Problem: 'I see MAC addresses - why don't I see IP addresses or hostnames?'
The switch port mapper reports MAC Addresses assigned
to ports from the
switch bridge tables for both layer 2 or 3 switches. If you only see MAC addresses (and few or no IPv4
addresses) your switch is most likely
layer 2 which means
it does not track/record/monitor IP addresses - it
routes packets to switch ports based on the destination
MAC addresses only. That means a layer 2 switch has a small
ARP table. Layer 3 switches perform routing functions
and are often called a core switch (examples: Cisco 6509 or a Nexus
or an HPE stack). Layer 3 switches usually have a large
ARP table because they monitor the IP addresses of
attached devices for correct VLAN routing.
For a
layer 2 or 3 switch 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 address given a MAC
address. 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
is checked.
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 large depending on the size of the
network handled by the switch. For layer 2 or 3 make sure Query Switch
ARP Table is checked.
3. Two optional external SNMP enabled devices -
Router/Server 1 and 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
subject switch. Highly
important to use one or more of these devices. Remember,
they need visibility into the same subnets as the switch
is processing. Firewalls typically are not a good choice
because SNMP is often disabled.
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.
No hostnames?
hostnames come from a query to DNS through your
operating system. No IPs - no hostnames.
Problem: I get error message "Switch Communications Failure - First SNMP Query. Switch IP ..." (a timeout) when trying to map my switch. It's strange because the app maps my other switches just fine!
Background: This error means that we tried to
retrieve the device RFC1213-MIB::sysObjectID to find out
what kind of switch it is and nothing came back - this
is our very first SNMP query. If the switch or any SNMP
device supports SNMP, it MUST respond with this value -
it is a mandatory item.
Note: if it maps your
other switches, especially the same model switch, then
the problem is settings - most likely in the switch but
also possibly in the Switch Port Mapper.
Solution: The Switch Port Mapper presents you with a
dialog box with things to check. Here is the list with
some expanded explanations in italics. [SW] below means
switch and [SPM] means this software. Same Switch Model
Only: It can also be a firmware revision issue - check
the firmware rev of the switch that does map and see if
it is the same as the switch that does not map.
Check your settings in the switch [SW] and this program
[SPM]:
1. [SW][SPM] Is switch IP address correct?
(Verify the switch IP address and make sure the IP
address in the left control panel is the same - also try
pinging the switch from a command prompt to ensure you
can reach the switch from your computer)
2. [SW][SPM]
Does the switch support the SNMP version you have chosen
in Settings? (Use your web interface or CLI to verify
that the switch has SNMP enabled and the version(s) you
want to use are active. Confirm this in Left Control
Panel/Switch Settings/Settings button/SNMP Version.)
3. [SW] Is SNMP enabled on the switch? (Use your web
interface or CLI to verify that the switch has SNMP
enabled)
4. [SW][SPM] Do you have the correct
Community Name (SNMPv1/v2c) or Credentials (SNMPv3)?
(Use your web interface or CLI to verify switch
community name, then go into SPM Settings for the switch
and verify)
5. [SW] Is this computer on the switch\'s
SNMP IP access permission list? (sometimes called an
access control list ACL - if your switch uses this and
it's enabled, you will need to be on it in order for us
to talk to the switch)
6. [SW] Does your switch have
levels of user permissions? If so, do you have
sufficient permissions? (some switch have as many as 15
levels of user permissions. If your switch uses
permissions and they are enabled, be sure that you have
permission to read all switch OIDs using SNMP)
SNMPv3: If you are trying to use SNMPv3 and it is not
working, then revert back to SNMPv2c or even SNMPv1 to
make sure you can actually talk to the switch. You may
have to turn on SNMPv1 or v2c using CLI or the web
interface in order to test this.
Problem: Switch Port Mapper 2.x - Ping Sweep appears to go on forever or hang
Solution:
It's not actually hanging - it's just busy, you need to check
your
Ping Sweep settings before starting a mapping and remember: the
settings are saved specifically for each switch meaning
one switch can have one range being pinged and another
switch another range.
If you are on a small network with a 255.255.255.0 mask,
the default range is 253 hosts - not a problem. But if
you are on a 10.x.x.x network with a 255.0.0.0 mask, the
default range is huge and you have two options: 1. turn
off Ping Sweep or 2. edit the range using the Ping Sweep
editor to match the segments of the network you are
actually using. There can be several ranges in Ping
Sweep, not just one so be sure you are only pinging IP
ranges that are actually used.
Note: the Ping Sweep on/off settings are saved with
the Switch 'Group'. You can edit each switch group by clicking
on Switch Lists, then on Edit Switch Group. A Switch Group is the
unique combination of the IP addresses of the switch and
any secondary servers/routers you are querying.
Problem: The status column is completely empty.
Solution: You have used the Column Order and Visibility Editor to change the columns, but when you did that you removed the ifIndex (Interface Index) column. Open the editor and put the ifIndex column back on the active columns (right) side. Close the editor and remap the switch. This was fixed in v2.35 so that the ifIndex column was made mandatory and cannot be removed from the results grid.
Problem: Switch Port Mapper 2.x - starting the app, exiting, restarting the app one or more times causes computer freeze on Windows 7 - 64 bit.
Solution: Running the app in Safe-Mode works fine. The problem is the video card drivers are out of date. Update the drivers from the video chipset manufacturer instead of through Windows Update. This is a rare problem only reported by one user.
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'NetScanTools Pro', 'NetScanTools Standard', 'NetScanTools LE', 'ipPulse', 'Northwest Performance Software' and 'NetScanTools.com', are trademarks of Northwest Performance Software, Inc.
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