and when it comes back up it doesn't have top flood (except any new information) out to its peers. However, if the OSPF RID has changed this would require a re-flood of all LSAs saturating the network while OSPF converged.

Keep in mind that if you configure OSPF and its allowed to pick its own RID based on election you know the first choice is highest up/up loopback interface IP. So if you have made changes to your router such as adding more loopbacks for other functionality then a restart will cause that RID to change to another identifier and cause the LSAs to flood.

-David

[M02@rt37]

Hello @hfakoor222,

When you set a static RID for an OSPF router, you are essentially configuring the RID to remain constant, regardless of any internal factors. This means that even if the OSPF process is restarted or if there are any other events that would normally trigger an RID change, the RID remains the same. In contrast, if you don't set a static RID, the RID may change in certain situations, such as when the OSPF process is restarted or if there are conflicts in RID assignment.

By setting a static RID, you ensure that the RID doesn't change unless you manually modify the configuration. This consistency means that OSPF routers in the network don't have to generate new LSAs and flood them every time the RID changes due to a process restart or other factors. In OSPF, when an RID changes (such as due to a process restart), routers generate new Router LSAs (Type 1) and flood them throughout the OSPF domain. If you have a large OSPF network with many routers, this can lead to a significant number of LSAs being generated and flooded, consuming bandwidth and processing resources. By setting a static RID, you prevent these unnecessary LSA updates when the RID would have changed otherwise, reducing the overall number of LSAs in the network.