OSPF or BGP for MPLS network for WISP

RouterOS Forwarding Protocols
1

Hi Guys

I have been following the wiki’s regarding MPLS setups and I have a question:

What is the more robust routing protocol to use to distribute LDP packets in an MPLS network? ie OSPF or BGP?

Reason i’m asking is because our current OSPF network has a few links which change between states too often…ie from “full to Down” and i’m scared that this will affect the performance of the MPLS network

Thanks

2

what do you call ‘too often’? anyway, the performance of MPLS network should not be affected

3

about 4 times a day…would the OSPF changing state not affect a RSVP-TE tunnel?
thanks

4

MPLS works over current routing table, it do not depend on link state changes directly, so it’s not affected by appearing/disappearing of one (not significant?) route

5

oh I see what you mean…if I had a mesh network for example then it would be irrelavent if a link went down…ok thanks

Next question, if I may :slight_smile:

Lets say I have multiple highsites routed with MPLS but I have a single pppoe server near the internet breakout…All the clients would establish a pppoe session across the MPLS right? So now what would happen if a link went down? Would the pppoe sessions get dropped and then reconnected, assuming the primary LDP was over the link that went down? If yes, then how would one keep the pppoe session up during a re-route?

thanks

6

PPPoE sessions will not necessarily go down (provided that you do not add your PPPoE server and client interfaces directly to VPLS interfaces that will go down, but instead add PPPoE to bridge) - during “reroute” you will simply experience packet loss. It depends on your PPPoE config if that will terminate the session or not.

7

So if my VPLS is bridged to my AP ( on the interface that the stations connect to) and the stations dial the pppoe..In theory would the sessions stay up? granted there will be some packet loss

8

In general yes, as long as packet loss will not cause connections to get terminated, but that is only one part of the story - you also have to add PPPoE server on bridge interface and add VPLS interfaces (“the other ends” so to say) as ports to it, so that PPPoE server does not terminate connections because it looses interface it is added to.

9

ahh yes that makes sense…

I’m assuming that I should be using “split horizon” on all the VPLS ports that are added to the bridge? Otherwise each pppoe connection attempt would flood the network with broadcast packets…am I correct?

10

Yes, you are correct, in order to limit unnecessary broadcasting you should use either split horizon feature or bridge firewall.

11

Hi MPLSGUY

Well I got my 1st lab setup up and running and all is going well…VPLS works like a charm, thanks

1 last question regarding vrf’s:

Can I use OSPF to distribute the vrfs along the mpls cloud or must I use BGP? All the example’s i’ve read use BGP but none use OSPF

12

If you mean distributing routes installed in VFRs between PE routers, then yes, you must use BGP.

13

thanks

I’m having difficulting getting BGP to work, OSPF for MPLS + VPLS worked fine

Can I use OSPF between the all the MPLS routers to distribute the LDP’s and then BGP between just the PE routers for specific vrfs? or must I choose BGP or OSPF?

I hope i’m making sense

14

To clarify: you must use some IGP (RIP, OSPF or even static routing) to ensure end-to-end connectivity between PE routers. Then LDP distributes MPLS labels for existing routes. Note that OSPF (in case you use it) has nothing to do with MPLS - it simply distributes routes. MPLS switching along existing routes is ensured by LDP.

BGP is necessary to exchange routes in VRFs (so called VPNv4 routes) between PEs. BGP is required only between PEs.

15

thanks, makes more sense now

Regarding the CE-PE link for vrf’s…Should I use OSPF as the CE-PE routing protocol http://wiki.mikrotik.com/wiki/OSPF_as_PE-CE_routing_protocol

or something like this:

/ip route vrf add disabled=no routing-mark=cust-one route-distinguisher=1.1.1.1:111
export-route-targets=1.1.1.1:111 import-route-targets=1.1.1.1:111 interfaces=ether1
/routing bgp instance set default as=65000
/routing bgp instance vrf add instance=default routing-mark=cust-one redistribute-connected=yes
/routing bgp peer add remote-address=10.5.5.3 remote-as=65000 address-families=vpnv4
update-source=lobridge

Taken from here: http://wiki.mikrotik.com/wiki/Virtual_Routing_and_Forwarding.

I want to use the more stable option

16

You can use OSPF or you can use static routing - depends on what are the requirements and your preferences. If your policy is to allow your customer to introduce new networks and distribute routes across your core to other sites of that customer, then I guess you should use OSPF so you do not have to configure routing every time your customer changes something. If your customer routing is as simple as single net connected to your PE routers at multiple sites, then you do not need static routing.

17

thanks mplsguy

My customer needs are pretty simple so static routing should do the trick…

My lab test only had 1 CE router per PE so it was easy enough to specify the “interface”. What happens when I have ±30 customers connecting to the same sector? My gut feeling would be to create a unique vlan from the CPE <==> AP and then use that as the interface? Is there an easier way?

18

It is mandatory to have separate CE-PE interface in order to use multiple VRFs. There are multiple ways to achieve this (though none of them will probably be as easy as you would like) - VLANs (like you suggest), separate WDS interface for every customer (in case you use RouterOS on client side as well - I think this would be the preferred way because you would also eliminate broadcasting/multicasting in wireless), or any other way of tunneling.

If CPEs are in your control, you can also consider making CPE routers to be PE routers (and simply MPLS switch at the AP) - this would be the most efficient solution performance wise.

19

Thanks again mplsguy

I tried the WDS setup before and it gave me issues with nstreme so I’m going to try the CPE being part of the MPLS cloud…

All our CPE’s are mikrotik and we have control, so am I correct in assuming that I would only use BGP on the CPE’s (for vrf’s) instead of on the highsites? This would simplify things quite a bit for the backbone network.

EDIT: would having all these additional MPLS routers (CPE’s) affect performace of the MPLS network? CPE’s are normally lower spec routerboards than the highsites

20

You must use station-wds mode on client in order to have WDS links in nstreme network.

All our CPE’s are mikrotik and we have control, so am I correct in assuming that I would only use BGP on the CPE’s (for vrf’s) instead of on the highsites? This would simplify things quite a bit for the backbone network.

Yes.

EDIT: would having all these additional MPLS routers (CPE’s) affect performace of the MPLS network? CPE’s are normally lower spec routerboards than the highsites

I do not think that moving MPLS ingress point to CPE would significantly degrade its performance compared to regular routing (taking into account that it is transmitting over wireless, not over gigabit ethernet - so it should not be at its max load anyway). I would even say that this would give overall performance benefits, because: 1 - you will eliminate one hop that does IP routing (AP), 2 - you will distribute the load of “introducing” labels across multiple CPE routers where before it was done by single AP.