C10k/PPPoE/IPv6 -> mess

Mohacsi Janos mohacsi at niif.hu
Fri Aug 4 11:11:19 CEST 2006

On Fri, 4 Aug 2006, Sebastian Abt wrote:

> Hi,
> we're actually having a somewhat weird scenario with "IPv6 on
> DSL"-services over here in Germany.  We started offering v6-only access
> services about 1.5 year ago, which went pretty smooth right from the
> start.  Now we encounter the problem that some customers can't use this
> service any longer with neither having something changed on their side,
> nor on our end.  Our DSL customers are brought to us via L2TP, so a
> typically setup looks like:
> customer <-- PPPoE --> DSLAM <----> LAC <-- L2TP --> ISP
> The problem is that Deutsche Telekom has replaced their ERXes with C10k
> LACs in some cities in Germany which don't handle encapsulated IPv6
> traffic correct.  While the ERXes were deployed, everyhting was fine
> (and still those aggregated by ERXes can use IPv6).
> When having a deeper look at the packets we saw that the C10ks put wrong
> values in the length-field of the PPPoE header (constantly 0x02,
> regardless of the actual payload size) while keeping all other things in
> good order.  The packets we are receiving on our LNS are all good.  We
> even did some testing with explicitly setting the L-Bit and the
> length-field in the L2TP header (which by default is not set on Cisco
> routers and even can't be switched on by software it seems), hoping the
> C10k would use these information and stop computing wrong values, but
> unfortunately that did not help in any way.
> This problem has been reproduced with two customers and three ISPs now.
> Unfortunately I don't know any details about the C10k's configuration or
> software being used and neither got anyone from Deutsche Telekom, nor
> from Cisco to pay attention to this bug, so my question is: has anyone
> on this list seen similar/exactly the same problems with PPPoE, C10ks

Yes we have similar problems for more than 1.5 years now. It is identified 
as BugID:  CSCsd13298. Cisco claims that this bug has been resolved: in a 
very recent IOS image 12.3(7)XI8 for Cisco 10000. Our problem lays in 
Hungarian Telekom - they are using 12.2(1x)BX? on C10K and they are not 
very willing to upgrade to the latest release. Hungarian Telekom also 
using Cisco 7300 and 7400 series for LAC purpose and with these boxes we 
don't have any problem.

If you succeed to convince Deutsche Telekom to test this new image (1 month 
old) please report it again.
Kindest Regards,

Janos Mohacsi
Network Engineer, Research Associate, Head of Network Planning
Key 00F9AF98: 8645 1312 D249 471B DBAE  21A2 9F52 0D1F 00F9 AF98

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