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jchao3

2 Posts

4442

July 8th, 2005 15:00

PowerConnect 2708 and Machines on Different Subnets

Hello,
 
I have two machines running Windows 2000 connected to the same PowerConnect 2708 switch.
 
The two machines have the following network configurations:
 
Machine A:
 
IP Address: 111.112.113.114
Subnet mask: 255.255.0.0
 
Machine B:
 
IP Address: 111.112.115.116
Subnet mask: 255.255.255.0
 
I tried copying the exact same file between the two machines and observed the following:
 
When copying from machine A to machine B, the speed was very fast. However, when copying from machine B to machine A, the speed was significantly slower.
 
Can anyone explain why this happens? (If the PowerConnect 2708 is a Layer 2 switch and hence uses MAC addresses, shouldn't the copy speed be the same in both directions?)
 
Thanks,
 
Jerry
 

DELL-Randy

132 Posts

July 8th, 2005 18:00

Is one system a 10/100Mbps and the other a 10/100/1000Mbps or are the NICs in both systems the same speed / duplex?

jchao3

2 Posts

July 8th, 2005 19:00

Randy,
 
Both systems are 1000 Mbps. Do you think this has anything to do with the two systems being on different subnets from the point of view of machine B? I read somewhere that if the sender finds the receiver to be on a different subnet, then the sender's packets are first sent to a default external IP router. This is the case for B to A, but not for A to B due to the different subnet masks. The copying is therefore slower for B to A because the data has to travel much longer distances. I think layer 3 switches would solve this problem, but is there a solution that uses layer 2 switches like the PowerConnect 2708?
 
Thanks,
 
Jerry
 

DELL-Randy

132 Posts

July 11th, 2005 13:00

Essentially, due to subnetting, you are correct in that the system with the /24 mask will need to forward packets destined to a /16 address to a device capable of routing.  If this routing device is 10/100Mbps, then this will be a result of the degradated performance.  There should be minimal delay if the routing device is 1000Mbps -- such that it should not be noticeable in regards to performance.  A Layer 3 gigabit switch could potentially increase performance, again, if the current routing device is 10/100Mbps. 

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