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xen-users
Re: [Xen-users] antispoof with Xen 3
Dirk H. Schulz wrote:
Hi Mike,
Mike Wright schrieb:
Dirk H. Schulz wrote:
Hi folks,
I am trying to get antispoofing running on xen3 (based on Debian
Sarge). This is what I have done to enable it:
1. I have compiled a dom0 kernel with
CONFIG_NETFILTER_XT_MATCH_PHYSDEV=m
2. I made sure this module is loaded: lsmod gives xt_physdev (among
others).
3a. I have changed the line "(network-script network-bridge)" to
"(network-script network-bridge antispoof=yes)" in
/etc/xen/xend-config.sxp.
3b. I have also tried setting the default in network-bridge to yes by
changing the antispoof line to "antispoof:${antispoof:-yes}".
Then I have setup a domU with vif=['mac=ae:00:00:78:be:04,
ip=192.168.115.156'], but "inside" I have configured the ip address
of eth0 to be 192.168.115.157.
After starting the domU "ifconfig eth0" shows the ip address
192.168.115.157, but the domU still has network access to the outside.
That means: antispoofing does not work.
Hi Dirk,
I'll bet your iptables FORWARD default policy is ACCEPT. All
antispoofing does is specifically add a rule allowing that particular
source IP. Having a default policy of ACCEPT means that after failing
the source IP matching rule it gets accepted by the default policy.
Try adding this rule to iptables and see if it changes what you see.
"iptables -P FORWARD DROP"
Now only specifically allowed source IPs will pass.
Thanks for your help. You have had the right idea, but there is still a
problem. That is what I did:
Changed FORWARD policy to drop as you supposed. Checked with iptables -L
FORWARD that policy is DROP.
Tried pinging the outside from the misconfigured domU (misconfigured =
other IP in /etc/network/interfaces than in domU config file) - no
traffic to the outside possible. Good.
Changed IP in domU's /etc/network/interfaces to the one used in the domU
config file. Restarted domU. Pinged to an external machine - nothing.
Even with correct config no network connection!
Checking the FORWARD chain I have
- a policy of DROP
- an accept rule for all protocols from domUs IP address to anywhere
- an accept rule for udp from anywhere to anywhere
Do you have a dom0 rule allowing ICMP traffic?
Also, it is a good idea to turn off iptables in your domUs until after
basic networking is functioning well.
Both rules appear only after the start of the domU. So the configuration
should be okay, but there is no network connection from domU to dom0 or
to external machines.
This is where tcpdump comes in handy. You will have to inspect your
network traffic to see what is appearing where.
You might start on dom0 with "tcpdump -n port icmp" then ping a domU.
Look at the tcpdump output while pinging. You should see icmp traffic
leaving your dom0. Now run the same tcpdump command on the domU. Do
you see traffic coming in? Do you see a reply going out? That is a
good place to start. Adding -v to the tcpdump command will produce more
output.
:m)
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