Creating a tunnel over BGP loadbalanced paths

Answered Question
Feb 2nd, 2007

Hi,

We hired a 4 mbps link between our plant at Brazil and the plant at Argentina. At remote side it was delivered a full 4 Mbps channel, but at Brasil 02x 02 mbps links and that's when the problem shows up. Provider is trying to use BGP, so I'd like somebody cleared to why this should be the best solution, and what is the danger of this traffic be propagated at our OSPF network.

I thanks if somebody please help me.

Alex

I have this problem too.
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Correct Answer by dknov about 9 years 7 months ago

Hi Alex,

I would assume that this is NOT point-to-point link between your two sites and that each site connects to TelMex router, correct?

If this is the case, the best way for you to go is not to use BGP with Loopback to Loopback setup for loadbalancing, but to use link aggregation method on the side with 2x2Mb. The easiest one is MLPPP (multilink PPP). You need TelMex to configure MLPPP on their router and you will need to configure on yours.

This will create a logical Multilink interface with IP assigned to it. You can then run a tunnel (GRE) between your two sites and extend your OSPF process over this tunnel.

If TelMex are provisioning a Frame Relay PVCs for you, you can MLFR (multilink Frame Relay) to achieve the same results as MLPPP.

HTH.

David

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vijayasankar Fri, 02/02/2007 - 21:05

Hi Alex,

Kindly let us know what is the problem you are facing in the current setup.

If you could provide us full scenario details, it will be really helpful for us to analyse the same.

How the 2x2 mbps links at brasil is terminated?

Are they terminated on the same router or in a different routers??

-VJ

luiz.alexandre.... Sun, 02/04/2007 - 14:24

Hi VJ,

At our side both 2Mbps links are at same router, and SP is saying that in order to share load at them need to use BGP. I don't like this idea because am affraid of having this traffic mixed to my OSPF.

I'm placing a very simple draw of this scenario.

Rds,

Alex

Correct Answer
dknov Sun, 02/04/2007 - 23:11

Hi Alex,

I would assume that this is NOT point-to-point link between your two sites and that each site connects to TelMex router, correct?

If this is the case, the best way for you to go is not to use BGP with Loopback to Loopback setup for loadbalancing, but to use link aggregation method on the side with 2x2Mb. The easiest one is MLPPP (multilink PPP). You need TelMex to configure MLPPP on their router and you will need to configure on yours.

This will create a logical Multilink interface with IP assigned to it. You can then run a tunnel (GRE) between your two sites and extend your OSPF process over this tunnel.

If TelMex are provisioning a Frame Relay PVCs for you, you can MLFR (multilink Frame Relay) to achieve the same results as MLPPP.

HTH.

David

luiz.alexandre.... Mon, 02/05/2007 - 02:52

Hi David,

It's really a very good idea, don't know why forgot this. And enjoying you help, do you have some sample of working configuration for this. I believe the fastest way to make it work will be sending a ready configuration to Telmex.

Tks,

Alex

luiz.alexandre.... Mon, 02/12/2007 - 17:01

Hi David,

I Agree 100% on you, but only concern is about 02x 02Mbps links. When one od them is dropped, how long will it take to assume that available bandwidth is lower and set transmisson window down at 04 mbps side? Do you know how can I prevent this or at least make it faster?

Rds,

Alex

dknov Mon, 02/12/2007 - 17:53

Alex,

Well, this is a perfect example you would see in traffic-shaping documents :-)

Multilink is negotiated during PPP LCP between your router and TelMex PE. If one of the links in the bundle fails I do not see any automatic way you could control lowering traffic rate from 4Mb side, except to manually apply traffic-shaping/traffic-policing on GRE tunnel between the sites. Unfortunately, I do not believe there is any automatic measure that can be taken :-(

Here is the link how to apply it on GREs:

http://www.cisco.com/en/US/tech/tk543/tk545/technologies_tech_note09186a008017405e.shtml

HTH,

David

luiz.alexandre.... Mon, 02/12/2007 - 18:08

David,

And what about TCP? Do you thing even taking some time,it would set down the transmission window or it will remain dropping packets?And I keep still more concerned because that would cause retransmission.

Do you thisnk this is going to happen?

Rds,

Alex

rmujeeb81 Wed, 02/14/2007 - 23:18

Hello,

We just tested MLPPP over FR for a similar scenario and I want to share a point here is that the convergence takes few seconds if 1 link goes down. I want to ask about how it will work if both links are of different bandwidth , let suppose 1 link is of 64kbps and 2nd is of 512kbps so what will happen if bandwidth utilization exceeds 64kbps.

Regards,

Mujeeb

dknov Thu, 02/15/2007 - 15:30

Alex,

TCP will follow its normal operation. If you try to push 4Mb of data through 2Mb of pipe, naturally drops will eventually occur. TCP will be "smart" enough to lower window size and slower the transmission rate.

So basically TCP will adopt, however other protocols, such as UDP will not.

David

luiz.alexandre.... Fri, 02/16/2007 - 16:56

Hi David,

But my concern is about the client server applications such as SAP or even IP Videoconferences that from my point of view do not stand this issue. Dou you if there some way to calculate this time until the TCP window to be lowed?

Rds,

Alex

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