[alcatel-nsp] unbalanced traffic on GigEs in a LAG

GARCIA DEL RIO Diego Diego.Garcia_Del_Rio at alcatel-lucent.com
Mon Mar 8 22:10:33 EST 2010

Hi Guys,

The load balancing really depends on whether the system can see the IP
or MAC layer of the services or not, so, if the node is taking traffic
through a SAP or a network port but traffic is pure IP-over-Ethernet
when it enters the node, then traffic will be nicely balanced and hashed
based on SRC/DST ports and IPs. If the node is acting as a pure LSR,
though, we don't normally look at the upper layers (anything beyond the
label stack) as this can cause some issues with Ethernet-over-MPLS
traffic being mistakenly identified as IPv4 or IPv6 (if a 0x4 or 0x6 is
present where the IP version field is, we would identify the packet as
IP while its in reality Ethernet).

7.0 R5 (I think) introduced the following command:

configure system lsr-load-balancing lbl-ip

which allows you to look at both IP and MPLS layers in an LSR node. This
should really be used in pure IP environments, though in some cases, it
might be applicable to mixed services (L2 MPLS VPNs and L3 MPLS VPNs).
Please check the documentation and your local Alcatel-Lucent point of
contact for more information.


Diego Garcia del Rio
701 E. Middlefield Rd
Mountain View CA 94043
Mobile: +1 (415) 439-9420
OnNet: 2852-2726

-----Original Message-----
From: alcatel-nsp-bounces at puck.nether.net
[mailto:alcatel-nsp-bounces at puck.nether.net] On Behalf Of Scott Weeks
Sent: Monday, 8 March 2010 4:18 PM
To: alcatel-nsp at puck.nether.net
Subject: Re: [alcatel-nsp] unbalanced traffic on GigEs in a LAG

--- philxor at gmail.com wrote:
From: Phil Bedard <philxor at gmail.com>

I guess it's hard to know exactly which services are flowing across the 
link but if it's only acting as an LSR then it should be hashing based 
on the MPLS stack (Up to 5 labels), ingress port, and system ID.   Are 
there any potential really high BW services across the LAG?  With the 
IOM3/IMM you can have it hash on both the labels and the IPv4 header, 
but not on the IOM2.  

If there are services originating on the box there are all kinds of 
rules on how things are hashed on egress, but LSR it's pretty simple.  

We carry our internet traffic in a VPRN.  This is 99+% of all traffic.  
I'm guess I'm going to have to go with just 2 cases of bad load 
balancing.  The network goes something like this:

br1     br2
 |       |
 |       |
|\       /|
| \     / |
|  \   /  |
|   \ /   |
|    X    |
|   / \   |
|  /   \  |
| /     \ |
|/       \|

No links are full.  The 'middle' is 10G and the 'edges' are multi-GigE.
br1 has about twice the bandwidth as br2, so perhaps the label from br2
is hashed over one of the 2 GigEs (above the arrow) and the label of br1
is over the other  and it's just a case of bad load balancing.  More
that 10 to 1, though, seems excessive.

Thank you everyone on and off-list for your help.  :-)
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