IP Address and DNS Name missing on some ports
Creates web pages that show information about Ethernet switches.
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Hi,
Firstly I'd like to say thanks for putting the time into developing such a
useful tool. I'm having a small problem with switchmap not showing IP Address
and DNS names form some switch ports on our switches. I noticed an earlier
post which had to do with the entry not being in the MAC table (https://sourc
eforge.net/projects/switchmap/forums/forum/378009/topic/3266664) (sourceforge.net) but I am
running switchmap during the day and still not seeing any hostnames / IP
Addresses. Our edge switches are 2975s but go back to 6501s (which I am
querying via switchmap so should be getting the layer 3 information).
Has anyone else had a similar situation or able to suggest something I can
try?
I'm not sure if this is relevant, but I have just noticed the "What (via CDP)"
column is blank, though CDP is enabled and working on all switches. Some ports
are showing IP Address and HostName information. In most cases the "What (via
CDP)" column is blank when hostnames / IP Addresses are present.
Are you running GetArp.pl regularly?
GetArp creates/updates a file named MacList. Can you find that file? On Linux,
it may be in /var/local/switchmap.
The MacList file is a simple text file. You can look at it with a text editor.
The format is <mac> <ip> <timestamp>. I'll bet the file doesn't contain
entries for the MACs/IPs that are missing. If so, then perhaps you aren't
feeding GetArp.pl enough routers. You need to give GetArp a list of routers
that covers all your networks, so that the ARP caches from the routers will
sometimes have an entry for every IP address on your networks.</timestamp></ip></mac>
The "What (via CDP)" values come from the contents of the CDP tables in the
switches. If CDP is blocked between any of your devices, the CDP data might
not be available. Please try running a "show cap neighbors" command on one of
the problem switches. If SwitchMap can't read the CDP table from a switch, you
won't get any values in the column, for the whole switch. Perhaps SwitchMap
can't read the CDP table because the switch blocks reading of CDP table via
SNMP - you can tell a Cisco to not allow reading of individual tables. If you
can do a "show cdp neighbors" command on a given switch and see information
about it's neighbors, then SwitchMap should be able to get the same CDP
information from the switch.
Does SwitchMap get CDP information from any of your switches?
On switches that don't have the CDP information that you expect, does
SwitchMap show CDP information for some of the ports and not others, or does
it show no CDP information at all?
kI added a line to the prefix-list on Hope this helps, and Please let me know
if this helps or if I can clarify anything.
You can turn on logging to see what SwitchMap is doing. If you run SwitchMap
with a command like
SwitchMap.pl -d 7 -f aabbcc.xxx
then program will run normally, but process only the switch named aabbcc.xxx,
to limit the volume of log messages. As a side effect it'll log informational
messages at level 7, which is detailed enough to show SNMP table read
attempts. It'll write a file named SwitchMap.log in the current directory. The
log file will tell you if SwitchMap is trying to get CDP information from the
switch. That might help you figure out what's going wrong.
Please let me know if this helps.
Ooops, in my last post, It should've read "show cdp neighbors", not "show cap
neighbors", and just ignore the link that starts "kl"
Thanks for the detailed reply - that certainly gives me quite a bit to look
at.
I've found MacList - it has some entries but not as many a I would expect
(about 20). One thing I notice about the file is that is has not been updated
since the afternoon of the 13th (2 days ago). I can't see anything wrong with
the permissions of the file (the webserver has modify access) so I'm not sure
if the webserver is not updating it or the information is not getting to it.
I am getting cdp information from all switches - show cdp neighbours shows all
neighbouring switches. One thing I did notice is that I had the 2 core (layer
3) switches listed under switches - I have moved these 2 routers as they would
be the devices that have the most arp cache entries (if I am reading the
entries in ThisSite.pm correctly). I will let it run through a few collection
cycles and see if this makes any difference.
Moving the layer 3 switches into the routers section seems to have done the
trick. I'm now seeing IP and host name information for all devices on my core
switches. I'm not seeing any info from my branch sites (they are also using
layer 3 switches). Would there be any negative performance implications (or
any other issues) for moving all layer 3 switches to routers rather than the
switches section of ThisSite.pm?
Ok, I think I understand your issue. Perhaps the README file could be more
explicit about this. You have to run GetArp.pl regularly to keep the MacList
file up to date. I run it once an hour. I run SwitchMap once a day. The GetArp
program gets ARP caches from routers, and updates the MacList file. That's all
it does. SwitchMap gets almost all the data that you see in the web pages from
the switches, and uses the MacList data to fill in the IP address columns, and
with the IP address, the DNS columns.
The list of routers is used by GetArp. The list of switches is used by
SwitchMap. Only layer 3 devices should be in the routers list, others won't
hurt, but GetApr will waste time trying to get ARP data from devices that
don't have ARP data.