[j-nsp] Junos Load Balancing Behavior

[Doug Hanks]

It's working just the like documentation says.  It's per-prefix
load-balancing.

If you want per-flow you need to modify the FIB via an export policy.

set policy-options policy-statement fib-per-flow then load-balance
per-packet 
set routing-options forwarding-table export fib-per-flow
Commit

Check your FIB again after that change.


Thank you,

-- 
Doug Hanks - JNCIE-ENT #213,  JNCIE-SP #875
Sr. Systems Engineer
Juniper Networks


On 2/2/12 9:01 AM, "Devin Kennedy" <devinkennedy415 at hotmail.com> wrote:

>Hello:
>
> 
>
>I'm looking for some insight on the load balancing behavior that Junos
>uses
>by default.  We are certifying our Junos platform CE routers (SRX, MX10,
>M7i) and not seeing what we expected given the documentation we have.
>
> 
>
>According to the Juniper docs and the old JNCIP study guide, OSPF will
>automatically load balance if there are two equal cost routes.  And indeed
>in the routing table we have default route advertised via OSPF to a CE
>router which shows two next hops (one to each of two PE's).
>
> 
>
>juniper at SRX240-5> show route 0/0 exact
>
> 
>
>inet.0: 23 destinations, 23 routes (23 active, 0 holddown, 0 hidden)
>
>+ = Active Route, - = Last Active, * = Both
>
> 
>
>0.0.0.0/0          *[OSPF/150] 20:45:21, metric 112, tag 13979
>
>                      to 10.7.122.1 via ge-0/0/6.0
>
>                    > to 10.7.122.2 via ge-0/0/6.0
>
> 
>
>However in the forwarding table there is only one next-hop shown and when
>testing traffic flows we don't see any load balancing by default.
>
> 
>
>juniper at SRX240-5> show route forwarding-table destination 0/0
>
>Routing table: default.inet
>
>Internet:
>
>Destination        Type RtRef Next hop           Type Index NhRef Netif
>
>default            user     0                    ulst 262142     2
>
>                              80:71:1f:c0:3c:81  ucst   584     4
>ge-0/0/6.0
>
>default            perm     0                    rjct    36     4
>
>0.0.0.0/32         perm     0                    dscd    34     2
>
> 
>
>Routing table: __master.anon__.inet
>
>Internet:
>
>Destination        Type RtRef Next hop           Type Index NhRef Netif
>
>default            perm     0                    rjct   517     1
>
>0.0.0.0/32         perm     0                    dscd   515     1
>
> 
>
>Everything goes across the one next hop only (the one with the > in front
>of
>it).  We have to add an export policy to the routing-options
>forwarding-table stanza to get it to work.
>
> 
>
>This is from the Junos documentation for OSPF for version 10.4:
>
> 
>
>"When several equal-cost routes to a destination exist, traffic is
>distributed equally among them."
>
> 
>
>http://www.juniper.net/techpubs/en_US/junos10.4/topics/concept/ospf-routin
>g-
>overview.html
>
> 
>
>Shouldn't the load balancing work by default as the documentation would
>lead
>one to believe?  Does anyone have any insight into this?  Is the
>documentation incorrect and you actually are required to always add a
>load-balancing export policy in order to get the desired load-balancing
>behavior?
>
> 
>
> 
>
> 
>
>Best Regards,
>
> 
>
>Devin J Kennedy
>
>Juniper Engineer - AT&T Labs
>
> 
>
> 
>
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