Problem: 'I see MAC addresses - why don't I see IP addresses
The switch port mapper gathers MAC Addresses from the
switch. If you only see MAC addresses (and few or no IPv4
addresses), please understand that most switches are
layer 2 and
generally do not track/record/monitor IP addresses of connected devices unless
switch is a layer 3 or core switch like a Cisco 6509 or a Nexus. In order to get the IP addresses, we
gather ARP tables which we use to match MAC addresses to IP addresses,
There is no
magic IPv4 network protocol to ask for an IP given a MAC. The application collects ARP tables (MAC/IP
associations) from a variety of sources:
1. Your computer
- your local ARP table and through Ping Sweep - use Ping Sweep on
the parts of your local subnet that you know are populated. More on
Ping Sweep in 4 below. Make sure Query Local ARP Table
2. The switch(es) you are communicating with. If the switch is layer 2
only, the ARP table will be pretty small or completely empty. If it's layer 3,
the ARP table may be larger depending on the size of the
network handled by the switch. Make sure Query Switch
ARP Table is checked.
3. Two optional external SNMP enabled devices. If you are not using
Router/Server 1 or 2, please find an SNMP enabled router
(or nearby layer 3 switch) to query that has
visibility into the subnets and VLANs handled by the switch. Highly
important to use one or more of these devices. Remember,
they need visibility into the same subnets as the switch
4. Ping Sweep. Set Ping Sweep to
operate over the range of IPs that are actually in
use (especially important to only define the exact range on a
10.x.x.x network - do not waste time pinging known empty
IP address ranges) does two things: 1) it prepopulates any other
switches or routers with mac/IP ARP table combinations and 2)
responding IPs are probed with NetBIOS to access the mac address
given the IP - Windows and Apple Mac machines will often
respond to NetBIOS queries. Enable Ping Sweep must be
checked AND a Ping Sweep Range must be predefined.
5. Static ARP table imported through Database Maintenance. This is
useful when you have a network with many static IP devices like
networked printers, routers and switches - use Import
ARP Table. You can also enter MAC/IP addresses one at a
time manually with Add ARP Table Entry.
We recommend Router/Server 1 and 2 be a
router or a server on the network segment the switch is serving.
Those ARP tables are combined into a single ARP table for lookups (Database
Maintenance/Combined ARP Table). ARP tables are used because there is no
reliable protocol to get an IPv4 address given a MAC address.
Note that the combined ARP table is cleared on exit, this is controllable
in Global Settings.
hostnames come from a query to DNS through your
operating system. No IPs - no hostnames.