[j-nsp] load balancing between juniper routers for unequal cost path

[Andy Lamontagne]

Hi Hamid,

To control (or engineer) where you want traffic to go, you simply introduce
MPLS LSPs.  The beauty of MPLS is its *Traffic
Engineering*characteristics.  You can decide EXACTLY where you want
your traffic to go.
So, if you have 2 unequal paths, and you wish to load-balance between the 2,
you simply need make the "more expensive" path appear to be "less
expensive", by creating those Label Switched Paths (LSPs).

For example.

Let us say that you have 3 routers connected in series (Router A, B and C)
and that all links are GigabitEthernet.  Router A also has a direct path to
Router C (also GigabitEthernet) - see ascii diagram below:

Router A ------ Router B ------ Router C
   |------------------------------------------|

Now, with default settings, the "shortest" path from Router A is the direct
link to Router C.  The other link from Router A through Router B, then
Router C is also a valid path, but at a higher "cost".  We have 2 unequal
paths from Router A to Router C.

You are looking to load balance between these 2 paths.

To do so, you create an RSVP Signaled LSP from Router A to Router C (RSVP so
that you can "force" the path of the LSP to use Router B as opposed to going
directly from Router A to Router C)

When you create this new LSP, it appears in the routing table inet.3.  To be
able to use this new "route" with OSPF, you must export it to the
inet.0routing table.  Once the LSP is in
inet.0, there will be 2 different, equal paths from Router A to Router C.
At this point, you follow Chris' config to do the load balancing and your
good to go.

You're on the right track when you the talk about using 2x GRE tunnels, but
do this with MPLS instead.

I can still send you the config examples if you need it :-)

-Andy


On Nov 8, 2007 11:39 AM, Hamid Ahmed <hamidahmed77 at yahoo.com> wrote:

> Hi Andy,
> Thanks for your reply.
> 1) Can u send me a sample configuration of what u are saying with a brief
> explanation of your scenario?
> 2) You are giving the explanation for equal cost paths. However in my case
> there are two unequal cost paths. So my question still how can u do that in
> using unequal cost paths ?
> 3) Please explain when u say the following:
> *"**What you will need to do is create 2 different RSVP Signaled LSPs
> towards the router which you want to "add more traffic", then you need to
> export these 2 LSPs in OSPF (not turn OSPF off!) so that the routing
> protocol  can see and use these 2 new paths. In the end, you will have 2
> equals paths going in 1 direction, and a
> single path in the other.  If you need to move more traffic, then simply
> add a  3rd, 4th, etc LSP.*"
> 4) The above discussion is for when we are doing work within MPLS. Now in
> my case my intended traffic (Voice) does not use MPLS(however MPLS is
> enabled but for some other traffic like sigtran and O/M). OSPF is there as
> IGP and i need to load balance my intended traffic using the unequal cost
> path. I have an idea taht i create 2 x static GRE tunnels from one end to
> the other. My question can GRE tunnel override OSPF as that would be purely
> static routing and whatever goes with the tunnels would be just IP-payload.
>
> regards,
> HA.
>
>
> *Andy Lamontagne <alamontagne at gmail.com>* wrote:
>
> Hi Hamid,
>
> To expand on Chris's explanation, ECMP is Equal Cost Multi-Path, which
> allows for the use of 2 (or more) equal cost path at the same time; Load
> balancing the traffic between the different paths. As Chris also mentioned,
> this load balancing is done per flow and not per packet, so you don't get
> any reordering of packets.
>
> What you will need to do is create 2 different RSVP Signaled LSPs towards
> the router which you want to "add more traffic", then you need to export
> these 2 LSPs in OSPF (not turn OSPF off!) so that the routing protocol can
> see and use these 2 new paths.
>
> In the end, you will have 2 equals paths going in 1 direction, and a
> single path in the other.  If you need to move more traffic, then simply add
> a 3rd, 4th, etc LSP.
>
> Please let me know if you need further explanation/configuration samples.
>
> -Andy
>
> On 11/8/07, Hamid Ahmed <hamidahmed77 at yahoo.com> wrote:
> >
> > Hi,
> >   Its LAyer 3 load balancing. The traffic intended for load-balancing
> > does is on pure IP with OSPF running and having unequal cost paths
> >
> >   regards,
> >   Salman.
> >
> > GAY Samuel <samuel.gay at c-s.fr> wrote:
> >   Hi,
> >
> > Which kind of load balancing do you want to do ? layer 3 ? layer 4 ?
> > Are you on a MPLS network ?
> >
> > Regards,
> > Samuel
> >
> >
> > Hamid Ahmed a écrit :
> > > Hi Everyone,
> > >
> > > CAn anyone suggest me how to load balancing between juniper routers
> > for unequal cost paths.
> > >
> > > BR//
> > > HA
> > >
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