On 15/07/10 10:34, John Haxby wrote:
Hello All,
For some time now, I've been using REDIRECT (roughly) like this:
$IPT -t nat -A PREROUTING -j proxyt
$IPT -t nat -A proxyt -d <network> -p tcp -m tcp -k RETURN
(repeated lots of times for different networks)
$IPT -t nat -A proxyt -p tcp -m tcp ! --dport 3128 -j REDIRECT
--to-ports 3128
That works just fine: TCP connections to any network other than the
specific get directed to the process listening on port 3128 (which
then uses HTTP CONNECT on a proxy to connect to the Big Bad Internet).
I use ebtables on a pair of machines running Xen to redirect traffic
to this machine:
+-------------+ +-------------+
| xen | | xen |
| +---+ | | +---+ |
| +---+ | P |=========| P'| +---+ |
| | A | +-+-+ | | +---+ | B | |
| +---+ | | | +---+ |
| | | | |
+---------|---+ +-------------+
|
Big Bad Internet
Traffic from A is redirected (by ebtables) to P which has these rules
on it and that connection is just fine. Traffic from B is directed to
P' which then forwards traffic to P over a private network and until
recently that worked just fine.
Previously, P was running Fedora 11 with the 2.6.30.10-105.2.16.fc11
kernel; but now its running Fedora13 with the 2.6.33.6-147.fc13.
So, previously on B I could connect to (say) google.com:80 and traffic
was redirect to the process listing on port 3128 via P' and the
private link and everything was fine.
Now, unfortunately, the same connection from B is hits the REDIRECT
rule but the process listening on port 3128 doesn't come out of the
accept(2) syscall. The same connection from A does work. The only
visible difference is that traffic from A appears to come into P from
eth0 and traffic from B appears to come from eth1. Inserting a LOG
target immediately before the REDIRECT rule shows the packet hitting
that REDIRECT (and one immediately after doesn't show anything so the
REDIRECT is definitely matching).
Something seems to have changed between 2.6.30 and 2.6.33 and I'm at a
loss to know what. I've looked around a bit, but so far haven't found
anything.
Hopefully someone listening will be able to say "oh, you need to do
<some magic>" :-) Or that this should never have worked in the first
place because of something horrible I was relying on.
In case anyone else comes looking this way, the problem commit was this one:
commit c1cf8422f0512c2b14f0d66bce34abb0645c888a
Author: Stephen Hemminger <shemminger@xxxxxxxxxx>
Date: Fri Feb 20 08:25:36 2009 +0000
ip: add loose reverse path filtering
Extend existing reverse path filter option to allow strict or loose
filtering. (See http://en.wikipedia.org/wiki/Reverse_path_filtering).
For compatibility with existing usage, the value 1 is chosen for
strict mode
and 2 for loose mode.
Signed-off-by: Stephen Hemminger <shemminger@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
The routing issue that I was having was that packets coming in on the
private link, having been redirected by ebtables on the second machine,
would be routed out on the normal connection (not shown in the diagram)
and so they we're being dropped before the REDIRECT rule even saw them.
The required magic was to set net.ipv4.conf.default.rp_filter=2
I suspect that this is going to bite quite a few people upgrading from
RHEL5 to RHEL6 who have previously been relying on loose reverse path
filtering with their asymmetric routing.
jch
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