Unable to get hostname and IP address in other subnets
2 posts · Closed
Our customer has been testing Switch Port Mapper. And it seems that in one network segment, they could get information, such as hostname and IP address.
But when they tried to get the same information in other subnets, they could not get it. Can they do anything to get that information??
This is normal behaviour:
- When MAC address mapping is done in the same subnet, the software can ARP-scan the entire IP address range and map MAC addresses to their respective IP addresses.
- When MAC address mapping is done in a different subnet, the above method won't work because the ARP protocol is not routable and only works in the local subnet.
To overcome this issue, it is possible to specify the subnet router in the settings. As the router sits between two subnets, it knows client MAC addresses on both sides. So it works for both local and non-local subnets.
The router may need to be specially configured to provide this information via SNMP. There are three common OIDs (Object Identifiers) where SNMP-capable routers keep IP-to-MAC-address mapping tables:
iso.org.dod.internet.mgmt.mib-2.ip.ipNetToPhysicalTable iso.org.dod.internet.mgmt.mib-2.at.atTable.atEntry iso.org.dod.internet.mgmt.mib-2.ip.ipNetToMediaTable
The router needs to support at least one of these, have SNMP enabled, and a community string set.