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

[Phil Bedard]

If your best path for the majority of VPRN routes is one exit router (next-hop), all of that traffic will only take one physical link due the routes using the same VPN label.   

8.0 supports entropy labels, where the PE uses a hash based on the incoming IPv4 src/dst to create a new bottom of stack label.  ALU uses a reserved set of labels 512k-1M so when the label hits the egress PE it knows it is an entropy label.   It's meant to solve the problem you are seeing, but it requires 8.0 and chassis-mode C (all IOM-2s).  

Phil  


On Mar 8, 2010, at 7:17 PM, Scott Weeks wrote:

> 
> --- 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
> |       |
> |       |
> 7750----7750
> |\       /|
> | \     / |
> |  \   /  |
> |   \ /   |
> |    X    |
> |   / \   |
> |  /   \  |
> | /     \ |
> |/       \|
> 7750----7750====7750
>             ^
>             |
> 
> 
> 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.  :-)
> scott
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