[Series of OSPF] Episode 5 How a router configured with OSPF rebuild topology based on LSDB Highlighted

Created Nov 30, 2018 18:31:19Latest reply Dec 18, 2018 15:28:56 386 17 2 3

In the previous four episodes, we introduced how the OSPF establish adjacency relationship and exchange its own LSDB with other routers, finally, every routers in the same area maintains the same LSDB. Routers can rebuild the topology and caculated the route path based on LSAs kept in the LSDB. 

First of all, let's talk about how the router rebuild the topology by the router-LSAs kept in the LSDB.

Topology as below:
topology

check LSDB on the router ar2 

lsdb_router


as the LSDB describe, two areas contained on router ar2.
check router-LSA in area 0 one by one

router-lsa-1-a0

picture above shows that a router-LSA with link-state ID 2.2.2.2, it is the RID of the router which generates this router-LSA. link count means how many links has connected to this router. As we talked about in episode 4, in router-LSA, if the type of the link is TransNet, link ID is the interface IP address of the DR, Data is the interface IP address which connects to this TransNet. In the picture above, a router with RID 2.2.2.2 connects three network segment, two TransNets and one Virtual. Link ID: 10.1.12.2, Data: 10.1.12.2, link type: TransNet, these three data points indicate that a router connects to transport network through an interface with IP address 10.1.12.2, in this network, the IP address of the interface which belongs to the DR is 10.1.12.2, as shown below.
PIC1

In this way, we can draw the rest of the router based on the router-LSAs as below.

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Combine the above topology results, we can get a topology rebuilt by the LSDB on the router shows as below.

rebuilt topology based on the LSDB on the router

when all the OSPF routers rebuild the topogoly based on their own LSDB, the topology of the entire OSPF network is completely reproduced.


In the next episode, we will introduce the SPF algorithm and how the OSPF generate the route path based on the LSDB 


 





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liwaye     Created Dec 03, 2018 09:27:13 Helpful(0) Helpful(0)

its really helpful to understanding OSPF protocol, marked all and hope you keep writing
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Jessicanaquin     Created Dec 04, 2018 13:56:06 Helpful(0) Helpful(0)

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Hawasli     Created Dec 12, 2018 00:03:44 Helpful(0) Helpful(0)

Good
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EdenHazard10     Created Dec 12, 2018 02:02:44 Helpful(0) Helpful(0)

Need more tools
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jomana     Created Dec 12, 2018 02:13:37 Helpful(0) Helpful(0)

It's good
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jomos     Created Dec 12, 2018 15:18:06 Helpful(0) Helpful(0)

Very good
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jomana     Created Dec 12, 2018 15:24:55 Helpful(0) Helpful(0)

Need more information
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Hawasli     Created Dec 13, 2018 01:10:07 Helpful(0) Helpful(0)

Its hard
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EdenHazard10     Created Dec 13, 2018 23:44:39 Helpful(0) Helpful(0)

Its hard
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