Multiple WiFi adapters

A while back there was a discussion of how Windows chooses which
network connection to use when there is both a wired and wireless
connection:
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Does that same discussion apply to multiple wireless connections?
I.e., if my laptop's internal WiFi adapter and my USB-connected
WiFi adapter are both connected to the same NAP, is the "least
expensive" connection still used?
Does each connection automatically get a different Metric value?
Can those values be manually assigned?
Is there any down side to having both connections active?
Thanks.
Reply to
Dave Rudisill
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Yes
No. I tried this in Nov. on Vista.
Yes In the Advanced TCP/IP settings uncheck the "Automatic Metric" box and enter whatever figure you want in the "Interface Metric" box.
If you are running on battery then you are wasting power.
I do run both adapters on a linux machine but they tend to be doing different tasks and not connected to the same AP.
Reply to
LR
Yes. The major issue is that each "interface" (that's an ethernet port, wireless card, or other network connection) must have a unique MAC address associated with it. You can't have the same IP address assigned to multiple MAC addresses. Therefore, you can't have multiple connections with the same source IP address. If you simultaneously run multiple ethernet or wireless cards, the output of:
ipconfig /all | find "Address"
Physical Address. . . . . . . . . : 00-02-B3-1E-43-17 IP Address. . . . . . . . . . . . : 10.0.0.11 Physical Address. . . . . . . . . : 00-02-B3-1E-39-ED IP Address. . . . . . . . . . . . : 192.168.1.11
The two IP addresses are the result of having two ethernet adapters in my desktop.
If I connected to a remote VPN server, there would be a third IP. Might as well try... yep, it works:
ipconfig /all | find "Address" Physical Address. . . . . . . . . : 00-02-B3-1E-43-17 IP Address. . . . . . . . . . . . : 10.0.0.11 Physical Address. . . . . . . . . : 00-02-B3-1E-39-ED IP Address. . . . . . . . . . . . : 192.168.1.11 Physical Address. . . . . . . . . : 00-53-45-00-00-00 IP Address. . . . . . . . . . . . : 192.168.111.141
Anyway, if I try to assign the same IP address to any two of these interfaces, Windoze will complain. This may not seem relevent, but please read on.
Yes. The problem is the same as previously mentioned. Each interface on your laptop has to be unique. Different MAC and by implication, different IP. However, your IP route to the router will be different for each wireless card. You can connect, associate, login, and connect, but the traffic will only move through one of the wireless connections. Unless you're running some load balancing router software, that distributes the traffic from multiple IP's to a single destination IP (i.e. your router's IP address), it's going to be very unbalanced traffic. Worse, you can't switch destinations on the fly, because that will initiate a disconnect.
All is not lost. You can connect two seperate wireless cards to two seperate access points (each with a unique IP address) and simultaneously move traffic to both. That's done with a static route to one of the routers and the network behind it. The other route is the default route, which takes care of everything else.
You might want to read the research articles under:
It's not directly related to what you're doing, but the last two articles do expand on my previous ranting.
I dunno. The above example with 3 connections yielded a metric of 1 for all connections. There's actually a 3rd ethernet card installed that I forgot to enable. When I turned it on, it didn't get a DHCP assigned IP address and received a metric of 30. However, in all other respects, the other 3 interfaces have equal route "costs". Incidentally, this is on Windoze 2000 SP3. I'm too lazy to get my XP laptop out of the truck and see what it does. I suspect it's different, as Vista might be because I vaguely recall that there were some changes in various service packs.
Yes.
Configuring Multiple Adapters on the Same Physical Network
The bottom of the page shows how to manually tweak the route metric.
An explanation of the Automatic Metric feature for Internet Protocol routes
Self interference. Even if the two wireless adapters are on different 2.4GHz channels (which is impossible when connecting to a single access point), you're gong to have mutual interference. You might get away with connecting to two different access points, on different channels, or preferably, different bands.
Also, stuffing in a 2nd interface to the same destination does NOT double your thruput. You get whatever speed is supplied by the single wireless interface, with the other wireless interface doing nothing.
If you have any questions, BEFORE you ask, please supply: 1. What are you trying to accomplish? 2. What do you have to work with? 3. What have you done so far and what happened?
Reply to
Jeff Liebermann

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