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Scratching the surface of SNMP

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peter.hicks at poggs

Oct 25, 2009, 2:14 PM

Post #1 of 3 (385 views)
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Scratching the surface of SNMP

All,

I am writing an NMS and coming unstuck on a few things:

* Determining which devices are on a port on a device that doesn't
support BRIDGE-MIB::dot1dTpFdbTable, e.g. Cisco 1801 or 877W

* Listing the VRFs and RDs configured on a router, and which
interfaces are a member of which VRF

* Finding out which VLANs are configured on a device, and which are
tagged on a port

Can anyone help me out with their experiences, or in the direction of a
forum more suitable?

Regards,

Peter
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Charlie.Greenaway at btinet

Oct 27, 2009, 1:37 AM

Post #2 of 3 (332 views)
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Scratching the surface of SNMP [In reply to]

Peter,

With regards to point 1. I'm sure that there is a better way of doing this but here is a hack to achieve the same result.
Cross reference the ARP table, IfTable and IP Table. From these you will be able to eliminate the locally configured IP addresses and MAC addresses (the intersection of ARP and IP tables). Whatever is left in the ARP table is what is connected to the interface (intersect with remainder of ARP table and IF table).

Clearly, if there are devices that are bridging only, they will not appear.

Please do keep me posted on how you get on. I'm going to be writing some MPLS/VRF-Lite based tools soon.

Best regards,

Charlie G

Charlie Greenaway - CCIE#11226 (Security/R&S)

Solutions Architect | BT iNet | Tel: +44 (0)1993 885897
Email: charlie.greenaway [at] btinet | Web: www.btinet.bt.com

-------------------------------------------------------------------------------------
Date: Sun, 25 Oct 2009 21:14:15 +0000
From: Peter Hicks <peter.hicks [at] poggs>
To: cisco-nsp [at] puck
Subject: [c-nsp] Scratching the surface of SNMP
Message-ID: <4AE4BFA7.10608 [at] poggs>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

All,

I am writing an NMS and coming unstuck on a few things:

* Determining which devices are on a port on a device that doesn't
support BRIDGE-MIB::dot1dTpFdbTable, e.g. Cisco 1801 or 877W

* Listing the VRFs and RDs configured on a router, and which
interfaces are a member of which VRF

* Finding out which VLANs are configured on a device, and which are
tagged on a port

Can anyone help me out with their experiences, or in the direction of a
forum more suitable?

Regards,

Peter

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peter.hicks at poggs

Oct 27, 2009, 2:28 AM

Post #3 of 3 (334 views)
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Re: Scratching the surface of SNMP [In reply to]

Hi Charlie

Charlie Greenaway wrote:

> Cross reference the ARP table, IfTable and IP Table. From these you
> will be able to eliminate the locally configured IP addresses and MAC
> addresses (the intersection of ARP and IP tables). Whatever is left
> in the ARP table is what is connected to the interface (intersect
> with remainder of ARP table and IF table).

I've already implemented that - great for physical interfaces with an IP
address attached, but it doesn't do what I need for VLAN or SVI
interfaces. All the ARP entries are associated with the SVI - the lack
of dot1dBridgeFdbTable support means I can't tell which physical port a
device is connected to.

Here's an example - I have an 1801 with three unmanaged switches
connected to it, and I can't tell which port on the 1801 a particular
MAC address appears on.

> Please do keep me posted on how you get on. I'm going to be writing
> some MPLS/VRF-Lite based tools soon.

Check out NetHorus - www.nethorus.org - which I am writing. I have a
load of commits to sort out in the coming weeks plus a new layout based
on feedback from people who grok usability.

Regards,

Peter
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