[j-nsp] load balancing 'per flow'

[Nick Kraal]

Bosco,

If I am not mistaken you can either load-balance on multiple links on a 
per-flow or per-packet algorithm. Per-packet is as the name describes, a 
crude distribution of packets on round-robin on the links.

For per-flow packets are load-balanced on a flow basis. The 'four-tet' 
communications is maintained on one link; source address, destination 
address, source port and destination port (a flow). Other flows can/will 
be established on the other links.

Both algorithms have their advantages. Packet renumbering issues is one 
on the per-packet technique. While link saturation is an issue on 
per-flow especially when there are multiple low-bandwidth links; for 
example one flow possibly may take up the entire E1 link. There maybe 
others, but these are the common ones.

By default per-flow is used on Juniper boxes. However a policy statement 
can be introduced to configure for per-packet. In this case below is a 
policy-statement is used to influence one BGP session (with multiple E1 
links) for per-packet load-balancing, while the rest will be on a 
per-flow configuration.

policy-statement load-balancing {
         from neighbor xxx.yyy.zzz.aaa;
         then {
             load-balance per-packet;
         }
     }

autonomous-system XXXX;
     forwarding-table {
         export load-balancing;


Not really an authority on this, but I hope this is some start and look 
forward to comments from others.

Best regards,

-nick/




Bosco Sachanandani wrote:
> Hello all,
> 
> I understand that Internet Processor II only supports load balancing per flow and not per packet (as CEF does).
> 
> Can someone throw some more light on what exactly does 'per flow' mean ? The reason I am asking this is:
> 
> 1) Is it per VRF ? For eg all PE to PE traffic for VRF A will go via link 1 and all PE to PE traffic for VRF B will go via link 2?
> 
> 2) Or is it that 'flows' between various IP addresses WITHIN each VRF will go via alternate links ? For eg. Prefix 10.0.0.0/8 which is within VRF A will go via Link 1 and Prefix 20.0.0.0/8 which is also within VRF A will go via Link 2 ?
> 
> Additionally,
> For any sort of load balancing between the 2 PE to PE links, do I need to explicitly add a policy  or will it happen anyway if the IGP recognises it as equal cost links ? We are using LDP between these routers.
> 
> Any help would be great. I am running version 5.5R3.1 between 3 M20 routers.
> 
> Thanks
> 
> 
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