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OSPF Summarization within Area 0

 
 
ciscortp@hotmail.com
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      05-27-2006
Is it possible to use the area range command to summarize routes if you
only have area 0. For example if I have area 0 with the subnets
10.0.0.0 /26 and 10.0.0.64 /26. Can I perform the following:

area 0 range 10.0.0.0 255.255.254.0

What will this cause? Is this legal? Keep in mind that Area 0 is the
only area that exists.

Thanks.

 
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stephen
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      05-27-2006
<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
> Is it possible to use the area range command to summarize routes if you
> only have area 0. For example if I have area 0 with the subnets
> 10.0.0.0 /26 and 10.0.0.64 /26. Can I perform the following:
>
> area 0 range 10.0.0.0 255.255.254.0
>
> What will this cause? Is this legal? Keep in mind that Area 0 is the
> only area that exists.


it shouldnt have any effect (if the router even allows you to configure it).
Summaries are only used on ABRs and only affect the routes propagated across
an area boundary.

1 possible workaround is not to set up OSPF on those subnets and summarise
the routes during redistribution into OSPF.
- the summary is then an external rather than an internal summary (so
handling is different in some ways)
- only useful if 1 or more routers are connected to the set of subnets,
statics etc.
- not feasible if 1 or more of the subnets are links between routers where
you need OSPF adjacencies.
>
> Thanks.
>

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http://www.velocityreviews.com/forums/(E-Mail Removed) - replace xyz with ntl


 
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ciscortp@hotmail.com
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      05-27-2006
The challenge is that There are Mainframes that Are forming Ospf
Adjacencies with our routers, but the mainframes are generating Virtual
IPs (/32 host routes That don't exist on any links to the manframe).
We do not want to advertise all of these host routes so we would like
to summarize them. The problem is that we must use only area 0.
Another solution is to make the Mainframe their own stub area, then
perform the summarization into area 0, but this is not an option for
us. Please see below

Virtual IP
addresses===1.1.1.X/32====Mainframe-2.2.2.1/30====2.2.2.2/30-Router1

>From my drawing all devices are in ospf area 0. An adjacency is

formed between the Mainframe and the Router on the 2.2.2.0/30 subnet.
The 1.1.1.X/32 (Virtual addresses) routes are going to originate from
behind the Mainframe. Any way to summarize the 1.1.1.X/32's into a
/24 using OSPF

 
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stephen
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      05-27-2006
<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
> The challenge is that There are Mainframes that Are forming Ospf
> Adjacencies with our routers, but the mainframes are generating Virtual
> IPs (/32 host routes That don't exist on any links to the manframe).
> We do not want to advertise all of these host routes so we would like
> to summarize them. The problem is that we must use only area 0.
> Another solution is to make the Mainframe their own stub area, then
> perform the summarization into area 0, but this is not an option for
> us. Please see below
>
> Virtual IP
> addresses===1.1.1.X/32====Mainframe-2.2.2.1/30====2.2.2.2/30-Router1
>
> >From my drawing all devices are in ospf area 0. An adjacency is

> formed between the Mainframe and the Router on the 2.2.2.0/30 subnet.
> The 1.1.1.X/32 (Virtual addresses) routes are going to originate from
> behind the Mainframe. Any way to summarize the 1.1.1.X/32's into a
> /24 using OSPF


the only thing i can suggest is having 2 separate OSPF regions, and
summarising between them.

if the network design allows it, i would have 1 router connected to the
mainframe, and 1 to the main OSPF network, then run BGP between them (or
pairs if you need more resilience)

in theory you can run 2 (or more) OSPF processes on 1 router, and
redistribute.
however - it seems to be "bargepole" technology last time i looked - i.e.
lots of suggestions scattered aorund Cisco docs that says this is not
recommended etc.

good luck
>

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(E-Mail Removed) - replace xyz with ntl


 
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Merv
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      05-27-2006
If you do not want or need /32 from the mainframe then have the system
programmers reconfigure OMPROUTED accordingly.

They may have configured VIPA's, however, if you only have a single
mainframe these do not need to be broadcast into area 0. If you have
redundant mainframes that require the use of VIPA's because the VIPA
host routes will be announced over different links into area 0 then do
not summarize.

 
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