[AusNOG] VPLS OSPF question

[Mitchell Warden]

Hi Brad,

Some ideas below. There are a lot of considerations...

OSPF
- Will run fine on a VPLS service. I've done this with up to 30 or so sites in the past and it works well.
- 200 is a lot of sites - I would try to break it down to multiple smaller domains.
- 50 routers in an area isn't a big deal. It will depend on the CPU and the number of updates, but even 200 is unlikely to be a problem. 
- 200 neighbour adjacencies however might be a big deal (they're all on the same broadcast domain). I think 200 is too many.

BGP
- All of the routers could be in the same subnet so they would be able to reach each other directly without an IGP, if you build neighbors with interface addresses instead of loopbacks.
- You would need to use route reflectors to avoid having to mesh all 200 routers.
- I can't think of any reason BGP would reduce available bandwidth.
- BGP isn't really designed to be used internally, and I would try to avoid using it that way.
- BGP is probably better than OSPF if you can't reduce the size of the domain. It will be more scalable and probably more reliable.

Cheers.
Mitchell


----- Original Message -----
From: Brad McGinn
[mailto:the_xorach at yahoo.com]
To: ausnog at lists.ausnog.net
[mailto:ausnog at lists.ausnog.net]
Sent: Tue, 16 Apr 2013 17:14:02
+1000
Subject: [AusNOG] VPLS OSPF question


> Hi AusNog list,
 
Long time listener, first or second time caller.
 
I
> know this list is pretty specific to Service Providers so I'm hoping any of
> you who not only know carrier networks, but also have an insight into
> enterprise networks maybe able to help me to get a view (or even help
> understanding) of the pros and cons of running OSPF or BGP across a VPLS
> network.  
 
I respectfully ask your advice.  
 
I am an enterprise
> network engineer, not a service provider however I hope you don't hold that
> against me.  We run OSPF in our Data Centre and BGP into a MPLS network
> that all of our sites connect into.
 
My fairly basic understanding of VPLS
> is kind of like EoMPLS or even one big broadcast domain.  I assume any
> IGP could potentially work across it but some factors must be taken into
> consideration:  eg flapping sites, latency, reference bandwidth, DR/BDR
> placement, multicast transmission and so on.
 
So, with that in mind, I'm
> wondering the following:
-    would it be wise to run an IGP across a
> VPLS backbone with over 200 sites? or would BGP be better? or even something
> else?
-    if an IGP is the go, would one use OSPF?
-    if OSPF, do
> you think it would be wiser to run a separate OSPF process for the VPLS
> connected sites and a separate OSPF process for the DC?  and then
> redistribute or just summarise right there? (so as to protect the DC from
> OSPF recalculations when sites go up and down)
-    if BGP would be the
> go I'm wondering how one might go about it..  I know that all iBGP
> neighbours must have a route to the peering IP of all other iBGP routers so
> I would assume an IGP must be run anyway???
-    cisco say that
> anything more than 50 routers on an area is a bad idea, so if I have over
> 200 sites potentially on the VPLS, will OSPF cut it?
 
I guess i'm just
> trying to get my head around the different technology.  I'd love to keep
> the stability that BGP brings, but also would like to be able to make use
> of the bandwidth that VPLS gives.
 
Any hints or tips will be gratefully
> received and thank you for any help.  If you would like to keep from
> cluttering up subscriber's inboxes, please reply offlist.
 
Again, thanks
> for any help.
 
Regards,
 
Brad David