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Posts: 39
Registered: ‎03-10-2008
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route selection in OSPF

Hi all, I got an issue with route selection in OSPF. If I have 5 intra-area routes all of equal cost, what that JUNOS does...I have ECMP enabled through a policy under routing-options..I expect it to do a load-balancing per-flow..Am I right?

Juniper Employee
Posts: 13
Registered: ‎09-23-2008
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Re: route selection in OSPF

In Junos the OSPF load balancing is per destination by default.


You can change it to per flow by using the following configuration (NOTE: per-packet == per-flow)


routing-options {      

forwarding-table {          
export load-balancing-policy;      }  }  

policy-options {      

policy-statement load-balancing-policy {          
then {              
load-balance per-packet;          }   }  }
I hope this helps 
New User
Posts: 1
Registered: ‎09-12-2008
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Re: route selection in OSPF

Traffic pattern will vary depending on the ASIC.  Internet Processor I ASIC is truely per packet while II's are per flow.


Super Contributor
Posts: 96
Registered: ‎09-26-2008

Re: route selection in OSPF

Hi Shiv,


It also depends upon the spread of the sources/destinations.  The actual hash algorithms used to decide which of the equal cost paths to use are proprietary and not published.  However, I can say that if you have a very small cluster of sources and a very small cluster of destinations, there is a possibility that the balancing will not be very... well... balanced.  With a reasonable spread of src/dst IP addresses, you'll get a fair (but never perfect) balance.