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@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@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
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