LSA problem in Routing

[kthned]

Hi to All

I m preparing for BSCI 642-801 exam these days , and studying Cisco press book by Clare Gough

The problem iss

The book says that Five types of packets are used to build the routing tablefor the first time

1.Hello

2.Database Descriptor

3.Link State Request

4.Link State Update

5.Link State Ack

My question is "Where is LSA-Link State Advertisement"

Is it DAtabase Descriptor And Link State Update

or something else

Thanks in advance for ur answer

Syed Umair Ali

[Georg Pauwen · Accepted solution]

Hello Syed,

basically, LSA advertisement means simply that LSA packets (which can contain the five packet types you have mentioned) are being sent periodically between OSPF neighbors in order to keep the topology table updated and consistent throughout the OSPF domain.

Does that make sense ? Check the following documents which might clarify the concept:

What is OSPF ? (Scroll down to the ' Packet Format' section

http://www.pulsewan.com/data101/ospf_basics.htm

OSPF Neighbor States

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f0e.shtml

Regards,

GP

[suresh.krishnamurthy]

Hi all,

I am new to this Netpro. Iam not any professional.

My answer may be wrong. If so please correct me.

There are five types of OSPF packets.

1. Hello - Finds the neighbor & goes into 2way.

In case of Pt-to-Pt Networks it tries to become adjacent with it's neighbor with the help of DD Packets.

2. DD packets - It chooses a Master/Slave during Exstart state. During Exchange state exchanges "LSA headers" which are available in their database.

Both the routers prepare Requestlist(The list of LSAs which are latest/or not availbale in its database)

3. LS Request - LSA headers in the requestlist are sent to the neighboring router (to get the complete LSAs). The state is "Loading". Loading and Exchange can be parallel process reduce the convergence time.

4. LS Update - Requested updates are sent with the help of these pkts. These "LSAs" are stored in the OSPF Database.Now this router makes the state of other "FULL" SPF will be run locally to prepare the IP Forwarding table (Routing Table)

5. LS Ack pkt - Either implicit or explicit Acks are sent.

Now Mr. Syed I am going to answer your question.

1.During Exchange state a router exchanges "LSA headers" that are stored in it's OSPF Database.

2. OSPF Database is filled up when the router receives LS update pkt.

3.From the above argument I presume that "Link State Advertisement" means "Link State Update".

Others like

Hello pkt.- finds the neighbor,

DD pkt.- synchronise the database,

LS req. Pkt - asking for the LSA

LS Ack pkt. for acknowledging the receipt of LSA

are only helping the OSPF process to get the Updates.

Thanks & Regards

Krishnamurthy Suresh

[kthned]

Thanks GP(Sorry I dont know ur full name) and Suresh for ur help. Now I got the answer. specially GP ur 2nd Link is the best.

Thanks Again