On Thu, 09 Apr 2009 07:15:44 -0400 "Robert E. Seastrom" <rs@seastrom.com> wrote:
Seth Mattinen <sethm@rollernet.us> writes:
I have a few Sprint EVDO cards. They go into standby when nothing is actively going on and fire up within seconds when there is something to do. I regularly use everything from SSH to streaming video without any issues. I only notice the delay with SSH when I don't type anything for a few minutes and it has to come active again, but I can leave it idle for hours and it never drops.
Interesting. When I got my Sprint EVDO card (u727) a year and a half ago, they were pretty nasty about gunning down (bidirectional spoofed RST coming out of the middle of the network somewhere) any TCP sessions that were idle for ten minutes or more. Quite repeatable and verified on the downlow by People With Insight that this was in fact expected behavior from boxes that were in the middle of the network due to "politics" (unlike Verizon, Sprint appears to put no restrictions on inbound connections to the evdo-host). Putting this:
ServerAliveInterval 60
in ~/.ssh/config was an effective work-around. I have not revisited the issue to see if Sprint has corrected this behavior. Perhaps budget constraints or customer complaints have caused Sprint to revisit the necessity of having extraneous hardware in their network.
I use a Verizon Wireless u727; before that, I used a PCMCIA card. I've never had problems with drops on idle. *However* -- if there was a packet from the wrong IP address, the older card would drop the connection -- apparently, that behavior was required by the spec. (I haven't checked if the newer one will do that.) So, if the EVDO connection dropped while I had, say, an IMAP or ssh session open, and I dialed back in, the next TCP packet would cause EVDO to drop again... I finally "fixed" it by creating ipfilter rules in my ppp-up script to block all "bad" packets from going out. --Steve Bellovin, http://www.cs.columbia.edu/~smb