Excessive collisions and slow speed with 10Mbps hub

S

Sometwo

Limp Gawd
Joined
Nov 7, 2004
Messages
202
I have a Linksys router and attatched to it is a computer, and a small 5 port Linksys 10 Mbps hub. Attatched to the hub are a couple computers. When I try to transfer files from a computer connected to the hub to the computer connected to the router the collision light is solid red and it only goes at around 850kbps. I've also tried transfering files between 2 computers that are attatched to the hub and agian the collision light is solid red and the speed is slow. However, if I remove the hub and transfer files between 2 computers both attatched directly to my router, the speed is 9mbps. The network cables I am using are manufactured so I doubt that's the problem. What is going on and how can I fix this?
 
Hubs are prone to collision. Only way to eliminate the problem is to replace is with a switch.
 
10 Mbit is only a tad over 1 MB/sec, when you factor overhead and the collisions, 850k is pretty reasonable to expect from the hub. Since file transfers require two-way communication, packets are trying to go both ways at the same time with no flow control from the hub, so collisions are bound to occur. Not to mention the hub is a "dumb" device and it's sending incoming data to every node on the network without regard to it's destination.

100 Mbit switches are cheap and commonplace, it's your best solution.
 
I understand that hubs are prone to collisions, just not that many. The collision light is solid red, not just blinking every once in a while. I have to have a hub since it's the easiest way to sniff network traffic, so I'll I'll look into getting a faster hub then. Any suggestions on a cheap 100Mbps hub?
 
I just bought a Netgear 8 port gigabit switch with jumbo frame support for $55 at the egg. One of the nice metal ones!

I've seen the plastic Netgear 5 ports at Circuit City on rebate for $30.
 
This is an interesting problem.

Please correct me if I am wrong, but given my limited knowledge of ethernet, if you only have 2 computers connected to the hub, you should have just as many collisions as with a router. So why is the hub causing so many collisions? Also, shouldn't ethernet's csma/cd keep collisions to a minimum?
 
Sometwo said:
I understand that hubs are prone to collisions, just not that many. The collision light is solid red, not just blinking every once in a while. I have to have a hub since it's the easiest way to sniff network traffic, so I'll I'll look into getting a faster hub then. Any suggestions on a cheap 100Mbps hub?
Click to expand...

If your using it for sniffing then you should see if you can find a local retailer tht has a couple in stock. I bought a "hub" that wasent a hub and was useless for sniffing. Lucily I went back and bought one of the other "hub's" and it was actualy a hub.

You may want to consider a Cisco 2900 10/100 switch. It has the ability to do a port span then you get a switch with the ability to monitor traffic. About $100 on Ebay, plus you get a good introduction to Cisco.
 
moetop said:
If your using it for sniffing then you should see if you can find a local retailer tht has a couple in stock. I bought a "hub" that wasent a hub and was useless for sniffing. Lucily I went back and bought one of the other "hub's" and it was actualy a hub.

You may want to consider a Cisco 2900 10/100 switch. It has the ability to do a port span then you get a switch with the ability to monitor traffic. About $100 on Ebay, plus you get a good introduction to Cisco.
Click to expand...

Yeah I had that problem too, bought a hub that was actually a switch before I found this real hub I'm trying to use now. That's a really good idea on the Cisco switch, it's a cheaper than I thought it would be, but still a little too much so I'll think about it. Thanks for your help.
 
jimmyb said:
This is an interesting problem.

Please correct me if I am wrong, but given my limited knowledge of ethernet, if you only have 2 computers connected to the hub, you should have just as many collisions as with a router. So why is the hub causing so many collisions? Also, shouldn't ethernet's csma/cd keep collisions to a minimum?
Click to expand...

No, hubs are half duplex meaning they can only send or recieve one at a time, switches are full duplex meaning they can send and recieve data at the same time. So switches don't have collisions, where hubs do. I'm not sure why there are so many collisions with my hub, but CSMA/CD is just a means of detecting and recovering from collisions through a "truncated binary exponential backoff algorithm." (That's the first IT thing I ever read that made me say woah) so CSMA/CDetection, isn't really CSMA/CPrevention.
 
Thanks for the info.

For clarification:
I thought "csma" was the detection of an absence of a signal before transmission ("carrier sense"), and "cd" was the collision detection and immediate backoff.
 
Hubs are easily affected by collision storms and get real nasty until the things are disconnected and reconnected.
 
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