Not the most elegant way, but I have usually fallen back to a MIB walk of the device. It will show you what is where. Something like this will appear:
1.3.6.1.2.1.2.2.1.1.2 IF-MIB.ifIndex.2 Integer32 2
1.3.6.1.2.1.2.2.1.1.3 IF-MIB.ifIndex.3 Integer32 3
1.3.6.1.2.1.2.2.1.1.4 IF-MIB.ifIndex.4 Integer32 4
1.3.6.1.2.1.2.2.1.1.5 IF-MIB.ifIndex.5 Integer32 5
1.3.6.1.2.1.2.2.1.1.6 IF-MIB.ifIndex.6 Integer32 6
1.3.6.1.2.1.2.2.1.1.7 IF-MIB.ifIndex.7 Integer32 7
1.3.6.1.2.1.2.2.1.1.8 IF-MIB.ifIndex.8 Integer32 8
1.3.6.1.2.1.2.2.1.1.9 IF-MIB.ifIndex.9 Integer32 9
1.3.6.1.2.1.2.2.1.2.2 IF-MIB.ifDescr.2 OCTET-STRING Adaptive Security Appliance outside interface
1.3.6.1.2.1.2.2.1.2.3 IF-MIB.ifDescr.3 OCTET-STRING Adaptive Security Appliance inside interface
1.3.6.1.2.1.2.2.1.2.4 IF-MIB.ifDescr.4 OCTET-STRING Adaptive Security Appliance DMZ interface
1.3.6.1.2.1.2.2.1.2.5 IF-MIB.ifDescr.5 OCTET-STRING Adaptive Security Appliance Guest interface
1.3.6.1.2.1.2.2.1.2.6 IF-MIB.ifDescr.6 OCTET-STRING Adaptive Security Appliance Management0/0 interface
1.3.6.1.2.1.2.2.1.2.7 IF-MIB.ifDescr.7 OCTET-STRING Adaptive Security Appliance Virtual254 interface
1.3.6.1.2.1.2.2.1.2.8 IF-MIB.ifDescr.8 OCTET-STRING Adaptive Security Appliance state interface
1.3.6.1.2.1.2.2.1.2.9 IF-MIB.ifDescr.9 OCTET-STRING Adaptive Security Appliance failover interface
So, you can see that outside is ifIndex 2 and inside is 3.
It also shows up again further down:
1.3.6.1.2.1.4.20.1.2.10.3.1.254 IP-MIB.ipAdEntIfIndex.10.3.1.254 Integer32 3
Where you see the IP address along with the ifIndex number.
Hope that helps,
Bill
