Find client IP connected to VLAN from Cisco Catalyst 3600 by SNMP

Question

I would like to get using of course SNMP, list of client IPs connected to VLAN in Cisco Catalyst 3600.

So far, I have pseudo-algorithm made by me which obtains those IP addresses, but I am not sure if this is done in right way :

1) Receive all IP addresses from Catalyst (oid 1.3.6.1.2.1.4.20.1.2) I get something like :

IP-MIB::ipAdEntIfIndex.10.10.2.1 = INTEGER: 152

IP-MIB::ipAdEntIfIndex.10.10.2.251 = INTEGER: 152

IP-MIB::ipAdEntIfIndex.10.10.3.251 = INTEGER: 151 and so on.

2) Get ifIndex of VLAN (oid 1.3.6.1.2.1.4.20.1.2.10.10.2.1.<IP_ADDRESS>) for particular IP address from above list :

IP-MIB::ipAdEntIfIndex.10.10.2.1 = INTEGER: 152

IP-MIB::ipAdEntIfIndex.10.10.2.251 = INTEGER: 152

IP-MIB::ipAdEntIfIndex.10.10.3.251 = INTEGER: 151

3) Get VLAN name (oid 1.3.6.1.4.1.9.9.46.1.3.1.1.4.1.<IF_INDEX>) If_index is borrowed from list above :

IP-MIB::ipAdEntNetMask.152 = No Such Instance currently exists at this OID

IP-MIB::ipAdEntNetMask.151 = No Such Instance currently exists at this OID

In the third step I have this problem, that instance can not be found in OID. It is weird, because for about forty IP addresses i can find about their 10 VLAN names to which they are connected. Or perhaps I am doing this wrong ?

Answer 1

I managed also obtain new algorithm to find those IPs connected to VLAN :

1) Obtain index value which uniquely identifies the interface to which this entry is applicable (oid : 1.3.6.1.2.1.4.20.1.2)

Example output :

IP-MIB::ipAdEntIfIndex.10.10.2.1 = INTEGER: 152
IP-MIB::ipAdEntIfIndex.10.10.2.251 = INTEGER: 152
IP-MIB::ipAdEntIfIndex.10.10.3.250 = INTEGER: 151
IP-MIB::ipAdEntIfIndex.10.10.3.251 = INTEGER: 151
IP-MIB::ipAdEntIfIndex.10.100.0.1 = INTEGER: 312
IP-MIB::ipAdEntIfIndex.10.100.0.251 = INTEGER: 312

and so on...

2) Get name of interfaces on Catalyst 3600 using above index (oid : 1.3.6.1.2.1.31.1.1.1.1.<INTERFACE_INDEX>)

Example output (for index = 152) :

IF-MIB::ifName.152 = STRING: Vl206

3) Extract IP address from step 1) for particular Interface index. For example for index 152 it will be IP addresses like :

10.10.2.1

10.10.2.251

connected to VLAN called Vl206

I hope that I did it well.