From: Church, Chuck (cchurch@netcogov.com)
Date: Fri Sep 30 2005 - 13:04:55 GMT-3
VTP doesn't have anything to do with how switches populate their layer 2
forwarding table. All switches and bridges (non-Cisco also) work by
learning MAC addresses and ports they're seen on. Say I'm a workstation
attached to port 3/1 on switch A, and switch A has a connection to
switch B (port 1/1 on each side). Workstation B is attached to port 5/1
on SwitchB. All ports in same VLAN. If I send a broadcast, switch A
will associate my mac address with it's port 3/1. Switch B will see the
broadcast, and associate it's port 1/1 with my MAC address. If
Workstation B responds to my broadcast, Switch B will associate
Workstation B's MAC address with it's port 5/1. Switch A will associate
Workstation B's MAC address with it's port 1/1 (the connection to Switch
B). Remember, CAM/MAC tables are always locally significant.
WorkstationA----3/1(SwitchA)1/1---------1/1(SwitchB)5/1----WorkstationB
Chuck Church
Lead Design Engineer
CCIE #8776, MCNE, MCSE
Netco Government Services - Design & Implementation
1210 N. Parker Rd.
Greenville, SC 29609
Home office: 864-335-9473
Cell: 703-819-3495
cchurch@netcogov.com
PGP key: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x4371A48D
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Deep Ratan
Sent: Friday, September 30, 2005 11:26 AM
To: Sheahan, John
Cc: ccielab@groupstudy.com
Subject: Re: layer-2 interview question
John,
Your reply answers my question. I didn't know layer-2 information is
propagated via VTP across the entire VLAN domain.
In reiteration: If I do a "show cam dyn" on a switch, I'll see the mac
address of an end user machine that is connected 10 switches away,
assuming
both switches have the same VLAN, VTP is working, etc?
On 9/30/05, Sheahan, John <John.Sheahan@priceline.com> wrote:
>
> "sh cam dyn" will show you all mac addresses that the switch knows
about
> from a layer two persective. That includes machines plugged into hubs
> that are plugged into switch. It will also know about mac addresses on
> other switches that are trunked to the switch.
>
> If you are running IOS, you can easily sort through 10,000 mac
addresses
> with the following command:
>
> "sh mac-address-table | begin 0009.b7e0.c2e"
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Deep Ratan
> Sent: Friday, September 30, 2005 11:04 AM
> To: ccielab@groupstudy.com
> Subject: Re: layer-2 interview question
>
> does "show cam" display mac address of A) machines directly connected
to
> the
> switch ports of the switch or B) machines on all vlans across all
> switches
> in those vlans?
>
> If B) is true, the output of that command could have 10,000 entries.
>
> On 9/30/05, Adam S. Roth <adam@therothfamily.net> wrote:
> >
> > Show cam
> >
> > This email message and any attachments are intended for the use of
the
> > addressee(s) indicated above. Information that is privileged or
> otherwise
> > confidential may be contained herein. If you are not the intended
> > recipient(s), you are hereby notified that any dissemination,
review,
> or
> > use
> > of this message, documents, or information contained herein is
> strictly
> > prohibited.
> >
> >
> >
> >
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> > Deep
> > Ratan
> > Sent: Friday, September 30, 2005 10:48 AM
> > To: ccielab@groupstudy.com
> > Subject: layer-2 interview question
> >
> >
> > Hi Everyone,
> > Sorry to ask a networking-101 question but being a WAN guy, I
haven't
> been
> > working with switches in the past few years. An interviewer asked me
> this
> > question, "If I give you a MAC address that is causing a broadcast
> storm,
> > how will you locate the culprit in a switched environment that has
> several
> > dozen switches and routers?"
> >
> > I replied, "You'll need to give me a layer-3 address so I can trace
it
> to
> > the right switch/router and then look up the ARP table to see on
what
> port
> > the offending machine lives" The interviewer didn't like the answer.
> In
> > retrospect, I should probably have said, "A broadcast storm renders
> the
> > network unusable, so I'll start with looking at my network
management
> > station to see what LAN segment is giving off a critical alarm"
> >
> > Anyway, my question to members of groupstudy is this: In an
> environment
> > with
> > several dozen switches, if you're given just a MAC address, can you
> find
> > out
> > where the machine lives?
> >
> > thanks, Deep
> >
> >
>
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