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unwired9
Premium
join:2008-04-08
Algoma, WI

[Tech Ops] MPLS

I'm looking at migrating from mac-auth to pppoe - My OSS vendor recommended running mpls - I currenlty have an ospf network in place. Looking for your guys opinion on mpls and whether or not it is worth investigating further. I do not currently have a need for the vpn functionality that mpls would provide. My understanding is the switching the mpls would provide would be more efficient than routing the pppoe clients over ospf. I'm currently running Mikrotik routers with UBNT wireless equipment.


Inssomniak
The Glitch
Premium
join:2005-04-06
Cayuga, ON
kudos:2
Ill tell you what I use MPLS for.

I still use OSPF for route distribution.

I create VPLS tunnels from each PoP to a core router, bridge in the APs or what-have-you that are going to be customer interfaces to the VPLS tunnel, then a core router does all the PPPoE termination. I use bridge horizons to keep traffic from flowing back out of the core router.

Your L2MTU is important for MPLS networks.
You do not need to use MPLS for pppoe, ospf works for that, but if you want central termination, then MPLS is definitely an option to look at.
--
OptionsDSL Wireless Internet
»www.optionsdsl.ca

unwired9
Premium
join:2008-04-08
Algoma, WI
Is there an advantage to centrally locating your ppp termination - I was planning on terminating at each pop.


Inssomniak
The Glitch
Premium
join:2005-04-06
Cayuga, ON
kudos:2
said by unwired9:

Is there an advantage to centrally locating your ppp termination - I was planning on terminating at each pop.

I used to do that, hated it.
Wasted IP space, had to constantly reconfigure to add IP addresses (no big deal if you are using private space I guess). Radius config was a pain.

It was just a central place to manage stuff, keep all the hard work on a core (powerful) router.
--
OptionsDSL Wireless Internet
»www.optionsdsl.ca

unwired9
Premium
join:2008-04-08
Algoma, WI
Ok - IP Space is my reasoning for changing to pppoe - I can centrally manage the ip pool while keeping NAS server closer to the customers. I guess more specifically is there an advantage to running mpls vs routing public ip's with ospf. To implement I would have to replace all of the routers on my network. Just trying to figure out if its justified and if I would see an improvement over straight ospf routing or would it be a lot of work for little gain.


Inssomniak
The Glitch
Premium
join:2005-04-06
Cayuga, ON
kudos:2
Well unless you want to run VPLS VPN tunnels I wouldn't be switching.
Ospf won't degrade packet forwarding performance. It's just a route distribution protocol.

You don't really switch necessarily. I still use ospf alongside with mpls. You still need to have routes. MPLS works over current routing table wether its static or OSPF or BGP or whatever.
--
OptionsDSL Wireless Internet
»www.optionsdsl.ca


TomS_
Git-r-done
Premium,MVM
join:2002-07-19
London, UK
kudos:5

2 edits
reply to unwired9
MPLS isn't really a replacement for an IGP routing protocol like OSPF. Its more a complementary technology.

What was the exact benefit that your OSS vendor gave as a reason for adding MPLS to your network?

Like Inssomniak, I'll tell you what I used MPLS for in my previous job.

We used MPLS for L3VPNs to keep the management network for our WiMAX network "contained", as opposed to mixing it in with the management network for our POPs.

Along with this we also sold L3VPNs to some customers to link offices together, and we also did some pseudowire stuff to provide "a really long ethernet cable" to some specific customers.

said by unwired :

My understanding is the switching the mpls would provide would be more efficient than routing the pppoe clients over ospf.

Kind of. But it may not be noticeable with a small network. And you're still going to need to run an IGP anyway.

In BIG carrier networks, MPLS makes more sense for moving traffic through the very inner core of the network because its a much simpler method of switching packets compared to IP routing, and as a result, the very core devices can be really "simple" and move lots of data really quickly.

Also you dont really "route over OSPF". OSPF is just a protocol that talks to neighboring routers to share routing information that it uses to work out how to get from one part of a network to another. That information is populated in to the FIB of a router, and the router then forwards the traffic.

You could think of OSPF as like phoning a friend to ask what address you should write on an envelope to post a letter to them.

Routing would be the postal service then does the delivery, routing the letter through its facilities and delivering it to your friends mailbox by reading the address you have written and using that to determine how to route it.

MPLS could be thought of in a similar manner, but instead of writing an address, you stick a barcode that describes the destination on the letter instead. The postal service then very easily decodes the barcode to determine where to send the letter next. They can do this much quicker than trying to read the address you have written on the envelope, and as such equipment will be much simpler, and it will process more envelopes.

wvvawireless

join:2005-01-15
Rich Creek, VA
reply to unwired9
We are also looking at going to pppoe and debating central vs pop termination and using mpls.

I also like the idea of the central termination but have a question.

We have an ospf network with redundant back hauls on each end of the network. Currently half the traffic goes to one and the other half to the other. If anything fails all traffic moves to whats available. If I use mpls tunnels and a concentrator back to one side how can I have it switch to the other upon a failure?

unwired9
Premium
join:2008-04-08
Algoma, WI
reply to TomS_
So there would be a performance benefit to mpls - At what size would you look at implementing?


TomS_
Git-r-done
Premium,MVM
join:2002-07-19
London, UK
kudos:5
Maybe. But what Im getting at is that you probably wouldnt notice whatever benefits you might get out of it.

You can implement it at any size network, but where it becomes more beneficial is when you are routing traffic in the many, perhaps tens of gigabits/sec. And at that, when it is implemented in hardware as opposed to software.

And thats why Im interested as to why it was recommended to you.


TomS_
Git-r-done
Premium,MVM
join:2002-07-19
London, UK
kudos:5
reply to wvvawireless
MPLS typically switches over a single path when using LDP as your label protocol, and that usually follows the same path that your IGP thinks is the best way to route traffic around your network. So the short answer is yes, MPLS tunnels will automatically "switch" around failed links.

If you want to get really tricky you need to look at traffic engineering with things like RSVP. But even I havent really played with that.

If you dont mind statically assigning IPs to your customers (which is almost a requirement these days anyway with always on broadband) then you can still use localised termination, with the IP address assigned through RADIUS when the user authenticates. This way you still get the most efficient use of your IP space by not having to assign pools to each tower or BRAS, since your IGP will make sure the network knows how to route packets to each customer.

unwired9
Premium
join:2008-04-08
Algoma, WI
I'm not sure why it was suggested other than it's a really good way to do things. My original question to them was how to handle the ip pool within radius and have the nas servers at each pop. What I am currently testing is I have added one of my public /24 into the ospf networks - So I have a central pool of addresses so I don't necessarily have to assign statics and I shouldn't need to assign blocks to each pop. The radius server assigns and address from the pool and then ospf takes over and adds in a route for the address on that corresponding router. The one issue with this config is going to be the routing table size but I feel I'm a few thousand subscribers away from that being a problem.


TomS_
Git-r-done
Premium,MVM
join:2002-07-19
London, UK
kudos:5
said by unwired9:

The one issue with this config is going to be the routing table size but I feel I'm a few thousand subscribers away from that being a problem.

What sort of routers are you using? With a software based router (i.e. no hardware forwarding), routing table size should be limited only by how much RAM the box has.

If its a hardware based router, chances are it will support perhaps hundreds of thousands of FIB entries anyway.

There is also a RIB which is stored in RAM, and is used to populate the FIB. The RIB is usually much bigger than the FIB, since the RIB contains all copies of routes received, while the FIB contains only the ones needed to forward packets.

FIB = Forwarding Information Base
RIB = Routing Information Base

As a side note, the current Internet routing table at I think somewhere around 440,000 routes only consumes maybe 50MB of RAM on a Cisco router.


Inssomniak
The Glitch
Premium
join:2005-04-06
Cayuga, ON
kudos:2
reply to wvvawireless
said by wvvawireless:

We have an ospf network with redundant back hauls on each end of the network. Currently half the traffic goes to one and the other half to the other. If anything fails all traffic moves to whats available. If I use mpls tunnels and a concentrator back to one side how can I have it switch to the other upon a failure?

Yes just to add. It follows LDP. I have several redundant paths thru my network and it switches over just fine.
--
OptionsDSL Wireless Internet
»www.optionsdsl.ca

unwired9
Premium
join:2008-04-08
Algoma, WI
reply to TomS_
I have mostly RB50g or 493ah at each pop - Imagestream at the core. I believe at most I have seen my routers spike at 15% cpu and that is with Butch's QOS script running. I will have to relocate Butch's scripts moving forward but was struggling to see just where the benefit in mpls would come vs what I already have in place.

bairdmj

join:2009-12-30
reply to unwired9
If you centrally assign IP addresses via RADIUS (from one common, central pool), you will inject one host route (a /32) into your IGP's (OSPF) routing table for every client who connects. Furthermore, every time one of your clients disconnects/reconnects their PPPoE connection, an update to your routing table will occur. Each device that participates in OSPF on your network will will receive the "update" every time a PPPoE connection state changes.

If you choose to route a block of IPs to each PPPoE concentrator, it will be a bit more difficult to manage your IPs efficiently. But, you will be able to summarize the route for the block of IPs. This means that instead of having 253 /32 host-routes for each client in a /24, the router/concentrator would only announce one summary route (the /24) to the rest of your network. In addition, because you are summarizing the route, your routing table won't update each time a client connects/disconnects.


Inssomniak
The Glitch
Premium
join:2005-04-06
Cayuga, ON
kudos:2
said by bairdmj:

If you centrally assign IP addresses via RADIUS (from one common, central pool), you will inject one host route (a /32) into your IGP's (OSPF) routing table for every client who connects. Furthermore, every time one of your clients disconnects/reconnects their PPPoE connection, an update to your routing table will occur. Each device that participates in OSPF on your network will will receive the "update" every time a PPPoE connection state changes.

You can still filter this out no problem. I have a centrally assigned IP address setup from RADIUS and just block it in an "ospf-out" chain so all my other routers cant see it, they have no need to see it.
--
OptionsDSL Wireless Internet
»www.optionsdsl.ca


TomS_
Git-r-done
Premium,MVM
join:2002-07-19
London, UK
kudos:5
Yeah. Most likely you can have the router doing the termination announce a summary route in place of all of the host routes.

If youre terminating locally at each tower or in a non-centralised way, naturally you have little choice.

spectrumhead

join:2009-05-03
reply to Inssomniak
If you were running OSPF, why you were wasting IP space ?

It doesnt make any sense.


Inssomniak
The Glitch
Premium
join:2005-04-06
Cayuga, ON
kudos:2
said by spectrumhead:

If you were running OSPF, why you were wasting IP space ?

It doesnt make any sense.

I dont really remember if I was, I think the problem I was having is if 13 PPPoE concentrators were hitting the radius server at the same time (say after a large power blackout), the radius server would inadvertently assign the same IP address to 2-3 different customers. At least with it all on one concentrator it would reject the duplicate IP and try again, although I have not seen that in a long time (perhaps my radius/database server was too slow at the time).

Another reason I went with central concentrator was the ease of adding in other access sites, it was simple to just add an IP, turn on OSPF, MPLS, LDP and assign a VPLS tunnel ID, and bridge in my APs. Keeps CPU usage low, and configs simple..
--
OptionsDSL Wireless Internet
»www.optionsdsl.ca

spectrumhead

join:2009-05-03
Yes as I am currently thinking about doing the same, centralizing the PPPoE server with MPLS, but all this MPLS and VPLS stuff seems so complicated to me.