How to test ports in a switch?

[Jack Coats]

I have a 24 port switch that belongs to my wife's employer.  It appears to have some 'broken' ports.

How do I test the ports?

It is a Netgear JFS524 ProSafe 24 port 10/100 switch.

I don't think it is managed, and if it is I need to remove any vlan's, etc if there are any.

If you have any special insights, assistance would be appreciated.

... Jack

--

><> ... Jack
Whatever you do, work at it with all your heart... Colossians 3:23
"You don't manage people; you manage things. You lead people." — Admiral Grace Hopper, USN
"If you are not part of the solution, you are part of the precipitate" - Henry J. Tillman
"Anyone who has never made a mistake, has never tried anything new." - Albert Einstein

[Chris McQuistion]

At the lowest level, I would start by just plugging a computer into each port, one at a time and see if you get a link light.  Next, plug two computers into different ports on the switch, with static IP addresses and see if they can ping each other.  Move one of them to a different port and see if the pings continue.  Rinse and repeat.

Chris 

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[Jack Coats]

Some days problems come in faster than I can think them through.

Thanks for helping be a 'distributed brain'. I am obviously being subjected
to DOS attacks :(

Thanks again ... Jack

[Paul Tabolinsky]

Hi Jack
     I was thinking along the same line as Cris was in his reply.  This is a good reason for a couple of those small portable, inexpensive  netbook computers or a couple of small DIY ones.
     Paul T

On Tue, Sep 4, 2012 at 9:32 AM, Jack Coats <ja...@coats.org> wrote:

Some days problems come in faster than I can think them through.

.  .  .  .  cut  .  .  .  .

[Kevin Hart]

My only other thought is to push some heavy load across it. Or across multiple ports. Like try to max out a transfer and see if it dies out. This will take longer of course. The other thing could be make up a 320ft Ethernet cable and see how well it likes the near terminal length. I've seen some ports not like that.  But these are extreme tests IMHO

Sent from my iPhone

[Drew from Zhrodague]

On 9/4/12 9:28 AM, Chris McQuistion wrote:
> At the lowest level, I would start by just plugging a computer into each
> port, one at a time and see if you get a link light. Next, plug two
> computers into different ports on the switch, with static IP addresses
> and see if they can ping each other. Move one of them to a different
> port and see if the pings continue. Rinse and repeat.

I have seen switches that will turn on their link light, even when the
port is not working properly. Sometimes they cheap-out on link detection
in the switch's port, and only test one pair of pins.

I've seen the more strange and confounding behavior from managed
switches - like data goes through, but certain types of traffic get
mangled. With the unmanaged units, either a port (or bank of ports) will
work, or it won't.

Pinging through the switch, as Chris said, is the first thing to test.
Sometimes the connector just needs to be reseated.


--

Drew from Zhrodague
lolcat divinator
dr...@zhrodague.net

[Howard White]

On 09/04/2012 09:17 AM, Jack Coats wrote:
> I have a 24 port switch that belongs to my wife's employer. It appears
> to have some 'broken' ports.
> How do I test the ports?
>
> It is a Netgear JFS524 ProSafe 24 port 10/100 switch.
>
> I don't think it is managed, and if it is I need to remove any vlan's,
> etc if there are any.
>
> If you have any special insights, assistance would be appreciated.
>
> ... Jack
>

Others have submitted meaningful tests. Here is one _not_ to do in a
production environment: plug both ends of a patch cable into two ports
on the same [switch | network]. This results in a network race
condition that generally causes the network to go completely
jabberwocky. Some newer, smarter switches are able to detect this
condition. I don't seem to be in the price range of the switches with
this capability.

Howard

[Curt Lundgren]

Amusingly enough, on certain inexpensive HP managed switches, you reset the switch configuration by plugging a cable into ports 1 and 2.  The 1700 and 1800 series are the ones I've used that take this approach.  The lesson to learn is never to set up a trunk using ports 1&2 as members.  One power reset and you have a stupid switch.

Curt

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[Curt Lundgren]

In direct response to Howard's comment, plugging a cable into two ports will cause a broadcast storm.  Many managed switches allow rate limitations to be set up on broadcasts, this can avoid the jabberwocky condition inexpensive switches go into.  (Gee, why is there a steady 10% bandwidth at all times?!!)

Curt

[Blake Dunlap]

On Tue, Sep 4, 2012 at 12:01 PM, Curt Lundgren <veri...@gmail.com> wrote:

In direct response to Howard's comment, plugging a cable into two ports will cause a broadcast storm.  Many managed switches allow rate limitations to be set up on broadcasts, this can avoid the jabberwocky condition inexpensive switches go into.  (Gee, why is there a steady 10% bandwidth at all times?!!)

Curt

Friends shouldn't let friends melt their networks by broadcast storm...

You can get even real fully managed cisco switches from back in the day for like $10 to $30 off of ebay. If you aim lower, the cost drops accordingly. That said, I think even best buy consumer switches do at least 802.1D as of years ago.

-Blake 

[Howard White]

On 09/04/2012 12:01 PM, Curt Lundgren wrote:
> In direct response to Howard's comment, plugging a cable into two ports
> will cause a broadcast storm. Many managed switches allow rate
> limitations to be set up on broadcasts, this can avoid the jabberwocky
> condition inexpensive switches go into. (Gee, why is there a steady 10%
> bandwidth at all times?!!)
>
> Curt

Thank you for correcting me on the exact term. Bad news either way...

Howard

[Toth, Csaba]

We must add, that Chris's tests are only basic tests. Unfortunately some interfaces can be faulty even if Chris's tests work. They can flood the ethernet network with faulty packets, while you still have ping and connection.
But in that case the high throughput commands suffer a lot from bogus packets.
I've seen that in dormitories in Hungary. To track down such maybe not easy. Although in Linux you can see the number of dropped packets on the interface. If that number is very high, then there's some evil interface connected onto the same ethernet network.

Csaba
________________________________________
From: nlug...@googlegroups.com [nlug...@googlegroups.com] On Behalf Of Drew from Zhrodague [drewzh...@zhrodague.net]
Sent: Tuesday, September 04, 2012 7:59 AM
To: nlug...@googlegroups.com
Subject: Re: [nlug] How to test ports in a switch?

[Jack Coats]

Thanks to everyone. ...

This is a 'real soon now' project, because this old Netgear 24port
10/100 switch is connecting many different points in one building.
But I have been trying some ports just to get 2 or 3 'working' and it
has become problematic.

I do have a 'good' link to our XP server (running ICS) and a Sprint
Aircard. So I can ping that and just unplug wires for a few minutes
to test each port using my laptop.

Even during the 'heavy season' there are 5 or 7 computers, one
copier/printer that is leased hooked to it. So for a 'commercial
switch' the traffic is laughingly slow.

But when working from hand-me-down equipment from the Girl Scouts, we
do what we can to keep it running. Just mapping the 'bad' ports and
knowing for sure they are not good, and which ones really do work 'ok'
is a good first step in makeing 'junk' somewhat usable.

I would like for this to be a good 16 port switch, but speinding cash
is not in the cards, at least not on networking.

Personally I would give a lot to have just a good wired network out
here. ... I am in the slow process of upgrading the wireless network
using Ubiquiti equipment rather than Walmart Networking grade
equipment. But whenever I do, it is one step forward, two steps back
reciently. Eventually I will prevail. (Oh yes, the Ubiquiti equipment
is coming out of my pocket, not GS).

Thanks for all the support (and even listening to my whining, I am
trying to keep that down).

... Later friends, Jack