OSPF proccess
Hi all,
Im just about to start the CCNP route and i just want to nail down some basics before i start reading up on OSPF. i was looking at my CCNA notes, and Ive wrote the following about the OSPF process:
1. Each router is given a router ID, (this acts as there name on the network so everyone knows who everyone is).
2. The routers send out hellos on the interface it is configured for and if attributes match they for an adjanceny
3. A DR and BDR is then selected, per network segment using the router ID as a judgement if no manual priority is configured.
4. All routers calculate the shortest path to a destination and poulate there routing tables which are sent to the DR to be flooded out.
5. Then if there is a change to the network, the router will send the LSA to the DR and BDR on a multicast address 224.0.0.6 and then the DR will send out this information to the other routers on teh shared segement to multicast 224.0.0.5
I understand the whole DR and BDR election etc... Im just wondering if the following is the correct order for OSPF? im particularly worried about understand at what stage the DR and BDR is elected per segment?
Thanks in advance
Dan
Im just about to start the CCNP route and i just want to nail down some basics before i start reading up on OSPF. i was looking at my CCNA notes, and Ive wrote the following about the OSPF process:
1. Each router is given a router ID, (this acts as there name on the network so everyone knows who everyone is).
2. The routers send out hellos on the interface it is configured for and if attributes match they for an adjanceny
3. A DR and BDR is then selected, per network segment using the router ID as a judgement if no manual priority is configured.
4. All routers calculate the shortest path to a destination and poulate there routing tables which are sent to the DR to be flooded out.
5. Then if there is a change to the network, the router will send the LSA to the DR and BDR on a multicast address 224.0.0.6 and then the DR will send out this information to the other routers on teh shared segement to multicast 224.0.0.5
I understand the whole DR and BDR election etc... Im just wondering if the following is the correct order for OSPF? im particularly worried about understand at what stage the DR and BDR is elected per segment?
Thanks in advance
Dan
Comments
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networker050184
Mod Posts: 11,962 Mod
One thing to keep in mind. A DR/BDR is only elected on a multi access segment.
For number 4 that is not how a link state protocol works. That would be how a distance vector protocol works. Link state routers send their links with the associated cost. They do not calculate routes and send that on.
The DR election is done during the 2-Way state of the neighbor adjacency process.An expert is a man who has made all the mistakes which can be made. -
Dieg0M
Member Posts: 861
One thing to keep in mind. A DR/BDR is only elected on a multi access segment.
Incorrect, a DR/BDR will also be elected on a point-to-point link aslong as the OSPF interface configuration is not defined as such.Follow my CCDE journey at www.routingnull0.com -
networker050184
Mod Posts: 11,962 Mod
That is not true. If you connect two routers together on a point-to-point serial link, with no manual configuration, a DR/BDR election will not occur. If it is an ethernet segment then you are correct. Ethernet is by definition multi access though.An expert is a man who has made all the mistakes which can be made.
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MickQ
Member Posts: 628 ■■■■□□□□□□
I'm with networker on this one; multi access (not just broadcast, Danmoh) networks and the interface state machine. Point of (B)DR being to reduce LSA traffic volumes.
Distance vector: routing by rumour - based off neighbours' hearsay.
Link state: has to have the full topology and each L3 device calculates its own "paths".