Could one router be configured as being in two OSPF areas same time?

[taolei]

I mean ,for example,Router B and C belongs to area B and C respectively,

and meanwhile,These two routers belong to backbone area also.Now,There

is another Router A, which is located on the border of area B,C. Then how

shall I configure the two interfaces of router A which connecting into Area B and C.

Thanks a lot!

[thisisshanky]

What do u mean by border of area B andC. You mean to say B and C are linked by router A ? Then u need to put interface of A connecting to router B in area B and interface of A connecting to C into area C.

[scottmac]

That would not be a valild OSPF configuration. All areas (except transition areas) connect to area zero, and only area zero.

A transition link is a tunnel through a non-zero area to connect to the zero area.

like (area 5)-(==area 3=====transition / tunnel======area 3==)-(area 0)

There is no "connection" in the transition area, the data is mearly passed along to to interface connecting to area zero.

The router could be connected between the two non-zero areas , it just has to be running a different routing protocol (and not OSPF at all). It would be a (seriously ugly) bad design, but you could do it.

Scott

[taolei]

thanks a lot.

I see what you mean,but I think my problem is quite complicated.

Please check the topo below.

A1 /[==]

Area 0 / [==]A2

B1 [==]/ | Area a

B2 [==] |

C1[==]

Area b C2 [==]

Maybe you are not quite clear yet,let me explain in more detail.

A,B and C are three sites of my network, A1 and B1 are the

backbone routers,which belong to the area 0,and meanwhile

as A2 and B2,they belong to the area a and area b respectively.

C1 and C2 belong to the area a.

Now there is a link between A1 and B1,the interfaces of these two routers

connecting this circuit are configured into area 0. But the problem is that this

link is not very reliable, so I want to do a backup between these two sites, but adding another link between A1 and B1 is pretty expensive,so I consider if I can put a link between B2 and C2,then there will be a alternate path connecting A2 and B2 as well,and more important is that will be more affordable.

Do you think I could do it? and if yes,how to?

[steven-dunn]

Router A will not route any inter area data as it is not an ABR so is effectively useless. Your design is not conforming to OSPF design. Router A should have a complete route table comprised of updates from routers B and C, but will not provide redundancy during failure.