Packet transmission in OSPF

[thangaRasu]

The LSRefreshtime is 30 minutes in OSPF as per rfc 2328, So the router LSA will start after this time(30 minutes). By using router lsa only the Link State Database will be updated. Suppose the datatransmission is started when it(router) is switched on. At this situation the packets will be dropped or any other solution? by using Link State Database only the routing table will be updated.

[antonio.guirado]

Hello,

I do not understand the exact question but notice that each LSA has a 30-min timer (it is not a global timer for all the LSA's). Besides, LSAs have a maximum age of 60 min before they are removed from LSDB. Only the LSAs learned by

Virtual links have a DNA (DoNotAge) option set and do not age out.

Regards

[Giuseppe Larosa]

Hello Thangarasu,

as Antonio has already noted the 30 min timer is individual of each LSA data structure, so there is no synchronization of LSA refresh, but you can consider a population of LSAs spread over the 30 minutes each with its own Refresh time.

I have done tests some years ago to measure the bandwidth use of OSPF as a function of the number of routes for the different types (internal inter area external).

I can confirm the spreading effects on refresh, each LSA is refreshed at a different time.

Then for efficiency reasons multiple LSAs can be flooded in the same packet but this is a different aspect

>> Suppose the datatransmission is started when it(router) is switched on. At this situation the packets will be dropped or any other solution?

When the router is started the OSPF process is starting too, the database is empty and the device does not take part in the LSA flooding process. So there is no issue at startup.

Hope to help

Giuseppe