Dumb question on virtual pc network speeds

[SlickRCBD]

My newest computer has a gigabit Ethernet card, but I'm using an old
Linksys Fast Ethernet router/switch on my home network. This isn't
really a problem because ONLY the newest computer has a gigabit
Ethernet card, everything else but the oldest computer have 10/100
cards.
However, I have a question about using the virtual network with
virtual PC. If I send traffic from one virtual machine to another or
to the host machine, will I get gigabit Ethernet speeds or does it
actually go through the switch and is thus limited to fast Ethernet?

Obviously if I try to access another machine on the LAN or the
internet it goes through the switch, but what about virtual machine to
virtual machine?

[Andrew Morton]

Post by SlickRCBD
My newest computer has a gigabit Ethernet card, but I'm using an old
Linksys Fast Ethernet router/switch on my home network. This isn't
really a problem because ONLY the newest computer has a gigabit
Ethernet card, everything else but the oldest computer have 10/100
cards.
However, I have a question about using the virtual network with
virtual PC. If I send traffic from one virtual machine to another or
to the host machine, will I get gigabit Ethernet speeds or does it
actually go through the switch and is thus limited to fast Ethernet?
Obviously if I try to access another machine on the LAN or the
internet it goes through the switch, but what about virtual machine to
virtual machine?

If you check the hardware inside the virtual PC, does it happen to say it's
a 10/100 card?

What speeds did you get when you tested it?

[GG]

just in case someone wonders:
to speed up the the VPC network traffic among VMs, either bump up the speed
with a gigabit switch, or add an microsoft "virtual" adaptor knwon as loop
back adaptor. each Vm can use tow nic, one for internet, one for internal
files share on teh loop back...

Post by SlickRCBD
My newest computer has a gigabit Ethernet card, but I'm using an old
Linksys Fast Ethernet router/switch on my home network. This isn't
really a problem because ONLY the newest computer has a gigabit
Ethernet card, everything else but the oldest computer have 10/100
cards.
However, I have a question about using the virtual network with
virtual PC. If I send traffic from one virtual machine to another or
to the host machine, will I get gigabit Ethernet speeds or does it
actually go through the switch and is thus limited to fast Ethernet?
Obviously if I try to access another machine on the LAN or the
internet it goes through the switch, but what about virtual machine to
virtual machine?

[Dave Warren]

Post by GG
to speed up the the VPC network traffic among VMs, either bump up the speed
with a gigabit switch, or add an microsoft "virtual" adaptor knwon as loop
back adaptor. each Vm can use tow nic, one for internet, one for internal
files share on teh loop back...

huh?

VPC's internal virtual switch speed isn't related to the physical NIC
media speed in any fashion.

The only way the physical network makes a difference here is if the VM
environment is bound to a different NIC than the physical machine or if
the VMs live in different subnets (in which case the router's speed
comes into play here)

Traffic from one VM to another on the same host within the same subnet
doesn't even touch the physical NIC.

[GG]

Post by Dave Warren
Traffic from one VM to another on the same host within the same subnet
doesn't even touch the physical NIC.

I agree that it is possible that network traffic does not touch the
physical NIC like you said.

However traffic will have to go thru the NIC and router if the the VMS and
the host share a physical NIC and network thru a router.when there is no
shared network via the vm setting

try this:
-disconnect the cable from the NIC
-try access the host from VM or vice versa

[Dave Warren]

Post by GG

Post by Dave Warren
Traffic from one VM to another on the same host within the same subnet
doesn't even touch the physical NIC.

I agree that it is possible that network traffic does not touch the
physical NIC like you said.
However traffic will have to go thru the NIC and router if the the VMS and
the host share a physical NIC and network thru a router.when there is no
shared network via the vm setting

There's no settings here, but rather, the way the virtual network
implementation works is by creating a virtual switch within the host
machine, delivering packets between the guests, the host OS and the
physical NIC.

Post by GG
-disconnect the cable from the NIC
-try access the host from VM or vice versa

This is true, but only because the virtual NIC reports a disconnected
state, the IPs (in the host and guest) are dropped and the IP stack
refuses to accept or pass traffic, so traffic stops flowing.

If your physical NIC supports it, turn off physical media state
detection/reporting and try again, you should be able to deliver traffic
between your host and guest(s) in this state.

It's also worth noting that your network's physical router will likely
not route packets from one host to another in the same subnet, packets
within the same subnet are not routed and are simply delivered by the
hub or switch (and never back to the source port, since doing so would
immediately create a loop as soon as you had two switches in a single
LAN)

[GG]

thx for detailed explaination.

Post by Dave Warren
It's also worth noting that your network's physical router will likely
not route packets from one host to another in the same subnet, packets
within the same subnet are not routed and are simply delivered by the
hub or switch (and never back to the source port, since doing so would
immediately create a loop as soon as you had two switches in a single

however most router has some sort of switch included, if there is no
additonal switch, does not the builtin switch limit thruput?
why is the throughput between host and VM can only be at 3 MB/s when the
router is 100/10mbs when the NIC is the gigabit type? btw the wire between
the router and PC is only a 4 ft.

I have seen vm and host connected thru Gigabit NIC to Gigabit switch
achiieving thruput of about 200mbs which is the max thruput limited by the
long wire of the host to the rest of the network
LAN.

using null adaptor is entirely different would only be limited by the PC's
motherboard and CPU as well as other loads

[GG]

further on loopback adator

If the TCP/IP properties are configured to use DHCP, the adapter will
eventually use an autonet address (169.254.x.x/16) because the adapter is
not actually connected to any physical media.

Note By default, TCP/IP properties are configured to use DHCP.