From: Kurt Kruegel (kurt@cybernex.net)
Date: Sat Oct 11 2003 - 10:58:45 GMT-3
i'd like to ask a question. regarding trunk
we have a mix of 3500xl's and 3550's
recently a normal ethernet host was plugged into a switchport
on a 3548xl that was left switchport mode trunk.
chaos ensued.
there were reports of a general network slowdown.
i didn't figure it out until someone cane to me about a new host added to
our datacenter
that didn't come up. when i looked at the config, i noticed that trunk was
left configured.
also saw something like 22mbit output on the port and i think it was
flashing yellow.
was the slowdown caused by a "spillover" of trunk traffic into a non-trunk
port ????
----- Original Message -----
From: "Kenneth Wygand" <KWygand@customonline.com>
To: "Hunt Lee" <hunt_lee@bigpond.net.au>; <ccielab@groupstudy.com>
Sent: Saturday, October 11, 2003 1:26 AM
Subject: RE: switchport command
> Lee,
>
> Yes, "switchport mode dynamic desirable" tells the port to send DTP frames
(Dynamic Trunking Protocol) to the other switch requesting that a trunk be
dynamically setup. If the other side is listening to DTP packets (set to
AUTO or DESIRABLE), the trunk will form. Also, if the other side is set to
ON, it will not use the DTP packets but will automatically be a trunk
because it's "nailed on" at the remote end.
>
> Once the port becomes a trunk, the "switchport access vlan 120" command
has no effect. If the switchport does NOT become a trunk, it will be an
access port on vlan 120.
>
> The configuration you've provided essentially says "Try to become a trunk
port which will forward all VLANs by default... if you cannot become a trunk
port, you will be an access port - if you do in fact become an access port,
operate on VLAN 120". It's sort of a fallback, for lack of a better term.
>
> Am I clear in my explanation? If not, please let me know and I'll
elaborate further.
>
> Thanks!
> Ken
>
> -----Original Message-----
> From: Hunt Lee [mailto:hunt_lee@bigpond.net.au]
> Sent: Sat 10/11/2003 12:29 AM
> To: ccielab@groupstudy.com
> Cc:
> Subject: switchport command
>
>
>
> Hi Group,
>
> Can someone please explain to me when one will use the following command?
>
> int fa0/6
> switchport access vlan 120
> switchport mode dynamic desirable
>
> And on my practice exerices, they pretty much use these on all the
switchports, including ones that are for connecting to routers and
workstations.
>
> What I don't understand is, isn't the dynamic desirable command will get
the switchport to try to neogotatie and become a trunk? If it is the case,
why using it with switchport access vlan command ?
>
> And when would you use the switchport mode dynamic desirable command?
>
> Any help would be greatly appreciated.
> Lee
>
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