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Subject2.2.17 IP masq bug
While setting up a cluster, and I've stumbled across what appears to be a bug
in the IP masqing of 2.2.17.

Here's my setup:
15 machines on 10.0.0.1-15. 10.0.0.1 has IP aliasing and is also on the
external net, so it can IP masq the other 14 machines. The machines are on a
switch, and share a semi-switched network segment with a bunch of other
external IP'd machines (we are all in the same lab, actually).

The bug:
When I make a connection from any internal node to the one of the other
externally routed machines in my lab, then close it, this external machine then
becomes unreachable to successive connects from that node.

ex:
[root@node2 /root]# telnet 128.174.21.2 22
Trying 128.174.21.2...
Connected to fake.ip.uiuc.edu (128.174.21.2).
Escape character is '^]'.
SSH-1.5-1.2.27
^]
telnet> q
Connection closed.

[root@node2 /root]# telnet 128.174.21.2 22
Trying 128.174.21.2...

...

The problem also happens if I telnet to a closed port a few times in a row.
Soon the machine is unreachable by any network traffic from that node. If I
switch to a new node, I can connect just once from that node, and then
silence.

This problem does NOT manifest itself for connecting to machines outside of
the local network. That seems to work fine.

More detailed setup info:
If it matters, all internal machines use eepro100's, and netboot via
dhcp/PXE off of the 10.0.0.1 machine.

Here's a sample routing table of the internal machines:
[root@node2 /root]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
10.0.0.0 0.0.0.0 255.0.0.0 U 0 0 0 eth0
127.0.0.0 0.0.0.0 255.0.0.0 U 0 0 0 lo
0.0.0.0 10.0.0.1 0.0.0.0 UG 0 0 0 eth0

And the world node:
[root@world /root]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
128.174.21.50 0.0.0.0 255.255.255.255 UH 0 0 0 eth0
128.174.21.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
10.0.0.0 0.0.0.0 255.0.0.0 U 0 0 0 eth0
127.0.0.0 0.0.0.0 255.0.0.0 U 0 0 0 lo
0.0.0.0 128.174.21.11 0.0.0.0 UG 0 0 0 eth0

And the script to load the IP masq modules and setup ipchains:
#!/bin/sh
/sbin/ifconfig eth0:0 10.0.0.1
echo 1 > /proc/sys/net/ipv4/ip_forward
/sbin/ipchains -F input
/sbin/ipchains -F output
/sbin/ipchains -F forward
/sbin/ipchains -P input ACCEPT
/sbin/ipchains -P output ACCEPT
/sbin/ipchains -P forward DENY
/sbin/ipchains -A forward -s 10.0.0.0/8 -j MASQ

All the ip masq modules are loadded:
[root@world /root]# lsmod
Module Size Used by
ip_masq_vdolive 1336 0 (unused)
ip_masq_user 2632 0 (unused)
ip_masq_raudio 3000 0 (unused)
ip_masq_quake 1352 0 (unused)
ip_masq_portfw 2560 0 (unused)
ip_masq_mfw 3144 0 (unused)
ip_masq_irc 1592 0 (unused)
ip_masq_ftp 2616 0 (unused)
ip_masq_cuseeme 1080 0 (unused)
ip_masq_autofw 2480 0 (unused)

The problem still occurs with no modules loaded.

--
Mike Perry
http://so.fscked.org
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