red hat firewall question
Steve Phillips
steve at focb.co.nz
Wed Dec 5 00:38:38 UTC 2007
Anne Moore wrote:
> Hi Marshall
>
> Well I've already determined that this will fix the issues. The problem is
> indeed with our firewall and it cannot be changed due to our security
> policy. Thus, I created a script that continually pings every 30 seconds and
> that keeps the logons alive.
This is part of the problem with 'sekuritee people' that don't actually
understand the protocols.
TCP Keepalives are supposed to work to allow servers to figure out that
persistent connections that have not sent data are still there - the RFC
states that this should not default to anything less than 2 hours (its
possible, but not advised)
http://www.uic.rsu.ru/doc/inet/tcp_stevens/tcp_keep.htm for a good, easy
to read writeup
http://www.faqs.org/rfcs/rfc1122.html is the host requirements RFC,
section 4.2.3.6 deals with keep alives.
There are a number of reasons for this default (explained nicely in the
first link) and most sekuritee people cause no end of headaches for
systems/network people when they start fiddling with this value in the
name of 'sekuritee !'
It is completely normal for a TCP session to be idle, and it is also
completely normal for it to wake up hours later and send data, this is
simply how stuff works in the IP world, and what it appears is happening
is that your ssh sessions are (as would be expected) idle for a few
minutes and due to some sekuritee 'professional' deciding that this
could NEVER happen, your user sessions are being disconnected. The
correct fix is to lart the sekuritee moron and change the default keep
alive value. If they want to enforce logoff on idle sessions then
install or enable this on the servers. Changing these values on a
firewall can have some VERY undesirable and difficult to fault-find
consequences. (I had one instance where someone had set the value to 30
mins, oracle was timing out connections and things would sporadically
work, not work, then semi work - took the best part of a day to fault find.)
The primary purpose of keep alives is to enable the host to not exhaust
its resources by having 65500 dead yet open telnet/ssh/tcp sessions and
being able to close these after a defined period., the firewall not
working in sync with the host just compounds this problem, and depending
on the number of users/types of processes, can actually cause the
problem that keep alives are supposed to prevent.
--
Steve
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