IP multinetting over VSX

IP multinetting is the assignment of more than one IP interface to a single VLAN that is used to enable a router to provide default gateway service to different address ranges associated with a single VLAN.

When using IP multinetting in an environment with VSX enabled, you must configure multiple active gateway IP addresses per SVI so that you can reach multiple networks on the same VLAN. Make sure that you configure an IP address for either the primary or secondary VSX switch on the SVI with the same subnet.

The maximum number of supported active gateways per switch is 4,000. Since a maximum of 31 secondary IPv4 addresses can be configured on an SVI, 32 IPv4 active gateways (along with the primary IPv4 address) can be configured per SVI with IP multinetting support. This support is also the same for IPv6 addresses.

IMPORTANT:

Disable IP ICMP redirect when IP multinetting is enabled.

Multiple active gateways IP addresses can be programmed on the same active gateway kernel interface, as shown in the following example:

interface vlan3
ip address 10.0.0.1/24
ip address 20.0.0.1/24 secondary
active-gateway ip mac 00:00:00:00:00:01
active-gateway ip 10.0.0.3
active-gateway ip 20.0.0.3

003000000000001@vlan3: <NO-CARRIER,BROADCAST,UP,M-DOWN> mtu 1500 qdisc noqueue 
state LOWERLAYERDOWN group default qlen 1000      
link/ether 00:00:00:00:00:01 brd ff:ff:ff:ff:ff:ff      
inet 10.0.0.3/32 scope global 003000000000001      
valid_lft forever preferred_lft forever      
inet 20.0.0.3/32 scope global 003000000000001     
valid_lft forever preferred_lft forever

Active gateway VMAC and VIPs can be configured separately:

interface vlan3
ip address 10.0.0.1/24
ip address 20.0.0.1/24 secondary
active-gateway ip mac 00:00:00:00:00:01
active-gateway ip 10.0.0.3
active-gateway ip 20.0.0.3