We believe that your issue has been closed by the upload of
Version 1.4-1 of thc-ipv6 from Christian Hofstaedtler <ch@grml.org>.
The explanation is attached below

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Format: 1.8
Date: Mon, 14 Mar 2011 23:04:51 +0100
Source: thc-ipv6
Binary: thc-ipv6
Architecture: source amd64
Version: 1.4-1
Distribution: unstable
Urgency: low
Maintainer: Michael Gebetsroither <gebi@grml.org>
Changed-By: Christian Hofstaedtler <ch@grml.org>
Description: 
 thc-ipv6   - Tools to play with IPv6
Changes: 
 thc-ipv6 (1.4-1) unstable; urgency=low
 .
   * [325b41d] New upstream version 1.4 [Closes: issue948]
     - [05322ea] adapt for added binaries
     - [533f8f1] add missing tools to thc-ipv6.8
 .
   * General cleanups:
     - [7e0c7c3] Remove last patch and dpatch support
     - [f1068e8] don't ignore failures on clean
     - [304a85d] update to Standards-Version 3.9.1
     - [a6e3243] update manpage from upstream
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 f35f0c5ee6a6c23f5381a6c31629f5234b1e359e 6297 thc-ipv6_1.4-1.diff.gz
 139199ed4781f8411d4c9fe62ae89b48e5b189cf 613118 thc-ipv6_1.4-1_amd64.deb
Checksums-Sha256: 
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Files: 
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http://git.grml.org/?p=thc-ipv6.git now carries version 1.4.

The following packages have unmet dependencies:
  thc-ipv6: Depends: libssp0 (>= 4.1.1-12) which is a virtual package.

So we need a rebuild against current unstable I guess. But at the same time 
thc-ipv6-1.2.tar.gz is available at http://freeworld.thc.org/thc-ipv6/ - using 
GPLv3. If we want to ship thc-ipv6 with the upcoming stable release we should 
update our old thc-ipv6 version back from 2007.