odd things you discover late at night working on SOSP...

Stefan Savage (savage@cs.washington.edu)
Wed, 19 May 1999 19:38:42 -0700

Neal: I think there's a bug with the load detection algorithm in either
sting or ping

Stefan: Why?

Neal: sting seems to be reporting results 10 times higher than ping

Stefan: That's weird, let me look..... (pause) They're the same on
yahoo...

Neal: try xoom.com

Stefan: How strange, they are different... I wonder why that is....

To cut a long story short it turns out the there is a frobulator (firewall,
lb, shaper, etc...) that answers icmp echo request packets on behalf of
xoom.com. It has its own value of ip_id. I also has its own ttl base.
This suggests that we could use the sting/ping combination to detect web
sites behind firewalls.

- Stefan