Well, I could be wrong but maybe this is different for various (newer vs.
older as well?) switches and/or different OSes. Leigh Anne did mention this
for the 5000/5500 but just guessing, it looks like Joe's output is from a
4000.
What I do know is that the Cisco Press LAN Switching book supports Leigh
Anne's statement. It goes so far as to mention this specific scenario as a
"gotcha". Of course this book is a little older now, so maybe the newer
product addresses this issue.
My 2 cents!
Rik Guyler
Principal Consultant
Cardinal Solutions Group
-----Original Message-----
From: Matt Holbert [mailto:[EMAIL PROTECTED]]
Sent: Monday, July 10, 2000 6:07 PM
To: [EMAIL PROTECTED]
Subject: Re: Easy Brain Teaser (Switching)
I have to agree with Joe (alhtough not in the same tone). I'm willing to
take it a step further, and say the cable doesn't even have to be pulled
out. As soon as the switch hears the MAC address on a different port, the
CAM table is updated.
Take HSRP for example. If you have two routers connected to the same switch
both running HSRP, if one goes down the other takes over almost immediately.
This means the CAM table must be updated almost immediately as well because
the virtual IP address has the same MAC address.
"Joe Pinkus" <[EMAIL PROTECTED]> wrote in message
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> Leigh Anne,
>
> This is completely false what you have just said, here is the output from
a switch:
>
> 4000-7-1 (enable) sh cam dynam 2/17
> * = Static Entry. + = Permanent Entry. # = System Entry. R = Router
> Entry. X = Port Security Entry
>
> VLAN Dest MAC/Route Des Destination Ports or VCs / [Protocol Type]
> ---- ------------------
> ----------------------------------------------------
> 1 00-50-8b-9b-22-b2 2/17 [ALL]
> Total Matching CAM Entries Displayed = 1
> 4000-7-1 (enable) set cam aging ?
> Usage: set cam agingtime <vlans> <agingtime>
> (agingtime = 0, 15..1000000 seconds, 0 to disable)
> vlans = 1..1005
> An example of vlans is 2-10,1005)
> 4000-7-1 (enable) set cam aging 1 10000
> Vlan 1 CAM aging time set to 10000 seconds.
> 4000-7-1 (enable) sh cam aging
> VLAN 1 aging time = 10000 sec
> VLAN 1003 aging time = 300 sec
> VLAN 1005 aging time = 300 sec
> 4000-7-1 (enable) sh cam dyanm 2/17
> Usage: show cam [count] <dynamic|static|permanent|system> [vlan]
> show cam <dynamic|static|permanent|system> <mod_num/port_num>
> show cam <mac_addr> [vlan]
> show cam agingtime
> 4000-7-1 (enable) sh cam dynam 2/17
> * = Static Entry. + = Permanent Entry. # = System Entry. R = Router
> Entry. X = Port Security Entry
>
> VLAN Dest MAC/Route Des Destination Ports or VCs / [Protocol Type]
> ---- ------------------
> ----------------------------------------------------
> 1 00-50-8b-9b-22-b2 2/17 [ALL]
> Total Matching CAM Entries Displayed = 1
> 4000-7-1 (enable) pull the cable
> Unknown command "pull". Use 'help' for more info.
> 4000-7-1 (enable) 2000 Jul 06 14:22:45 %PAGP-5-PORTFROMSTP:Port 2/17
> left bridge port 2/17
>
> 4000-7-1 (enable) sh cam dynam 2/17
> * = Static Entry. + = Permanent Entry. # = System Entry. R = Router
> Entry. X = Port Security Entry
>
> VLAN Dest MAC/Route Des Destination Ports or VCs / [Protocol Type]
> ---- ------------------
> ----------------------------------------------------
> 4000-7-1 (enable)
>
> Notice that after the cable was pulled, the mac address was purged.
>
> Leigh Anne Chisholm wrote:
>
> > I've seen this "problem" quite often, and it's helpful that you've
brought this up.
> >
> > In the Catalyst 5000/5500 series switch, the MAC address to port mapping
table keeps entries for 5 minutes (or 300 seconds) by default. When you
switch ports (say, moving a server from a test room to the production
location), the table waits the aging time before the old MAC address/port
mapping is removed. This creates the lack of connectivity you reference.
> >
> > The aging of the MAC address to port mapping can really play havoc with
one's mind when the default has been changed to the maximum of 20 minutes
(someone's decided that changing this value will optimize switch and network
performance). This leaves the administrator scratching their heads for 20
minutes wondering why they don't have connectivity.
> >
> > -- Leigh Anne
> >
> > > -----Original Message-----
> > > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
> > > John Neiberger
> > > Sent: Thursday, July 06, 2000 9:05 AM
> > > To: [EMAIL PROTECTED]
> > > Subject: Easy Brain Teaser (Switching)
> > >
> > >
> > > Here's an easy one, because I'm nicer than Chuck. :-) Even though
it's
> > > easy, it's still practical. And for those of you who immediately know
the
> > > answer, let the less experienced people mull this one over for a bit.
> > >
> > > You have a Catalyst 5000 with several servers connected and you've
decided
> > > to rearrange the port assignments. You disconnect one server in
> > > particular
> > > and move it to another port, then quickly discover that it now has no
> > > network connectivity. You attempt to access the network for a couple
of
> > > minutes to no avail. In supreme frustration, you head to the
> > > break room for
> > > coffee and donuts.
> > >
> > > When you come back several minutes later you find that the server now
has
> > > network connectivity and all is well, no problems.
> > >
> > > What is the most likely cause of this behavior and what could you
> > > have done
> > > to remedy the situation immediately?
> > >
> > > Good luck!
> > >
> > > John
> > >
> > >
> > >
> > >
> > >
> > > _______________________________________________________
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