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Old 05-21-2010, 09:34 AM   #1
Norwood
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Help solve a friendly bet - Why do some Ethernet switches separate some ports?


As you can see in this picture, I have this simple little switch on my desk.

Why is port 5 separated from the other 4 ports?
 
Old 05-21-2010, 10:59 AM   #2
ilikejam
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It's the uplink (to another switch). Switch-switch (uplink) connections require a crossover cable, or in this case an auto-sensing switch port; the rest are normal straight-through connections.

Dave
 
Old 05-21-2010, 11:08 AM   #3
Tornado_Shanks
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My guess would be that port 5 is the only crossover autosensing port
 
Old 05-21-2010, 11:29 AM   #4
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Just to the right of the port it says "auto uplink cross-over or straight-through" (partly said with symbols).

There is probably nothing more special about it for uplink purposes than the fact that it is autosensing for crossover. It can be used for non uplink and another port could be used for uplink provided the uplink doesn't need crossover autosense at this end.

Last edited by johnsfine; 05-21-2010 at 11:32 AM.
 
Old 05-21-2010, 12:00 PM   #5
bstafford51
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switch port 5

All 5 switch ports on that switch will auto connect if memory serves me right. Port 5 is separate because of it costs less to put a standard 4 port and one 1 port than pay for a special 5 port component.

Just verified my previous post. The 8 port model uses two 4 port components, the 16 port uses four 4 port components. All ports are auto crossover.

Last edited by bstafford51; 05-21-2010 at 12:07 PM.
 
Old 05-21-2010, 12:30 PM   #6
tommylovell
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And to add to what was already said before, and not necessarily the case with your Netgear switch...

Small switches generally fall into a class called "desktop" or "workgroup" switches. They are usually small in size and port count, sit in an office environment (not a closet), and are relatively inexpensive.

I can't find a good link to describe the difference between "desktop" and "workgroup" switches versus "enterprise" and "departmental", but basically, "enterprise" and "departmental" switches can be interconnected or cascaded. They are smart devices and will cache the source MAC address and port each incoming packet is received on. The "arp cache" can generally hold at least a few thousand entries. When a packet is received that is destined for one of the cached addresses, the switch knows what port to send it out on. If it does not have an entry, it is send out on all ports (except the one it was received on). "desktop" and "workgroup" switches sometimes have limitations.

As you can imagine, there is a cost associated with the "arp cache" or "MAC Database" mechanism. So to reduce cost, workgroup switches were created. The biggest cost saving was to eliminate the large arp cache found in their larger cousins and instead just remember one MAC address per port (usually the last source MAC address received). The uplink port does not remember any MAC addresses, so any packet whose destination MAC address is not known will always go out the uplink port. This means that you can't (actually shouldn't) use a non-uplink port to connect to another switch.

That being said, some cheap workgroup switches can cache multiple MAC addresses, so there is no restriction on how you interconnect switches (as long as you have no loop in your topology - Google "Spanning Tree" protocol). It's sometimes difficult to dig out this info, but not always. So it really depends on the switch. The newer ones tend to have adequate arp caches; most old switches have the one-per-port cache.

Example:
http://www.netgear.com/Products/Swit...Specifications - Netgear GS605 has a spec "MAC address database: 4,000 ".

The old Linksys switches had just one MAC per port.

Yours looks fairly old. You'd have to find its specs on the Netgear site to see how capable it is.

Hope this makes sense and helps.
 
Old 05-21-2010, 01:02 PM   #7
fruttenboel
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Quote:
Originally Posted by Norwood View Post
As you can see in this picture, I have this simple little switch on my desk.

Why is port 5 separated from the other 4 ports?
Netgear is NOT a feeble brand.

In your case, it is outdated equipment. The 5th port is for connecting to a router or another switch. Proper switches of this time are auto MDI so they 'see' the polarity of the cable and make auto adjustment. My Longshine switches are all auto MDI, so you can use any cable on any port for any connection. Other brands will have similar properties, I guess. But those are more expensive.

See http://cgi.ebay.nl/ws/eBayISAPI.dll?...STRK:MESELX:IT
 
Old 05-21-2010, 02:22 PM   #8
Norwood
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I never said anything about it being feeble. We use Netgear all over the place here at work. It's all over our data center, wire-closet etc.

When I said "I have this small switch here" I meant the size of it.

I guess I'm just used to running cable off of stacks of fourteen 84 port modular inifiband switches and consider a desktop 5 porter to be small in size.

If you work for Netgear, I hope I didn't offend you. We love your products, nothing wrong with them at all...It's just a small switch I have on my desk that one of the engineers here said the 5th port is for "the internet"...as if it's a router. I told him it's for uplinking to sister switches...etc.

Again, apologies if I offended you. I just think it's a small router...but to each his own.
 
Old 05-21-2010, 03:17 PM   #9
fruttenboel
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Quote:
Originally Posted by Norwood View Post
I never said anything about it being feeble. We use Netgear all over the place here at work. It's all over our data center, wire-closet etc.

When I said "I have this small switch here" I meant the size of it.

I guess I'm just used to running cable off of stacks of fourteen 84 port modular inifiband switches and consider a desktop 5 porter to be small in size.

If you work for Netgear, I hope I didn't offend you. We love your products, nothing wrong with them at all...It's just a small switch I have on my desk that one of the engineers here said the 5th port is for "the internet"...as if it's a router. I told him it's for uplinking to sister switches...etc.

Again, apologies if I offended you. I just think it's a small router...but to each his own.
Hey hey hey,

We're both penguinistas. Nobody is angry at anyone else.

As a matter of fact, I am the dutch distributor for Longshine ICT equipment. Netgear is 'the competition'. Netgear have always made fine and innovative products. Like a router with two WAN ports and a load balancing firewall.. I wish Lomngshine would have such one in the assortment right now.

The switch on your desk is an oldie. Still going strong. Nowadays these 5 port switches cost something like 10 euro (consumer price including all taxes). When your one was new, it cost at least ten times as much. But its quality is obvious. Still going strong...
How do you power it? If it's on a wall wart transformer, throw it out of the window and install a cheap wall wart switch mode power supply. These are 90% better in power efficiency.
 
Old 05-21-2010, 04:21 PM   #10
jefro
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It is for uplinks to other switches. (but I can't see the photo)
 
Old 05-21-2010, 05:30 PM   #11
jschiwal
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Moved: This thread is more suitable in
General and has been moved accordingly to help your thread/question get the exposure it deserves.
ot a linux question.
 
Old 05-21-2010, 05:30 PM   #12
jschiwal
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Wireless or stubby finger caused double posting.

Last edited by jschiwal; 05-21-2010 at 05:55 PM.
 
Old 05-24-2010, 07:18 AM   #13
Norwood
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Quote:
Originally Posted by fruttenboel View Post
Hey hey hey,

We're both penguinistas. Nobody is angry at anyone else.

As a matter of fact, I am the dutch distributor for Longshine ICT equipment. Netgear is 'the competition'. Netgear have always made fine and innovative products. Like a router with two WAN ports and a load balancing firewall.. I wish Lomngshine would have such one in the assortment right now.

The switch on your desk is an oldie. Still going strong. Nowadays these 5 port switches cost something like 10 euro (consumer price including all taxes). When your one was new, it cost at least ten times as much. But its quality is obvious. Still going strong...
How do you power it? If it's on a wall wart transformer, throw it out of the window and install a cheap wall wart switch mode power supply. These are 90% better in power efficiency.
Yeah, we pulled them out of a few conference rooms as spares so I decided to just toss one on my desk. I've got a laptop, my desktop and my little netbook hooked to it. Out of curiosity, having not seen/used one in so long I look up the price and I think they are basically free or something like $5.00 after instant rebates etc at places like newegg.com

But it's just a standard wall wart...but I'm not going to spend any money on I've got a three port jack under my desk anyway, I just got tired of running my netbook through the ethernet port on the back of my Avaya 9620 phone so I threw that there. As soon as this is needed somewhere in the company (for Lord knows what heh) it'll be deployed that way.
 
Old 05-24-2010, 09:29 AM   #14
catkin
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Quote:
Originally Posted by fruttenboel View Post
If it's on a wall wart transformer, throw it out of the window and install a cheap wall wart switch mode power supply. These are 90% better in power efficiency.
Thanks for the heads up
 
  


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