Wireless
Motivation
The UW wireless network has a couple of major deficiencies:
- Weak signal in MC 3036, preventing some laptops from connecting
- Aggressive throttling of bandwidth, even to wired systems within the club office
- Ignorance of the "Don't Count" list
The second point is quite important: UW's wireless will begin to throttle high bandwidth connections after a minute or two, decreasing bandwidth slowly from 1MB/s or more down to 40KB/s or less. Members can expect to sit in the office for an hour or more if they want to download many packages off of the CSC mirror.
To work around this problem we have an access point in the Computer Science Club.
Configuration
- ESSID: csc-wireless
- AP: 00:19:5B:7D:DB:FE
- Channel: 36 (5.18 GHz)
- Network: auth3net (129.96.192.0/23)
Clients must authenticate to the Network Authentication Appliance (NAA) as with uw-wireless, in accordance with this IST policy, points #2 through #4.
Technical Overview
The AP connects to acesulfame-potassium through a secondary NIC. On acesulfame-potassium, the following decision is made:
- IP packets destined for mathstudentorgsnet are brouted with SNAT to wireless-nat.csclub.uwaterloo.ca
- All other ethernet frames are bridged to auth3net
The network is identical to connection through uw-wireless in all respects, except for the special treatment of mathstudentorgs traffic. This special treatment bypasses uw-wireless throttling for machines on our network.
Wireless Performance
Tests were done on a 700MB Ubuntu ISO at an off peak time.
- uw-wireless
- Initial speed: 1.3MB/s
- Final speed: 40KB/s
- Time: aborted after 27 minutes (got bored) with 67% remaining, ETA increased steadily throughout
mike@freyr:/tmp$ time wget http://mirror.csclub.uwaterloo.ca/ubuntu-releases/7.10/ubuntu-7.10-desktop-i386.iso --23:54:09-- http://mirror.csclub.uwaterloo.ca/ubuntu-releases/7.10/ubuntu-7.10-desktop-i386.iso Resolving mirror.csclub.uwaterloo.ca... 129.97.134.71 Connecting to mirror.csclub.uwaterloo.ca|129.97.134.71|:80... connected. HTTP request sent, awaiting response... 302 Found Location: http://citric-acid.csclub.uwaterloo.ca/iso/ubuntu-gutsy/ubuntu-7.10-desktop-i386.iso [following] --23:54:09-- http://citric-acid.csclub.uwaterloo.ca/iso/ubuntu-gutsy/ubuntu-7.10-desktop-i386.iso Resolving citric-acid.csclub.uwaterloo.ca... 129.97.134.37 Connecting to citric-acid.csclub.uwaterloo.ca|129.97.134.37|:80... connected. HTTP request sent, awaiting response... 200 OK Length: 729608192 (696M) [application/x-iso9660-image] Saving to: `ubuntu-7.10-desktop-i386.iso' 11% [===> ] 86,583,824 377K/s eta 13m 34ss 33% [========================> ] 241,791,104 39.5K/s eta 55m 48s real 27m40.165s user 0m1.008s sys 0m4.252s
- csc-wireless
- Initial speed: 2.12MB/s
- Final speed: 2.43MB/s
- Time: finished in 3m 31s
mike@freyr:/tmp/test$ wget http://mirror.csclub.uwaterloo.ca/ubuntu-releases/hardy/ubuntu-8.04-beta-server-i386.iso --2008-04-17 05:34:44-- http://mirror.csclub.uwaterloo.ca/ubuntu-releases/hardy/ubuntu-8.04-beta-server-i386.iso Resolving mirror.csclub.uwaterloo.ca... 129.97.134.71 Connecting to mirror.csclub.uwaterloo.ca|129.97.134.71|:80... connected. HTTP request sent, awaiting response... 302 Found Location: http://taurine.csclub.uwaterloo.ca/iso/ubuntu-8.04-beta-server-i386.iso [following] --2008-04-17 05:34:44-- http://taurine.csclub.uwaterloo.ca/iso/ubuntu-8.04-beta-server-i386.iso Resolving taurine.csclub.uwaterloo.ca... 129.97.134.34 Connecting to taurine.csclub.uwaterloo.ca|129.97.134.34|:80... connected. HTTP request sent, awaiting response... 200 OK Length: 526323712 (502M) [application/x-iso9660-image] Saving to: `ubuntu-8.04-beta-server-i386.iso' 2% [ ] 10,988,599 2.12M/s eta 4m 36s 4% [> ] 21,247,679 2.43M/s eta 3m 58s 6% [=> ] 31,897,719 2.41M/s eta 3m 41s 16% [=====> ] 85,867,575 2.40M/s eta 3m 2s 27% [=========> ] 143,900,519 2.36M/s eta 2m 38s 38% [==============> ] 203,245,351 2.36M/s eta 2m 11s 43% [================> ] 228,489,783 2.43M/s eta 2m 2s 51% [===================> ] 269,462,391 2.41M/s eta 1m 45s 58% [======================> ] 309,395,335 2.48M/s eta 88s 67% [=========================> ] 354,638,095 2.41M/s eta 70s 78% [==============================> ] 410,898,984 2.41M/s eta 47s 84% [================================> ] 444,207,328 2.42M/s eta 33s 94% [====================================> ] 498,937,384 2.39M/s eta 12s 97% [======================================> ] 514,212,336 2.39M/s eta 5s 99% [======================================> ] 524,255,664 2.43M/s eta 1s 100%[=======================================>] 526,323,712 2.43M/s in 3m 31s 2008-04-17 05:38:15 (2.38 MB/s) - `ubuntu-8.04-beta-server-i386.iso' saved [526323712/526323712]
These tests are sloppily done, to be sure, but still demonstrate the huge performance advantage of csc-wireless. I will repeat them without aborting, when I have time.
Detailed Configuration
Required Packages
To install required packages, type:
sudo aptitude install madwifi-source madwifi-tools wireless-tools vlan bridge-utils ebtables iptables iproute
Then build the modules for the installed kernel via:
sudo m-a a-i madwifi
Wireless Interface Configuration
First, configure the wireless interface. Use the following snippet:
auto ath0
iface ath0 inet manual
pre-up wlanconfig ath0 destroy || true
pre-up wlanconfig ath0 create wlandev wifi0 wlanmode ap
post-down wlanconfig ath0 destroy
wireless-mode master
wireless-channel 36
wireless-essid csc-wireless
Second, make a bridge between the wireless and auth3net. Use the following snippet, replacing IFACE by the interface connected to auth3net
auto br192
iface br192 inet manual
bridge_ports IFACE ath0
bridge_stp yes
up brctl setbridgeprio br192 40000
up ip route add 129.97.192.0/23 dev br192
Brouting Configuration
Additional setup is needed to enable fast communication between mathstudentorgsnet and auth3net. We take the minimally invasive approach of pulling packets destined for mathstudentorgsnet off the bridge and routing them, masquerading as wireless-nat.csclub.uwaterloo.ca. Masquerading is needed to ensure responses are routed correctly.
First, load the Atheros and 802.11q modules:
modprobe ath_pci 8021q
These need to be loaded early in the boot, so add them to /etc/modules:
ath_pci 8021q
Second, add 129.97.134.85 as a secondary IP address. You might do so by adding this snippet, replacing IFACE by the interface connected to mathstudentorgsnet:
auto IFACE:nat
iface IFACE:nat inet static
address 129.97.134.85
netmask 255.255.255.0
network 129.97.134.0
Next, enable routing, by typing the following:
echo 1 >> /proc/sys/net/ipv4/ip_forward
To make this permanent, add the following snippet to sysctl.conf:
net.ipv4.ip_forward=1
Third, configure ebtables to pull packets off the bridge. Type:
ebtables -t broute --flush
ebtables -t broute -A BROUTING -i ath0 \
-p ipv4 --ip-src 129.97.192.0/23 --ip-dst 129.97.134.0/24 \
-j redirect --redirect-target DROP
invoke-rc.d ebtables save
Finally, configure iptables to masquerade wireless users as wireless-nat.csclub. Type the following, replacing IFACE by the interface connected to mathstudentorgsnet:
iptables -t nat --flush
iptables -t nat -A POSTROUTING -o IFACE \
-s 129.97.192.0/23 -d 129.97.134.0/24 \
-j SNAT --to-source 129.97.134.85
invoke-rc.d iptables save
Ensure the appropriate routing table entry for auth3net exists--masquerading will not work without it. It is included in the bridge configuration snippet above.