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TimothyMDean

Configuring subnet within extended airport network

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I recently switched to a municipal WiFi service to get rid of Comcast in my house. It works reasonably well for me, but because the wireless modem had to be placed upstairs rather than downstairs, I had to extend my network using multiple Airport and Airport Express base stations. Here is what I have:

 

- Wireless modem managed by ISP. Has NAT-assigned IP address, and I have no access to change how that is configured.

- Airport Express #1 in vicinity of modem, connected via ethernet. Creates local Wifi network in my house. Internet connection sharing configured to use bridge mode. IP address is presumably being assigned by wireless modem's DHCP. Router address is 192.168.30.1, presumably the local IP address assigned to the wireless modem.

- Airport Express #2 one floor down, wirelessly extending local WiFi network created by AE #1. IP address presumably being assigned by wireless modem. Router address is 192.168.30.1

- Time Capsule in basement, wireless extending local WiFi network created by AE#1 (and extended by AE #2). IP address presumably being assigned by wireless modem. Router address is 192.168.30.1

- Mac Pro in basement, wired via ethernet to TimeCapsule. IP address presumably being assigned by wireless modem. Router address is 192.168.30.1

- Apple TV in basement, wired via ethernet to TimeCapsule. IP address presumably being assigned by wireless modem. Router address is 192.168.30.1

- 2 iPads in use throughout the house at various times

 

 

This setup works for most purposes. I have access wherever I need it in the house using one extended WiFi network. I realize that the multiple extensions of a single network slow things down, but for most of the things I do I am OK with that. NetFlix streaming delays for a minute to buffer before starting, but once past that it runs smoothly. The only time I have a problem with that is when I want to stream content from the basement Mac Pro to the AppleTV sitting 5 feet away from it. It sometimes works, but often is so horribly slow that it is unusable. For example, It can sometimes take an hour or more for a program to start while it buffers the content enough to get going. My initial thought was that I had something wrong with my home sharing setup, but then I never had this problem before I changed ISPs and introduced this extended network.

 

My current theory is that the slowness is being caused by (a) the way I've extended the network multiple times and all the overhead that introduced, and (B) the fact that the streamed data probably needs to travel from the Mac Pro source, up multiple floors through multiple base stations, and then back down again to the Apple TV. Streaming from the internet "one-way" down through the house is usable, but once you throw in the up-and-down transmission it seems to break some threshold and becomes unusable. Does this theory make any sense, or is there a more logical explanation I'm missing?

 

Assuming my theory is correct, I am wondering about the best way to deal with the problem. I think what is needed is for the basement to be configured as its own subnet so that traffic between nodes in the basement (i.e. the MP and the ATV) can be kept local without having to travel upstairs via an extended wireless network. The path upstairs would still need to be configured for internet-access, but for basement-to-basement traffic it wouldn't be used. Does that make sense or am I looking at it the wrong way?

 

If I go this route, are there specific configurations I should be using? Do I need to manually assign IP addresses and subnet masks to do this or is there a straightforward way to configure this using Apple Airport Utility?

 

Thanks for any advice,

 

-Tim

Edited by TimothyMDean

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Thanks John, but I don't think that's my issue. I'm not trying to download anything through iTunes or via any other internet location. I am trying to stream video directly from my Mac Pro to an Apple TV sitting 5 feet away from it. My suspicion is that my network config causes the streamed data to travel wirelessly (and unnecessarily) throughout the whole house and back again. My network downloads via iTunes and NetFlix streaming have been acceptable (although not as fast as when I was using Comcast cable internet)

 

I've got a tech support request into my ISP to see if they have any advise on setting up subnets within my house, but I'm not expecting much.

 

-Tim

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the wireless network is likely dropping speed to deal with the distance or interference. even if you force wireless N. or wireless G. it will scale down to deal with errors.

 

use a tool like iStumbler to do a site survey. if there are any other close by wireless networks on the same channel as yours this can cause slowness on your network. switch to a different channel. your best choices are 1, 6, and 11. although there are other channels there are worthless because they overlap.

 

other devices might interfere as well: baby monitors, microwave ovens, wireless cameras.

 

it's possible that the router itself is bad. it could also be a faulty cable connecting the router to your network.

 

you are possibly using the word subnets incorrectly. look it up. all of your devices should be on the same "subnet" as defined by your IP address supplied by DHCP from your router. the question that isn't answered above is what are the IP addresses of all your devices. this will determine if you have the "dreaded double NAT" problem. this is when you plug your Airport to your network using the WAN connector instead of the LAN side. setups like this cause your data to go through TWO routers and cause all kinds of problems with screen sharing, skype and other per-to-per tools.

 

so log into those airports, macs and other devices and make an IP address list.

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the wireless network is likely dropping speed to deal with the distance or interference. even if you force wireless N. or wireless G. it will scale down to deal with errors.

 

use a tool like iStumbler to do a site survey. if there are any other close by wireless networks on the same channel as yours this can cause slowness on your network. switch to a different channel. your best choices are 1, 6, and 11. although there are other channels there are worthless because they overlap.

 

other devices might interfere as well: baby monitors, microwave ovens, wireless cameras.

 

it's possible that the router itself is bad. it could also be a faulty cable connecting the router to your network.

 

you are possibly using the word subnets incorrectly. look it up. all of your devices should be on the same "subnet" as defined by your IP address supplied by DHCP from your router. the question that isn't answered above is what are the IP addresses of all your devices. this will determine if you have the "dreaded double NAT" problem. this is when you plug your Airport to your network using the WAN connector instead of the LAN side. setups like this cause your data to go through TWO routers and cause all kinds of problems with screen sharing, skype and other per-to-per tools.

 

so log into those airports, macs and other devices and make an IP address list.

 

I've checked all the IP addresses and confirmed they are all on the same network right now. IP addresses are all 192.168.30.X, with subnet mask of 255.255.255.0. Wireless router from ISP is 192.168.30.1

 

I've done the iStumbler survey and I don't have channel overlap issues. I'm on channel 1 using an 802.11n-only network. Only other networks in the area are on 11. I've also tried switching to the 5GHz frequency range to avoid interference from any devices in the 2.4 GHz range, and see no differences (I've since switched back to 2.4GHz because I get slightly better signal range with it)

 

Bad router or cable connections don't make much sense because traffic going only one direction (Internet, through upstairs wireless routers, down to basement) works just fine. Only when I have bi-directional packet transmission (basement computer, up 2 floors to wireless router, back down 2 floors to basement TV) do the problems come up.

 

What I want to do is make sure that packets going from one wired basement device to another wired basement device don't need to be transmitted and re-transmitted wirelessly up 2 floors and back down again to get to their destination. I'd like the ability for the basement router to realize that it is wired directly to the destination device and send packets to it directly, rather than transmitting wireless packets unnecessarily. One way to do this would be to just set up my basement router to assign its own IP addresses and then access the internet by a DHCP assignment from the upstairs wireless router. However, I think that would result in double-NAT issues.

 

The subnet approach I was considering was something like this:

  • Change the subnet mask from 255.255.255.128
  • Define the upstairs devices (network 0) with IP addresses between 192.168.30.2 - 192.168.30.127
  • Define the basement devices (network 1) with IP addresses between 192.168.30.128 - 192.168.30.255
  • Set up the basement routers default gateway as 192.168.30.1, so that packets destined for upstairs nodes would be routed there

 

I think this (or something like it) would work in theory, but I'm not sure if it can be done with the way my ISP assigns IP addresses. I also don't know if it would create double-NAT problems when I introduce these manually assigned IP addresses.

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I just realized that one other detail might not be obvious in my description above: In order to avoid Double-NAT problems in the Airport Express that creates my wireless network, I have to set it up in bridge mode. When the other base stations extend that network, they also must be in bridge mode. Based on my limited understanding of bridge mode, I think that means that none of the router actually do any IP routing. They just pass packets directly to the wireless router upstairs. That is why I believe that I need a separate network or a subnet of my main network: I need to make sure that the basement router can route traffic from basement device to basement device.

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don't over think networking. there is no reason to try to separate out your network by location. if all your devices are DHCP'd by one device (your main router) they should talk per-to-per without intervention. 

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So you're saying there's no reason to try and have my streaming content stay on the wired portion of the network rather than unnecessarily flying through the house wirelessly? There's no possibility that the need to transmit/receive wireless packets through 3 wireless routers in each direction is the reason why my performance is unacceptable when streaming from one basement computer to a basement AppleTV?

 

Is there another explanation that fits the symptoms?

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the route doesn't go "through" a router. to prove that the command line traceroute will tell you if you are hitting more than one router. for example here's the route to my color printer:

 

john:~ john$ traceroute 192.168.1.177
traceroute to 192.168.1.177 (192.168.1.177), 64 hops max, 40 byte packets
1  192.168.1.177 (192.168.1.177)  2.827 ms  1.483 ms  1.259 ms

 

1 hop to get there. yep. it's a wired connection. so here's the same thing using the Airport.

 

john:~ john$ traceroute 192.168.1.177
traceroute to 192.168.1.177 (192.168.1.177), 64 hops max, 40 byte packets
1  192.168.1.177 (192.168.1.177)  2.857 ms  2.070 ms  2.050 ms

 

still one hop. but note the slower PING times. which was expected.

Edited by johnfoster

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the route doesn't go "through" a router. to prove that the command line traceroute will tell you if you are hitting more than one router. for example here's the route to my color printer:

 

john:~ john$ traceroute 192.168.1.177
traceroute to 192.168.1.177 (192.168.1.177), 64 hops max, 40 byte packets
1  192.168.1.177 (192.168.1.177)  2.827 ms  1.483 ms  1.259 ms

 

1 hop to get there. yep. it's a wired connection. so here's the same thing using the Airport.

 

john:~ john$ traceroute 192.168.1.177
traceroute to 192.168.1.177 (192.168.1.177), 64 hops max, 40 byte packets
1  192.168.1.177 (192.168.1.177)  2.857 ms  2.070 ms  2.050 ms

 

still one hop. but note the slower PING times. which was expected.

 

Normally I would agree with you. However, when in bridge mode my understanding is that a router simply passes packets through at the link level, and that the IP-level tools like traceroute that use ICMP messages would never be aware of any bridges it is going through. A quick google search led me to this FAQ which suggests the same:

 

Q: The bridge appears to work, but why doesn't traceroute show the bridge as a part of the path?

A: Due to the nature of a bridge, a traceroute should NOT show the bridge as a part of the path. A bridge is to be a transparent component of the network.

 

Of course it is possible that Apple base stations configured in bridge mode are not truly acting in this way, but I've seen numerous posts on the web suggesting that it does. As a result, I wouldn't expect traceroute to show my intermediate base stations even if packets have to be transmitted through those base stations.

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