Any idea why the "file exists" error happens on this ip route command to load balance two uplinks?
I tried doing these
ip route add default via 205.237.100.209
ip route add default via 205.237.100.209 dev em2
but neither had any effect.

+ /sbin/ip route add default scope global nexthop via 205.237.100.209 dev em2 weight 1 nexthop via 216.36.102.185 dev em4 weight 1
RTNETLINK answers: File exists

# ip route list
216.36.102.248 dev em4 scope link src 216.36.102.189
205.237.100.0 dev em2 scope link src 205.237.100.217
216.36.102.184/29 dev em4 proto kernel scope link src 216.36.102.189
192.168.100.0/24 dev em1 proto kernel scope link src 192.168.100.217
205.237.100.0/24 dev em2 proto kernel scope link src 205.237.100.217
169.254.0.0/16 dev em1 scope link metric 1002
169.254.0.0/16 dev em2 scope link metric 1003
169.254.0.0/16 dev em4 scope link metric 1005
192.168.0.0/16 via 192.168.100.210 dev em1
default via 216.36.102.185 dev em4


# ip route list table T1
192.168.100.0 dev em1 scope link
216.36.102.248 dev em4 scope link
205.237.100.0 dev em2 scope link src 205.237.100.217
127.0.0.0/8 dev lo scope link
default via 205.237.100.209 dev em2

# ip route list table T2
192.168.100.0 dev em1 scope link
216.36.102.248 dev em4 scope link src 216.36.102.189
205.237.100.0 dev em2 scope link
127.0.0.0/8 dev lo scope link
default via 216.36.102.185 dev em4

Figured it out...Centos/RHEL's auto network startup adds a default.
So in this script, I had to get rid of any previous defaults:

ip route del default via 205.237.100.209 dev em2
ip route dell default via 216.36.102.185 dev em4

And then executing the load-balancing default works...