OSPF - Subnet Summarization to Reduce Routing Table Size

[LarW63]

Hi,

We have Fortigates (FortiOS 5.4.5) running at multiple locations using site-site VPNs and OSPF dynamic routing. Also, at each location, there are multiple subnets (interfaces) configured.

When we look at the routing table it's getting excessively large. Fortunately, each location has a uniform IP assignment, which would allow all of the subnets to be summarized into one larger network.

I've tried several different combinations of CLI: Config Router OSPF -> Config Area -> Config Range -> Set Prefix and Set Substitute but it seems that I get mixed results. I'm also having trouble finding documentation detailing how to summarize several smaller subnets into one larger network.

Does anyone have a link to documentation showing how this is supposed to be configured? Or, does anyone have input on the following questions?

- For prefixes, is this an exact match? Or, is this an equal to or greater than mask length match? - I assume that substitute and substitute-status defines and enables/disables the summarizing of addresses matched by the prefix. Is this assumption correct? - What's the purpose of advertise enable/disable?

If there is a alternate/better way to achieve summarization, I'd be interested in that too.

Thanks your for time.

Larry

[LarW63]

Hi,

One further aspect...  The VPNs between the Fortigates are in Area 0.0.0.0 while the subnets at each Fortigate are in separate areas, making each Fortigate an ABR (Area Border Router).

Larry

[emnoc]

Will if the   fortigates at the spoke are true ABR than route-summary should be a ease.

You should look at the area  range command, the fortigate wan routing guide has numerous examples on how to deploy  dynamic-routing

question you should ask and review

[ul]

Do you  need inter-area routing[/ul][ul]

can a stub work[/ul][ul]

Are your spokes a ABR only or ABR+ASBR  and  have numerous redistributes  TYPE-5 LSAs[/ul]

Only you know those answers, based on those answer you can optimized the OSPF routing

Ken

[LarW63]

Hi,

After further experimentation, the following achieves the summarization I require.

config router ospf set router-id 172.19.255.34 config area edit 0.0.0.0 next edit 172.18.248.0 config range edit 1 set prefix 172.18.248.0 255.255.255.0 next end next end

The single "set prefix" command is all that is required.

I just wish this was documented better as it would have saved time.

Larry

[chilun]

Late reply about a year.

You can use "summary-address".

config router ospf

config summary-address

edit 1

set prefix 172.18.248.0 255.255.255.0

next

end

[hubertzw]

@chilun  there are two different types of summarization:

- config range is for ABR

- config summary-address is for ASBR

So 'config summary-address' doesn't work on ABR