One interface with two ip addresses

[Nakedape]

I'm trying to understand why and how my FreeNas box has two ip addresses on the igb0 interface. I can reach the FreeNas GUI from both the x.x.x.12 and the x.x.x.18 IP's. Can someone point me in the right direction?

Code:

root@freenas[~]# ifconfig
igb0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
        description: LAN Connection
        options=6403bb<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,
                     VLAN_HWCSUM,TSO4,TSO6,VLAN_HWTSO,RXCSUM_IPV6,TXCSUM_IPV6>
        ether 0c:c4:7a:b7:22:62
        hwaddr 0c:c4:7a:b7:22:62
        inet 192.168.30.12 netmask 0xffffff00 broadcast 192.168.30.255
        inet 192.168.30.18 netmask 0xffffff00 broadcast 192.168.30.255
        nd6 options=9<PERFORMNUD,IFDISABLED>
        media: Ethernet autoselect (1000baseT <full-duplex>)
        status: active
<snip>

Code:

root@freenas[~]# netstat -4 -r -n
Routing tables

Internet:
Destination        Gateway            Flags     Netif Expire
default            192.168.30.1       UGS        igb0
127.0.0.1          link#3             UH          lo0
192.168.30.0/24    link#1             U          igb0
192.168.30.12      link#1             UHS         lo0
192.168.30.18      link#1             UHS         lo0

 

[dexll]

Bumping this. I don't understand this either.

Booted into the console this morning and saw the web gui had two different IPs. Both work. Why?