Re: [AFMUG] PPPoE and /32's

[Jesse DuPont]

Yeah, those are the only two ways to do it using only OSPF:

1. Route Filters
2. OSPF non-backbone area with PPPoE network in that area and an area-range set (to aggregate)

Jesse DuPont

Network Architect
email: jesse.dup...@celeritycorp.net
Celerity Networks LLC

Celerity Broadband LLC
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On 1/2/20 1:46 PM, Ken Hohhof wrote:

It’s not that complex, unless I’m missing something.

 

On Cisco routers we route the x.x.x.x/24 (or whatever netblock is assigned to that PPPoE NAS) to Null0.

 

On Mikrotik we use add a route filter to chain ospf-out with matcher parameters prefix=x.x.x.x/24 and prefix length=32, with action=""  We also set up a static blackhole route for the netblock but that’s so traffic to unassigned pool addresses doesn’t go round and round, it doesn’t stop Mikrotik from advertising /32 routes via OSPF unless you also do the router filter.

 

There might be better or more elegant ways to accomplish it, but those seem to do the trick.

 

 

From: AF <af-boun...@af.afmug.com> On Behalf Of Adam Moffett
Sent: Thursday, January 2, 2020 12:26 PM
To: af@af.afmug.com
Subject: Re: [AFMUG] PPPoE and /32's

 

Good point. 

On 1/2/2020 1:22 PM, Jesse DuPont wrote:

How are you getting around it doing a /32 for each PPPoE session right now? Even if you don't do redistribute connected, but have the whole, let's say, /24 in OSPF-Networks, there will be an entry for each /32 in all the route tables regardless because OSPF uses the mask present on the link (which is a /32). So how are you advertising the larger network today and not getting all the /32's? Route Filters?

The only way I know to get OSPF to actually summarize it for you is to put it in it's own area (i.e. the PPPoE stub area), add the network prefix to the PPPoE area (not the backbone area), and specify the aggregation network in OSPF-Area Ranges.

Like Matthew, I use iBGP to announce those and not OSPF.

Jesse DuPont

Network Architect
email: jesse.dup...@celeritycorp.net
Celerity Networks LLC

Celerity Broadband LLC
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On 1/2/20 11:09 AM, Adam Moffett wrote:

If you redistribute connected routes on a PPPoE server you get a route for every /32 and that's undesirable.

My solution currently is to NOT redistribute connected and instead just advertise the larger network which will encompass all the /32's.

I read a presentation suggesting to use an OSPF stub area for the PPPoE concentrator.  Is there a reason I'd want to use a stub area instead of specifying the network to distribute?

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