Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements
Webcast-Catalyst9k
New Member

OSPF:How many ABR's in one area

Hi , I'd like to ask you how many ABR's are recommended in one area.

I have about 4 ABR's , and everyone is connected into one or more C network, for example:

10.1.1.0

10.1.2.0

10.1.3.0 ....

Should I summarize the routes on every router with 10.1.0.0/16 ?

thank you

pet

5 REPLIES
New Member

Re: OSPF:How many ABR's in one area

It depend off design strategy, size of area, caliber of the routers.
You can summarize on every router

Can i see more of data  (topology, model of routers)

Sergey

New Member

Re: OSPF:How many ABR's in one area

thanks for an aswer.

i have 3 routers 1841, and one 1721

one routers has 4 subnets: 10.1.1.0,10.1.2.0,10.1.3.0,10.1.4.0

another routers  have one or two subnets ,in the style of: 10.1.10.0,10.1.11.0 , and so on

All subnets have the same area

All routers have also few tunnels uinto area 0 ( HeadQuater )

Routers are located in the different locations of the couontry, connected with gre ipsec tunnels

All are the ABR's

The questoin is if i should set the summarizing on all of them to 10.1.0.0/16 ?

thanks

Hall of Fame Super Blue

Re: OSPF:How many ABR's in one area

peter_jevos wrote:

thanks for an aswer.

i have 3 routers 1841, and one 1721

one routers has 4 subnets: 10.1.1.0,10.1.2.0,10.1.3.0,10.1.4.0

another routers  have one or two subnets ,in the style of: 10.1.10.0,10.1.11.0 , and so on

All subnets have the same area

All routers have also few tunnels uinto area 0 ( HeadQuater )

Routers are located in the different locations of the couontry, connected with gre ipsec tunnels

All are the ABR's

The questoin is if i should set the summarizing on all of them to 10.1.0.0/16 ?

thanks

Peter

If the routers are in different locations and they all connect back to area 0 then you can't summarise to 10.1.0.0/16 on all the routers because then you will have multiple routes to the 10.1.0.0/16 network with no way of knowing which one is the right one for a particular 10.1.x.0 subnet.  So you will have to advertise the individual subnets or possible summarise but not to 10.1.0.0/16 ie. you will have to be much more specific in how you summarise each sites 10.1.x.0 subnets.

Edit - can you clarify. The routers are all in the same area and they are in different parts of the country. Are they interconnected with each other or only connected via GRE tunnels to area 0 ?

Jon

New Member

Re: OSPF:How many ABR's in one area

Than you for your aswer

it makes sense, i will use more specific subnet with the subnet mask

And what about the number of ABR/s per one area ?

Is there any recommendation ?

Another question regarding OSPF.

We have 2 routers as ABR's per area that are connected to the one subnet (e.g. 10.1.1.0 - area 1)

Those two routers have different  ISP each with the tunnels to the area 0

Subnet 10.1.1.0 has one gateway, on the router R1 with 10.1.1.254

How to affect OSPF processes on both routers, that R1 will forward the packets to R2 if it has better costs to the destination ?

Routers are connected only through ethernet segment in area 1.

Because from the OSPF rules, if packet comes to the R1, it sends the packet out of the area1 to the area0, even the R2 has the better cost

One possibility is to create virtual link, another one is to create the tunnel between R! and R2 through area0

Do you know about the others ?

thanks

New Member

Re: OSPF:How many ABR's in one area

Dear Jon

thank you for your answer.

Yes , the routers arein the same area with gre tunnels to the headquater ( data center )  in area 0,

there're interconnected also through gre tunels in the their area ( with better cost )

And that's the problem with summarization.

cause as i told you before, one of them keeps 4 C subnets, another ones per C subnets and so on

therefore i cannot summarize on B subnet, e.g. 10.1.0.0/16

thank you for your answer

985
Views
0
Helpful
5
Replies
CreatePlease to create content