The OOB "mgmt" interface can be configured with a default gateway specifically for routing "mgmt" traffic only.
Here's my config:
I have a "mgmt" ip address of 10.10.10.1 and a default gateway of 10.10.10.254 that will apply ONLY to "mgmt" interface traffic.
(MM1) [mynode] #show ip interface brief
Interface IP Address / IP Netmask Admin Protocol VRRP-IP
vlan 1 192.168.1.240 / 255.255.255.0 up up
loopback unassigned / unassigned up up
mgmt 10.10.10.1 / 255.255.255.0 up up
(MM1) [mynode] #show ip route
Codes: C - connected, O - OSPF, R - RIP, S - static, B - Bgw peer uplink
M - mgmt, U - route usable, * - candidate default, V - RAPNG VPN/Branch
I - Ike-overlay, N - not redistributed
Gateway of last resort is Imported from DHCP to network 0.0.0.0 at cost 10
Gateway of last resort is Imported from CELL to network 0.0.0.0 at cost 10
Gateway of last resort is Imported from PPPOE to network 0.0.0.0 at cost 10
Gateway of last resort is 192.168.1.1 to network 0.0.0.0 at cost 1
S* 0.0.0.0/0 [0/1] via 192.168.1.1*
C 192.168.1.0/24 is directly connected, VLAN1
C 192.168.1.241/32 is an ipsec map default-local-master-ipsecmap
M 10.10.10.0/24 is directly connected to mgmt interface
Management Gateway of last resort is 10.10.10.254 to network 0.0.0.0
M* 0.0.0.0/0 via 10.10.10.254*
To do this set the ip address on the "mgmt" interface then execute the command:
(MM1) [mynode] #ip default-gateway mgmt x.x.x.x
-enjoy