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natanielklug
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OSPF area range in another router

Fri Aug 16, 2013 9:18 pm

Hello all,

I am trying to setup an enviroment and it's getting some trouble to understand a simple concept: area range. Let me show what is the scenario:

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So as you can see I have a bunch of PPPoE NAS Concentrator wich redistributes a lot of /32 IPs. I can't summarize those IP ranges inside the NASes because they are redundant and a customer can connect in one of them with an IP (for example) 192.168.0.10/32 and another client, in another NAS, with de IP 192.168.0.11/32.

But the problem is my routing table is growing too fast over Router02 and Router03 and it's causing an abnormal usage of CPU and Memory on those routers. I tried to set a filter but the problem is still there because Router02/03 are still getting the router, they are only not installing them.

So, all my network runs over backbone area. My question is: how can I reduce the number of routes going to Router02/03?
---
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José Nataniel Centeno Klug
Operation Manager Certto Telecom
+55 45 3333 2135 | www.certto.com.br
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CelticComms
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Re: OSPF area range in another router

Sat Aug 17, 2013 10:37 pm

A couple of things are not fully clear from the diagram. Could you let us know:

Which area numbers each router is in including Router 01.
Whether or not the NAS devices are talking OSPF and if so which area numbers they are in.

It sounds as if area ranges could help. They allow summarisation of a specific "range" of IP numbers. That summarisation can occur on an ABR (or ASBR).

Perhaps let us know what you have tried and what didn't work.
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natanielklug
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Re: OSPF area range in another router

Sun Aug 18, 2013 3:31 am

Hello Celtic,
A couple of things are not fully clear from the diagram. Could you let us know:
Which area numbers each router is in including Router 01.
In that diagram Border, PPPoE NAS and Router01 are talking OSPF using backbone area (0.0.0.0).

Router02 is talking OSPF with Router01 on backbone area (0.0.0.0) and it's conecting another area called Router2 (0.0.0.2).
Router03 is talking OSPF with Router01 on backbone area (0.0.0.0) and it's conecting another area called Router3 (0.0.0.3).
Whether or not the NAS devices are talking OSPF and if so which area numbers they are in.
They talk OSPF and they run over backbone area (0.0.0.0) and the PPPoE sessions are over a PPPoE specific area (0.0.0.255).
It sounds as if area ranges could help. They allow summarisation of a specific "range" of IP numbers. That summarisation can occur on an ABR (or ASBR).
Perhaps let us know what you have tried and what didn't work.
Area Range I already tried on NASes but I can have several PPPoE sessions over the same IP Range in different NAS so, I was not able to setup Area Range properly.

Only thing I tried was filter on Router02 and Router03 but it was not a good move.
---
Best regards,

José Nataniel Centeno Klug
Operation Manager Certto Telecom
+55 45 3333 2135 | www.certto.com.br
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Re: OSPF area range in another router

Sun Aug 18, 2013 6:18 pm

One thing you might consider to alleviate the issue, is to stop routing at the edge and backhaul the customers at each location in a VLAN via VPLS to the PPPoE NAS/BRAS. That way you can maintain small routing tables at the edge for MPLS/OSPF and put the larger /32 table in a core router/NAS that has more memory and capacity.

Using MPLS to backhaul VLANs from the last mile is very common in large Telco/DSL networks with PPPoE so that you don't need large route tables at every site.
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Re: OSPF area range in another router

Sun Aug 18, 2013 9:37 pm

Is there anything to stop you placing the NAS units themselves into the PPPoE OSPF area? If you can do then Router01 becomes the ABR between Area 0 and PPPoE. You can then use Area Range on Router01 to summarize the 192.168.0.X/32 routes coming from the PPPoE area into (e.g.) a /24. At that point Router01 will still have the individual /32 entries pointing to the relevant NAT but Router02 and Router03 will only see a (e.g.) /24 route.
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Re: OSPF area range in another router

Mon Aug 19, 2013 4:33 pm

One thing you might consider to alleviate the issue, is to stop routing at the edge and backhaul the customers at each location in a VLAN via VPLS to the PPPoE NAS/BRAS. That way you can maintain small routing tables at the edge for MPLS/OSPF and put the larger /32 table in a core router/NAS that has more memory and capacity.

Using MPLS to backhaul VLANs from the last mile is very common in large Telco/DSL networks with PPPoE so that you don't need large route tables at every site.
Thank you for your answer. You put some new conecpts to my attention and I am in the way to understand them. As you say I could bring my customers do NAS using VPLS. We are using EoIP for this and in the edge I do not need the routing table of the PPPoE customers. That's the point: how can I not have this at the edge of the network?

The layout I put here is just a small part. We have more than 900 devices in our routing space and at least 9000 routes and almost 8000 are PPPoE Sessions. Most of the orther routes could be small at some point. For example there are several /30 networks over 172.16.0.0/20 and some points in the network they should only see 172.16.0.0/20 and not every single /30. This is where my knowledge of routing is making me ask.

I will learn more about VPLS/MPLS and see how to use this inside my network. Thank you.
Is there anything to stop you placing the NAS units themselves into the PPPoE OSPF area? If you can do then Router01 becomes the ABR between Area 0 and PPPoE. You can then use Area Range on Router01 to summarize the 192.168.0.X/32 routes coming from the PPPoE area into (e.g.) a /24. At that point Router01 will still have the individual /32 entries pointing to the relevant NAT but Router02 and Router03 will only see a (e.g.) /24 route.
Celtic,

I don't know if what I done is the right thing. So let's me explain:

Router01 is connected to Router02 and Router03 using backbone area (0.0.0.0) and Router01-02-03 are receiving all /32. So I setup on Router01 an AreaRange for the network 192.168.0.0/24 (considering all my PPPoE Sessions are 192.168.0.0/32) over the area backbone. Router02 and Router03 are still receiving all /32.

So, for me to set Router01 as an ABR it needs to connect to Router02 and Router03 throu another area? So if my BorderRouter is distributing default routes it will still do? For this layout I will need to make some arrangements in my IP Address spaces so every area get only IPs from that area. Is this correct?
---
Best regards,

José Nataniel Centeno Klug
Operation Manager Certto Telecom
+55 45 3333 2135 | www.certto.com.br
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CelticComms
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Re: OSPF area range in another router

Mon Aug 19, 2013 5:04 pm

Sounds as if you were headed in the right direction. Is it possible to have a look at the system remotely? Contact me via email if so.
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