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now with IPv6

In anticipation of World IPv6 Launch Day (6 June 2012), this website is now fully reachable over IPv6.
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IPv6 test websites

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Enabling IPv6 Privacy Extensions on all interfaces (Ubuntu Linux, may work for other distros too)

According to the Wikipedia IPv6 article, Privacy extensions are, except for the Windows platform and Mac OS X since 10.7 as well as iOS since version 4.3, not enabled by default.

In theory, one can enable the IPv6 Privacy Extensions on all interfaces at once using sysctl like this:
sudo sysctl net.ipv6.conf.all.use_tempaddr=2

However, this currently doesn't work as expected, so I'm using this one-liner in /etc/rc.local:
for IF in `/bin/ls /proc/sys/net/ipv6/conf/*/use_tempaddr` ; do echo 2 > $IF ; done

This also sets "use_tempaddr" for "default", which means it should also apply to interfaces added to the system afterwards.

A simple check to verify that the new configuration is working: ipv6-test.com will print your MAC address when available...

See also: Linux Kernel Bug 11655

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gulp - tcpdump alternative for lossless capture on Linux

tcpdump and wireshark are the tools that usually come to mind when you have to capture network traffic. But in some situations where you have to record a large amount of data and you want to avoid losing packets, tcpdump has some limitations. When I was hit myself by the tcpdump packet loss problem, I quickly found out that I was not alone and that a number of people had already researched the topic and/or provided alternatives.*

In particular, I found two different tools to perform the task: Corey Satten's gulp (http://corey.elsewhere.org/gulp/) and lindump from HP Labs (http://tesla.hpl.hp.com/opensource/)

I also found two interesting papers about capturing high volumes of traffic: http://www.usenix.org/events/fast09/tech/full_papers/anderson/anderson_html/ and http://docs.di.fc.ul.pt/jspui/bitstream/10455/3299/1/thesis-nhenriqu.pdf (the second quotes the first one among others, and also contains useful info to optimally spread the load among different cores)

After some tests I quickly became a happy gulp user, and thanks to the software being open source I was able to add features to it that I missed from the latest tcpdump versions:

-n - allows to change the default filename template
-t - allows to add a timestamp to the filename
-G - rotate pcap file every n seconds
-F - allows to skip the check for an ethernet interface
-Z - allows to specify a command to post-process each capture file

I've sent a patch to Corey Satten, who intends to setup a repository to hold the various contributions he gets for gulp. In the meanwhile, you can find my changes in the attached file (02-gulp-ntGFZ.patch.gz). For your convenience and for completeness, I also provide here the patch from Guy Harris that fixes issues on 64 bit systems (see http://seclists.org/wireshark/2009/Oct/105, apply that one first).

Updates:
2012-08-22: new version of my patch to fix the issue reported by SgtMalicious
2017-02-03: long-standing bug fixed

Downloads:
01-gulp-amd64.patch.gz: fix issues with 64-bit systems
02-gulp-ntGFZ.patch.gz: additional functionality as described above
gulp-1.58-crox.tgz: source with both patches applied

* other people have reported a performance drop with libpcap version 1.0 compared to previous builds, see http://thread.gmane.org/gmane.network.tcpdump.devel/4629 or http://seclists.org/tcpdump/2010/q3/index.html#11
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hping - [send_icmp] Unsupported icmp type

When performing tests you may sometimes want to send specially crafted icmp packets. hping is a handy tool for that.

However, the default behavior is to refuse to send "unsupported" Type/Code combinations. eg
hping3 -c 1 --icmp -C 33 -K 0 192.168.70.1
HPING 192.168.70.1 (wlan0 192.168.70.10): icmp mode set, 28 headers + 0 data bytes
[send_icmp] Unsupported icmp type!

Fortunately, there is an (undocumented) --force-icmp option that you can add to bypass the check:
hping3 -c 1 --icmp --force-icmp -C 33 -K 0 192.168.70.1
HPING 192.168.70.1 (wlan0 192.168.70.10): icmp mode set, 28 headers + 0 data bytes

--- 192.168.70.1 hping statistic ---
1 packets transmitted, 0 packets received, 100% packet loss
round-trip min/avg/max = 0.0/0.0/0.0 ms

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