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OSPF Areas ID

Hi,

I need a confirmation about OSPF Areas...

Right now I've a topology using only one Area but it's not configured as a backbone Area: it's Area number is 5.

I need to interconnect Area 5 ONLY with a second one...this area should be configured as a Backbone Area or could it be every area number I want...

I remember that with 3 Areas I have to had a Backbone Area to interconnect them, but with only two Areas is it the same ?

Regards

2 REPLIES

Re: OSPF Areas ID

Hi,

in OSPF you need the ABR functionality to interconnect areas. The router(s) to become ABR needs an interface in area 0 (could be a loopback though) or a virtual link to area 0.

So in your case it would be best to configure the new area as area 0 (backbone area).

Hope this helps!

Regards, Martin

Re: OSPF Areas ID

Friend,

The ospf adjacency would be built eventhough you are not using area 0. (see attached debug adjacency output)

But as Martin has suggested, it would be better to go with area 0 for a single area as it will be needed in anyway when you plan to divide your OSPF domain into mutiple areas

*Mar 1 00:03:56.707: OSPF: End of hello processing

*Mar 1 00:04:03.699: OSPF: Send hello to 224.0.0.5 area 5 on FastEthernet0/0 fr

om 10.10.10.1

*Mar 1 00:04:03.751: OSPF: Rcv DBD from 2.2.2.2 on FastEthernet0/0 seq 0xFAC op

t 0x52 flag 0x7 len 32 mtu 1500 state INIT

*Mar 1 00:04:03.755: OSPF: 2 Way Communication to 2.2.2.2 on FastEthernet0/0, s

tate 2WAY

*Mar 1 00:04:03.755: OSPF: Neighbor change Event on interface FastEthernet0/0

*Mar 1 00:04:03.759: OSPF: DR/BDR election on FastEthernet0/0

*Mar 1 00:04:03.759: OSPF: Elect BDR 2.2.2.2

*Mar 1 00:04:03.759: OSPF: Elect DR 1.1.1.1

*Mar 1 00:04:03.763: DR: 1.1.1.1 (Id) BDR: 2.2.2.2 (Id)

*Mar 1 00:04:03.763: OSPF: Send DBD to 2.2.2.2 on FastEthernet0/0 seq 0xB3A opt

0x52 flag 0x7 len 32

*Mar 1 00:04:03.767: OSPF: NBR Negotiation Done. We are the SLAVE

*Mar 1 00:04:03.771: OSPF: Send DBD to 2.2.2.2 on FastEthernet0/0 seq 0xFAC opt

0x52 flag 0x2 len 52

*Mar 1 00:04:03.995: OSPF: Rcv hello from 2.2.2.2 area 5 from FastEthernet0/0 1

0.10.10.2

*Mar 1 00:04:03.999: OSPF: Neighbor change Event on interface FastEthernet0/0

*Mar 1 00:04:03.999: OSPF: DR/BDR election on FastEthernet0/0

*Mar 1 00:04:03.999: OSPF: Elect BDR 2.2.2.2

*Mar 1 00:04:04.003: OSPF: Elect DR 1.1.1.1

*Mar 1 00:04:04.003: DR: 1.1.1.1 (Id) BDR: 2.2.2.2 (Id)

*Mar 1 00:04:04.007: OSPF: Neighbor change Event on interface FastEthernet0/0

*Mar 1 00:04:04.007: OSPF: DR/BDR election on FastEthernet0/0

*Mar 1 00:04:04.007: OSPF: Elect BDR 2.2.2.2

*Mar 1 00:04:04.011: OSPF: Elect DR 1.1.1.1

*Mar 1 00:04:04.011: DR: 1.1.1.1 (Id) BDR: 2.2.2.2 (Id)

*Mar 1 00:04:04.011: OSPF: End of hello processing

*Mar 1 00:04:04.023: OSPF: Rcv DBD from 2.2.2.2 on FastEthernet0/0 seq 0xFAD op

t 0x52 flag 0x3 len 52 mtu 1500 state EXCHANGE

*Mar 1 00:04:04.027: OSPF: Send DBD to 2.2.2.2 on FastEthernet0/0 seq 0xFAD opt

0x52 flag 0x0 len 32

*Mar 1 00:04:04.139: OSPF: Rcv DBD from 2.2.2.2 on FastEthernet0/0 seq 0xFAE op

t 0x52 flag 0x1 len 32 mtu 1500 state EXCHANGE

*Mar 1 00:04:04.143: OSPF: Exchange Done with 2.2.2.2 on FastEthernet0/0

*Mar 1 00:04:04.143: OSPF: Send LS REQ to 2.2.2.2 length 12 LSA count 1

*Mar 1 00:04:04.147: OSPF: Send DBD to 2.2.2.2 on FastEthernet0/0 seq 0xFAE opt

0x52 flag 0x0 len 32

*Mar 1 00:04:04.231: OSPF: Rcv LS REQ from 2.2.2.2 on FastEthernet0/0 length 36

LSA count 1

*Mar 1 00:04:04.235: OSPF: Send UPD to 10.10.10.2 on FastEthernet0/0 length 40

LSA count 1

*Mar 1 00:04:04.403: OSPF: Rcv LS UPD from 2.2.2.2 on FastEthernet0/0 length 64

LSA count 1

*Mar 1 00:04:04.407: OSPF: Synchronized with 2.2.2.2 on FastEthernet0/0, state

FULL

*Mar 1 00:04:04.407: %OSPF-5-ADJCHG: Process 100, Nbr 2.2.2.2 on FastEthernet0/

0 from LOADING to FULL, Loading Done

HTH, rate if it does

Narayan

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