OSPF Multi-access network

eng_ahmedas

Hi all
How r u ?? I wish u r all in a good health.I have 2 questions about ospf and i wish u could help me understanding it.

The first question: In multi-access networks, does hello packets exchanged only between all DRother routers or between DRother routers and DR only????

The second question: In multi-access networks ,In the discovering routes proccess of OSPF, does DBD packet , LSR , LSU and LSAck messages exchanged only between DRother routers or between DRother routers and DR only ???
Thanks in advance
Bye

Ching01

The first question: In multi-access networks, does hello packets exchanged only between all DRother routers or between DRother routers and DR only????

Regading to your 1st question:

In multi-access (like Ethernet ) broadcast network the DRother will form adjacency to DR and BDR. BDR is a back up only it only accept updates and not sending updates. DR is the one responsible for sending updates to its peer or neighbors(DROTHER).

The use of DR and BDR in the multi-access environment is to eliminate routing loops and routes that can be problems in your network just search on the cisoc website. So DRother sends a multicast of 255.0.0.6 to the DR and BDR while DR will send multicast 255.0.0.5 to all DRother if there is any changes on the network.

About your second question read about how DROTHER form adjacency to the DR. If I could remember the first process is down, init, 2way, exstart, exchange, load, full.
So again the DRothers has no idea about the DROTHERs it only know the DR and BDR and BDR is optional meaning you can have BDR or DR.

One more thing in a NBMA networks an attempt is included in the process.

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BubbaJ

Ching01 wrote:

So again the DRothers has no idea about the DROTHERs it only know the DR and BDR and BDR is optional meaning you can have BDR or DR.

Actually, all the routers send Hellos to the AllOSPFRouters Multicast address (224.0.0.5) and know about all the other routers. They only form adjacencies and exchange link information with the DR and BDR, but that doesn't mean that they don't know about the other routers. If you do show ip ospf neighbor on a DROther, you will still see all the routers listed as neighbors.

This is necessary in the event of a failure of the DR or BDR so that an election can take place.