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tracing a mac address?

 
 
dexx
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      05-25-2005
I remember once seeing an IOS command that, given a mac address, would
trace that address through the network to its end point. For example; a
PC is connected to port 8 of a 2950 switch. The 2950 uplinks to a 3550
which, in turn, uplinks to a core 6509. From the 6509 i can issue a
command which shows me all intermediary devices and shows me the end
switch and which port the target device connects to. Does anyone know
the syntax for this command?

 
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Walter Roberson
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      05-25-2005
In article <(E-Mail Removed) .com>,
dexx <(E-Mail Removed)> wrote:
:I remember once seeing an IOS command that, given a mac address, would
:trace that address through the network to its end point. For example; a
C is connected to port 8 of a 2950 switch. The 2950 uplinks to a 3550
:which, in turn, uplinks to a core 6509. From the 6509 i can issue a
:command which shows me all intermediary devices and shows me the end
:switch and which port the target device connects to. Does anyone know
:the syntax for this command?

If it can be done at all, it would be via cdp .

In general, it can't be done with much degree of certainty.
And 75% of the time, when you go to look for the information,
it isn't there anymore.
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Hansang Bae
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      05-25-2005
dexx wrote:

> I remember once seeing an IOS command that, given a mac address, would
> trace that address through the network to its end point. For example;
> a PC is connected to port 8 of a 2950 switch. The 2950 uplinks to a
> 3550 which, in turn, uplinks to a core 6509. From the 6509 i can
> issue a command which shows me all intermediary devices and shows me
> the end switch and which port the target device connects to. Does
> anyone know the syntax for this command?


You are probably thinking of L2trace. But there are severe
limitations. We have asked Cisco for such a tool though. They have it
for multicasts (mapping out the MC tree) so it would be pretty easy to
convert it to unicast traffic.

In the tool, I wanted to see L3 *and* L2 port information, associated
error counters, and it *had* to account for redundant paths since every
link on our network is redundant. Getting cef exact-route info was
considered gravy.

--

hsb


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CiscoTech
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      05-25-2005
show mac-address-table address xxxx.xxxx.xxxx

Walter Roberson wrote:
> In article <(E-Mail Removed) .com>,
> dexx <(E-Mail Removed)> wrote:
> :I remember once seeing an IOS command that, given a mac address, would
> :trace that address through the network to its end point. For example; a
> C is connected to port 8 of a 2950 switch. The 2950 uplinks to a 3550
> :which, in turn, uplinks to a core 6509. From the 6509 i can issue a
> :command which shows me all intermediary devices and shows me the end
> :switch and which port the target device connects to. Does anyone know
> :the syntax for this command?
>
> If it can be done at all, it would be via cdp .
>
> In general, it can't be done with much degree of certainty.
> And 75% of the time, when you go to look for the information,
> it isn't there anymore.

 
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Seppo Mannisto
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      05-25-2005
On 2005-05-25, Walter Roberson <(E-Mail Removed)-cnrc.gc.ca> wrote:
> In article <(E-Mail Removed) .com>,
> dexx <(E-Mail Removed)> wrote:
>:I remember once seeing an IOS command that, given a mac address, would
>:trace that address through the network to its end point. For example; a
>C is connected to port 8 of a 2950 switch. The 2950 uplinks to a 3550
>:which, in turn, uplinks to a core 6509. From the 6509 i can issue a
>:command which shows me all intermediary devices and shows me the end
>:switch and which port the target device connects to. Does anyone know
>:the syntax for this command?
>
> If it can be done at all, it would be via cdp .
>
> In general, it can't be done with much degree of certainty.
> And 75% of the time, when you go to look for the information,
> it isn't there anymore.


It can be done but the usual output is something like this:

sw2#traceroute mac 0011.43a4.dd3a 0020.6b51.2455
Source 0011.43a4.dd3a found on sw1
1 sw1 (2.2.2.2) : Fa0/11 => Fa0/24
2 sw2 (2.2.2.3) : Fa0/23 => Gi0/1
l2trace error response received : 7 from 2.2.2.4
Unable to locate port for src 0011.43a4.dd3a on sw3 [2.2.2.4].
Layer2 trace aborted.


--
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Chris Ames
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      05-25-2005
On 24 May 2005 18:55:40 -0700, "dexx" <(E-Mail Removed)> wrote:

>I remember once seeing an IOS command that, given a mac address, would
>trace that address through the network to its end point. For example; a
>PC is connected to port 8 of a 2950 switch. The 2950 uplinks to a 3550
>which, in turn, uplinks to a core 6509. From the 6509 i can issue a
>command which shows me all intermediary devices and shows me the end
>switch and which port the target device connects to. Does anyone know
>the syntax for this command?


I don't know about the 6500 series, as I don't have access to one at
the moment, but on 3750s and 2950s, use trace mac:

3750g.core#trace mac 0004.23a8.e67c 0800.46cf.1b27 vlan 70
Source 0004.23a8.e67c found on 3750g.core
1 3750g.core (10.8.5.1) : Gi2/0/24 => Gi2/0/10
2 2950t-1.a (10.8.5.5 : Fa0/1 => Fa0/22
3 2950t-1.d (10.8.5.63) : Gi0/2 => Gi0/1
4 2950t-2.d (10.8.5.64) : Gi0/2 => Fa0/14
Destination 0800.46cf.1b27 found on 2950t-2.d

 
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H.U.A. Koers
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      05-26-2005
With the lack of such a command I've made a PERL script to do this job,
input in the script is:

- MAC address
- VLAN number
- List of IP numbers of Cisco switches w/ uplinks (these ports should not be
tested) in a textfile, such as:

192.168.1.1
Gi1/1 Gi1/3
192.168.1.2
Gi1/2 Gi1/3
192.168.1.5
1/2 1/3

IOS and CatOS switches use different portnames, Gi3/1 (4506) and 1/1 (6509).

The script is based on SNMP read-only and searches the mac-address-table for
the specific MAC/VLAN. Some conversions have to be made (hex MAC to decimal
notation). The script also provides a conversion for ifindex to readable
(Gi1/1 or 6/5) portnumbers. Works like a charm for me.

Also problems like duplicate MAC can be found easily, the script searches
all given switches for the MAC/VLAN. Only caveat of the script is the .txt
file which must be kept uptodate with the actual topology.

I'm using the script with Activestate PERL v5.6.1 build 635, MS C++ 6.0
(nmake) and NET-SNMP 4.1.2 library on a W2k station.

Arjen

"dexx" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
> I remember once seeing an IOS command that, given a mac address, would
> trace that address through the network to its end point. For example; a
> PC is connected to port 8 of a 2950 switch. The 2950 uplinks to a 3550
> which, in turn, uplinks to a core 6509. From the 6509 i can issue a
> command which shows me all intermediary devices and shows me the end
> switch and which port the target device connects to. Does anyone know
> the syntax for this command?
>



 
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