[SNMP] ifAlias and ifDescr

I have some vlans and they're not called 0,1,2 as shown below. Why does it show my vlans with the wrong vlan ids?

# snmpwalk -v2c -c public 1.2.3.4 ifDescr
IF-MIB::ifDescr.1 = STRING: em0
IF-MIB::ifDescr.2 = STRING: em1
IF-MIB::ifDescr.3 = STRING: em2
IF-MIB::ifDescr.4 = STRING: em3
IF-MIB::ifDescr.5 = STRING: em4
IF-MIB::ifDescr.6 = STRING: em5
IF-MIB::ifDescr.7 = STRING: em6
IF-MIB::ifDescr.8 = STRING: em7
IF-MIB::ifDescr.9 = STRING: em8
IF-MIB::ifDescr.10 = STRING: em9
IF-MIB::ifDescr.11 = STRING: em10
IF-MIB::ifDescr.12 = STRING: em11
IF-MIB::ifDescr.13 = STRING: enc0
IF-MIB::ifDescr.14 = STRING: lo0
IF-MIB::ifDescr.15 = STRING: vlan0
IF-MIB::ifDescr.16 = STRING: vlan1
IF-MIB::ifDescr.17 = STRING: vlan2
IF-MIB::ifDescr.18 = STRING: ipfw0
IF-MIB::ifDescr.19 = STRING: gif0




ifAlias is not showing anything. Wouldn't it be nice if it was showing the interface description from the WebGUI? Like LAN, WAN etc.

# snmpwalk -v2c -c public 1.2.3.4 ifAlias
IF-MIB::ifAlias.1 = STRING:
IF-MIB::ifAlias.2 = STRING:
IF-MIB::ifAlias.3 = STRING:
IF-MIB::ifAlias.4 = STRING:
IF-MIB::ifAlias.5 = STRING:
IF-MIB::ifAlias.6 = STRING:
IF-MIB::ifAlias.7 = STRING:
IF-MIB::ifAlias.8 = STRING:
IF-MIB::ifAlias.9 = STRING:
IF-MIB::ifAlias.10 = STRING:
IF-MIB::ifAlias.11 = STRING:
IF-MIB::ifAlias.12 = STRING:
IF-MIB::ifAlias.13 = STRING:
IF-MIB::ifAlias.14 = STRING:
IF-MIB::ifAlias.15 = STRING:
IF-MIB::ifAlias.16 = STRING:
IF-MIB::ifAlias.17 = STRING:
IF-MIB::ifAlias.18 = STRING:
IF-MIB::ifAlias.19 = STRING: