[c-nsp] load sharing Vs load balancing - MPLS VPN Topology consideration

Tue Nov 28 06:38:46 EST 2006

Oli .

Thanks for the reply . Really usefull as usually . There is just one last 
thing i don't understand . I have made some testing in my lab here . As 
you can see below my PE router is now able to install 2 routes to the same 
destination in his Vrf routing table .That is fine .

R2#sh ip bgp v v test 192.168.10.0
BGP routing table entry for 2:551012:192.168.10.0/24, version 68
Paths: (2 available, best #2, table test)
Multipath: iBGP
Flag: 0x820
  Advertised to update-groups:
     2
  65000, imported path from 2:551011:192.168.10.0/24
    10.152.65.3 (metric 2297856) from 10.152.65.3 (10.152.65.3)
      Origin IGP, metric 0, localpref 100, valid, internal, multipath
      Extended Community: RT:551:0
      mpls labels in/out nolabel/21
  65000, imported path from 2:551013:192.168.10.0/24
    10.152.65.1 (metric 2297856) from 10.152.65.1 (10.152.65.1)
      Origin IGP, metric 0, localpref 100, valid, internal, multipath, 
best
      Extended Community: RT:551:0
      mpls labels in/out nolabel/21
R2#

R2#sh ip route vrf test 192.168.10.0
Routing entry for 192.168.10.0/24
  Known via "bgp 10", distance 200, metric 0
  Tag 65000, type internal
  Last update from 10.152.65.3 00:00:06 ago
  Routing Descriptor Blocks:
    10.152.65.3 (Default-IP-Routing-Table), from 10.152.65.3, 00:00:06 ago
      Route metric is 0, traffic share count is 1
      AS Hops 1
      Route tag 65000
  * 10.152.65.1 (Default-IP-Routing-Table), from 10.152.65.1, 00:03:23 ago
      Route metric is 0, traffic share count is 1
      AS Hops 1
      Route tag 65000

Now Cisco clearly state the following :
"Even if the criteria are met and multiple paths are considered 
multipaths, a BGP speaking router will still designate one of the 
multipaths as the best path and advertise this best path to its 
neighbors."

Well this is exactly what is happening here . As you can see in my output 
the route to 192.168.10.0/24 is prefer via Next hop 10.152.65.1. 
So the question is if only ONE of the path is still designated as prefer , 
how is the router going to load-share between the two ? 

Best regards .
David

Internet
oboehmer at cisco.com

27/11/2006 16:59

To
David PONSDESSERRE
cc
cisco-nsp, cisco-nsp-bounces, sthaug
Subject
RE: load sharing Vs load balancing

david.ponsdesserre at uk.bnpparibas.com <> wrote on Monday, November 27,
2006 5:36 PM:

> Hello again people .
> 
> I need to come up with a load balancing solution for one of our
> customer . I have a question , may be it is a bit dumb but .... What
> is the actual difference between load balancing and load sharing ?

Well, both terms usually mean the same thing: Some technology to split
the load over multiple links.

> We will be using mainly Cisco Kit with Ebgp between our Pes
> and customers Ces  ( It is an Mpls connection )
> If you have any best practices on load balancing
> implementation other Ebgp please forward !!!

You might want to elaborate given the topology you have in mind, but in
MPLS networks, you ususally need some form of BGP multipath to split the
load. There are some standard scenarious:

                  PE2 -- CE2 \
CE1 --- PE1                   host
                  PE3 -- CE3 /

you need iBGP multipath to have the traffic from CE1 to use both PE2-CE2
and PE3-CE3 links.

If you have

     PE2 === CE2

you need eBGP multipath on the PE2 to use both links from PE2 to CE2
(assuming you use BGP as PE-CE)

There is another method specific to MPLS-VPN: eiBGP multipath:

                  CE4
                   |
                   |
                   |
                  PE2 -- CE2 \
CE1 --- PE1                   host
                  PE3 -- CE3 /

You need eiBGP multipath if you also want the traffic from CE4 to the
host behind CE2/CE3 to use both the direct eBGP link via CE2, as well as
the other link via PE3 to CE3.

Hope it helps..

                 oli

This message and any attachments (the "message") is 
intended solely for the addressees and is confidential. 
If you receive this message in error, please delete it and
immediately notify the sender. Any use not in accord with
its purpose, any dissemination or disclosure, either whole
or partial, is prohibited except formal approval. The internet
can not guarantee the integrity of this message.
BNP PARIBAS (and its subsidiaries) shall (will) not
therefore be liable for the message if modified. 

**********************************************************************************************

BNP Paribas Private Bank London Branch is authorised
by CECEI & AMF and is regulated by the Financial Services
Authority for the conduct of its investment business in
the United Kingdom.

BNP Paribas Securities Services London Branch is authorised 
by CECEI & AMF and is regulated by the Financial Services 
Authority for the conduct of its investment business in 
the United Kingdom.

BNP Paribas Fund Services UK Limited is authorised and 
regulated by the Financial Services Authority