[c-nsp] Lot of input errors on a NPE-G1 interface

[Matlock, Kenneth L]

" hubs, concentrators,  switches, bridges, etc... to this interface
when portfast is enabled, can cause temporary bridging loops."

Those are all Layer 2 devices. A router is a layer 3 device (unless you
explicitly turn bridging on).

Ken Matlock
Network Analyst
303-467-4671
matlockk at exempla.org




-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Chris Gotstein
Sent: Wednesday, May 23, 2012 1:19 PM
To: Gert Doering
Cc: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] Lot of input errors on a NPE-G1 interface

%Warning: portfast should only be enabled on ports connected to a single
host. Connecting hubs, concentrators,  switches, bridges, etc... to this
interface  when portfast is enabled, can cause temporary bridging loops.

My understanding of this was a router would be included as well since
it's used to connect multiple hosts.  I only enable portfast on ports
connected to end-user devices.  I don't see a good reason to enable it
on ports connected to routers, but that's just how it was explained to
me, I very well could be wrong.

On 5/23/2012 1:29 PM, Gert Doering wrote:
> Hi,
>
> On Wed, May 23, 2012 at 01:15:16PM -0500, Chris Gotstein wrote:
>> It's probably not going to address the overrun issue, but from a best

>> practices stand point, it should not be enabled on interfaces that 
>> connected to other connected devices, ie a router or switch.
>
> Uh, so it should only be turned on for switchports that connect to...
> "no device"?
>
> Anyway: right for "to switch", dead wrong for "to router".  It should 
> be turned on for any connection that is known to not go to a switch or

> hub, and doubly so if rapid-pvstp is used (due to TCNs being sent on a

> link flap otherwise, possibly causing stalls elsewhere).
>
> As far as a switch is concerned, a "router" is the same thing as "a 
> host" - it doesn't forward layer2 things, so can't cause a routing
loop.
>
> gert
>

--
---- ---- ---- ----
Chris Gotstein, Network Engineer, U.P. Logon/Computer Connection U.P.
http://uplogon.com | +1 906 774 4847 | chris at uplogon.com
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