...
The main purpose of TULIP Central Reflector is to proxy the TULIP queries to landmarks in PlanetLab's Scriptroute Service. It may also be extended to issue all queries. This decision will be related to speed of execution and security among other things service, and the perfSONAR and PingER reverse ping servers. The PlanetLab Scriptroute service provides a cookie which works for a single IP address only. So in this way all the requests will be issued from the Central reflector and the responses will be sent back to the TULIP JNLP Client.
Implementation
Wiki Markup
Requirements
- Should fetch sites.txt or have a local copy of sites.txt, what changes should be made to sites.txt ?
- A new parameter should be added to sites.txt to include teir0 or tier1. Also the region of tier1 sites needs to be specified in sites.txt
- A separate thread should be used for each landmark and Semaphores should be used for locking, so that data from different threads should not inter-mix.
- There should be a limit on the number of threads that can be launched at a time (say 10).
- Should there be extra logging on the reflector or can we rely on the standard web logs which will log each query including time stamp, the client name. What else it logs depends on whether the request is Get or a Post.
- Where are the results parsed, could be in the reflector or in the Java client. In the client distributes the parsing load, reduces the load on the reflector, simplifies the CGI script.
- What should happen if a landmark responds with a bad data. ( Should it process the error or send the raw data back?). Since there will be some anomalies I suspect the reflector will need to return the full response and anyhow needs to inform the user, so I suspect initially the client will process the response and spot errors etc.) Also if the client parses the result it will probably be easily able to spot problems.
- Special consideration for security as the script ultimately has to be deployed at SLAC (Perl taint option, warning option, special open method etc)
- Need to agree on a common format for the exchange of data.
- Needs a blacklisting mechanism for malicious hosts.
...
| Code Block |
|---|
http://www-wanmon.slac.stanford.edu/cgi-wrap/reflector.cgi?region=North%20America&target=134.79.16104.980&tier=all&type=PlanetLab&ability=1 |
...
There are about 60 SLAC/Looking Glass landmarks, and about 156 PlanetLabs landmarks. We filter the landmarks nightly using tulip-tuning.pl to disable non- or poorly responding landmarks, and re-enable them when they are working well. The PlanetLab landmarks send 10 pings very quickly, whereas the SLAC/Looking Glass landmarks send five 56 byte pings with one second between them, they will also wait for a deadline time of 30 seconds for pings to be replied to.
...
| Code Block |
|---|
3 packets transmitted, 5 packets received, 1.67 times amplification |
...
PlanetLab
...
Landmarks
To access the PlanetLab landmarks one needs a cookie that is associated with a subnet (in our case 134.79/16). In addition one needs a ruby script that is sent to the PlanetLab landmark to execute. These are put together by reflector.cgi to create a URL in hex form.
Errors Reported by PlanetLab
Failed to connect to http://Wiki Markup
ERROR: you're (134.79.18.134) already running a measurement on socket 14. [http://128.83.122.179]
10 packets transmitted, 0 received, 100% packet loss, time 0 ms rtt min/avg/max = 0/0/0 [http://141.149.218.208]
Can't resolve DNS: submitted:6:in `ip_dst=': unable to resolve $target: running in a chroot without dns support (RuntimeError)
submitted:9: warning: didn't see packet 5 leave: pcap overloaded or server bound to incorrect interface?
To 134.79.16.9 timed out
Error connecting: Connection refused
ERROR: you need a valid scriptroute authentication cookie to use this server, or the cookie you used does not match\
your client IP 134.79.18.163; go to [http://www.scriptroute.org/cookies.html] to get one.
ERROR: you're (134.79.18.134) already running a measurement on socket 10.
PlanetLab Server Error: Received: IP (tos 0xc0, ttl 253, id 51592, offset 0, flags \ [none\], length: 56)
192.70.187.218 > 198.82.160.220: icmp 36: time exceeded in-transit
Error connecting: No buffer space available
submitted:9:in `send_train': scriptrouted error: unable to send to 137.138.137.177: No buffer space available (ScriptrouteError)
Parsing the SLAC Landmarks
...
Simultaneous landmarks | Parallel requests / landmark | Request timeout | Duration (secs) |
|---|---|---|---|
20 | 5 | 2 | 50 |
20 | 5 | 10 | 60 |
10 | 5 | 2 | 88 |
40 | 5 | 2 | 34 |
20 | 10 | 2 | 50 |
Performance Version=3.0
There was a problem found with reflector that the request timeout was fixed at 5sec and the parallel requests was fixed at 10. Modifying the parameters in the code didn't change anything. This was causing two problems, 1) 5 seconds was too less for most of the landmarks causing large number of timeouts and 2) The speed of the script was not fast enough. The timeout was changed to 10sec and the number of parallel requests was increased to 80. During the time of testing there were a total of 200 active landmarks of which 91 were in North America, 15 in South Asia and 49 in Europe.
Region | Tier | Time (seconds) |
|---|---|---|
All | 0 | 10 |
North America | 1 | 23 |
Europe | 1 | 35 |
South Asia | 1 | 17 |
All | All | 65 |
Testing
It can be tested from a web browser by entering the URL (e.g. from a browser or from wget), e.g.
...
We have also considered whether the knowledge that a machine and possibly the usual owner can be accurately located may violate some privacy issue. This may require us to add some fuzz to results. So far this has not been done.
Sample Scripts
traceroute.pl: This script has been written with special security considerations so it will help in implementing reflector.cgi
...