[j-nsp] Junos Load Balancing Behavior

[Devin Kennedy]

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-routing-
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