What interface does the monitoring flow through?

Hi,

If the monitor is using the mgmt gateway, your traffic will fail even if the monitor state is up. You must create a route to TMOS reach the node via traffic interface/vlan. (e.g. Create route in menu: Network > Routes) If necessary, you can create a default route (0.0.0.0/0) to the traffic gateway and by default, it will have lower metric than default route management, so the traffic will use it out instead of default mgmt. Considers that the Big-IP uses the SelfIP to monitor and FloatIP to flow the traffic (if you SNAT). If you don't have a FloatIP, everything must flow from the SelfIP.

You can test the route from the shell: e.g.

[root@bigiplab:Active:Standalone] config  route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
127.1.1.0       0.0.0.0         255.255.255.0   U     0      0        0 tmm
127.2.0.0       0.0.0.0         255.255.255.0   U     0      0        0 mgmt.1
172.20.16.0     0.0.0.0         255.255.252.0   U     0      0        0 mgmt
10.10.10.0   0.0.0.0         255.255.255.0   U     0      0        0 internal_vlan
127.7.0.0       127.1.1.253     255.255.0.0     UG    0      0        0 tmm
127.20.0.0      0.0.0.0         255.255.0.0     U     0      0        0 tmm_bp
0.0.0.0         10.10.10.1.1   0.0.0.0         UG    0      0        0 internal_vlan
0.0.0.0         172.20.16.110   0.0.0.0         UG    9      0        0 mgmt
[root@bigiplab:Active:Standalone] config  ip route get 20.10.10.1
20.10.10.1 via 10.10.10.1 dev internal_vlan  src 10.10.10.10
    cache  mtu 1500 advmss 1460 hoplimit 64

Regards.