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Today's Topics:
1. Re: Question about restricting SNMP access to a router - user
only needs ARP table (Oliver Gorwits)
2. Multiple interfaces on routers (Hans Erasmus)
3. Re: Multiple interfaces on routers (Oliver Gorwits)
4. Re: Multiple interfaces on routers (Hans Erasmus)
--- Begin Message ---
Hi Andy
I guess one way would be to implement an SNMP "view" on the Juniper
router which is sort of like an ACL for branches of the SNMP tree.
However Netdisco will want to query a bunch of OIDs as well as just the
ARP table.
You could see these OIDs by running an arpnip in debug (-DI) mode.
Netdisco will also want to have discovered the device before pulling the
ARP table, and I'm not sure how you'd do that without opening lots more
OIDs.
There is also the "sshcollector" part of Netdisco which allows gathering
of ARP table by any means, and injecting that into Netdisco to be
associated with an already-discovered device. This might provide another
way to get the data.
Just some starting thoughts, though....
regards,
oliver.
On 2017-08-18 17:31, Andy Ruhl wrote:
I'm really not that skilled with SNMP, I'm hoping someone can point me
in the right direction.
We have a user that we provide layer 2 links to that has a lot of
switches and he has his own Netdisco server.
He needs the ARP info to be able to relate a switch port to an IP.
Is there a way to give him an SNMP string and restrict him to ARP info
only? If we give him regular read access to the router (Juniper), he
will see a lot of stuff that he doesn't need to know.
Or, is there an alternate way that Netdisco can collect ARP info other
than getting it from the router?
Thanks.
Andy
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--- End Message ---
--- Begin Message ---
Hi All
I am getting an unwanted result whilst scanning our network. I know
(practically) why this happens, but I still don't know how to fix it.
When a router comes up that has more than one interface (our user backbone
has 40 x /31's), netdisco will list that device as discovered 40 times. Is
there any way (a script perhaps) in which we can tell netdisco that it is
the same device all along? Maybe have some sort of intelligent "check"
whether the device discovered has the same name or any other details as any
of the devices in the list already, and then flag it and ignore it from
there? Just a thought.
Regards
Hans
--- End Message ---
--- Begin Message ---
Hi Hans
On 2017-08-22 06:40, Hans Erasmus wrote:
When a router comes up that has more than one interface (our user
backbone has 40 x /31's), netdisco will list that device as discovered
40 times.
We have started to look at this issue, but are being cautious in
automatically de-duplicating in case there are scenarios where multiple
devices should remain.
Please can you tell me what the Duplicate Devices report (in the Admin
menu) shows? Are all the duplicates listed there?
Also, can you let me know why you think "practically" this is happening?
Finally, are you using VRFs?
Many thanks, and apologies for the hassle this is causing.
regards,
oliver.
Is there any way (a script perhaps) in which we can tell
netdisco that it is the same device all along? Maybe have some sort
of intelligent "check" whether the device discovered has the same name
or any other details as any of the devices in the list already, and
then flag it and ignore it from there? Just a thought.
Regards
Hans
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--- End Message ---
--- Begin Message ---
Hi Oliver
No need to apologise. This is something one of our guru's has been seeing
for the past 10 years, and his fix was to assign a type of primary key to
the device once it is discovered. I will get more detail on it and post it
if you are interested. So the behaviour is not new, and therefore not
surprising. It is just way out of my league to even try and attempt a fix
for this.
> Please can you tell me what the Duplicate Devices report (in the Admin
menu) shows? Are all the duplicates listed there?
Well, I see a lot of duplicates on this list (293 to be exact but the
discovery is still running) like our PC LAB routers which have multiple
interfaces with multiple subnets connected to it. For instance:
1 x /27 containing the Switch IP segment (SW MGMT)
1 x /24 containing the LAB PC segment (End Users)
1 x /31 containing the Uplinks to the User Backbone
1 or 2 (sometimes more) /30 interconnects between LAB routers to ensure
redundancy (multiple paths).
> Also, can you let me know why you think "practically" this is happening?
Well, in layman's terms, what happens is that as Netdisco goes through the
network whilst discovering, it will come across an IP of say 1.1.1.1 on a
router. This IP could possibly be the gateway for 1.1.1.0/24. Now, taking
the example above, let say this /24 is the end-user segment. This same
router could possibly contain, like in our case, a different routed segment
to service the switch segment. Let call this 1.1.2.0/27. So the router must
have 1.1.2.1 configured as the gateway so the switches knows where to go.
Only using these two segments as an example, we can clearly see that one
router could contain two different network segments and act as a Gateway
for both, and the one segment will not necessarily know about the other.
This helps in containing outages created by loops etc. btw. In the eyes of
Netdisco, these are two totally different devices, as these two segments do
not overlap, or are not part of one another in any shape or form. And these
two segments could have been physically living across campus from each
other. So Netdisco (and any other discoverer worth it's salt) would handle
these segments separately. It will add 1.1.1.1 as a device, and add
1.1.2.1 as a device. But in reality, it is the same device. So maybe
netdisco could, when it discovers a new segment, first inspect whether
anything on that segment has been found on any of the already discovered
device's address tables, and only append the list on that discovered
device, not add a new device, I don't know? Just throwing out ideas here.
To answer your last question, no, we do not make use of any VRF's.
Sorry if this explanation is not explanatory enough.
Regards
Hans
On Tue, 22 Aug 2017 at 08:44 Oliver Gorwits <[email protected]> wrote:
> Hi Hans
>
> On 2017-08-22 06:40, Hans Erasmus wrote:
> > When a router comes up that has more than one interface (our user
> > backbone has 40 x /31's), netdisco will list that device as discovered
> > 40 times.
>
> We have started to look at this issue, but are being cautious in
> automatically de-duplicating in case there are scenarios where multiple
> devices should remain.
>
> Please can you tell me what the Duplicate Devices report (in the Admin
> menu) shows? Are all the duplicates listed there?
>
> Also, can you let me know why you think "practically" this is happening?
>
> Finally, are you using VRFs?
>
> Many thanks, and apologies for the hassle this is causing.
>
> regards,
> oliver.
>
> > Is there any way (a script perhaps) in which we can tell
> > netdisco that it is the same device all along? Maybe have some sort
> > of intelligent "check" whether the device discovered has the same name
> > or any other details as any of the devices in the list already, and
> > then flag it and ignore it from there? Just a thought.
> >
> > Regards
> >
> > Hans
> >
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