AH or ESP

Jack Kohn kohn.jack at gmail.com
Mon May 25 19:14:40 CDT 2009


Not really.

Currently, you cant even look at the ESP trailer to determine if its an
encrypted or an integrity protected packet, because the trailer itself could
be encrypted.

A router, by reading the next-header field from the ESP trailer can never be
sure that its an OSPFv3 packet inside since it wouldnt know whether the
packet is encrypted or not. One could have an encrypted packet inside, for
which the next-header field turns out to be 89, but that may not necessarily
mean that its an OSPFv3 packet. It could be a VoIP packet that just happens
to look like OSPFv3 once encrypted. There is no indication sent on the wire
that says that the packet is encrypted.

So, there is no way to identify/deep inspect/filter ESP packets unless
you're the recipient, which imo is the root cause of all heart burn in the
intermediate devices like firewalls, transit routers, etc.

A couple of solutions were thrown at the WG and the current one (wesp) was
selected as the best.

I agree that we should just throw out AH and stick to one protocol which has
been extensively tested. A quick scan through some of vendors data sheets
quickly reveals that most of them dont even provide support for AH.

Jack

On Tue, May 26, 2009 at 2:33 AM, Merike Kaeo <kaeo at merike.com> wrote:

> Yeah - the main issue with using ESP is that there's a trailer at end of
> packet that tells you more info to determine whether you can inspect the
> packet.  So you have to look at the end of the packet to see whether ESP is
> using encryption or null-encryption (i.e. just integrity protection).  Some
> vendors do have proprietary mechanisms in software for now which doesn't
> scale.  The work below will hopefully lock into a solution where hw can be
> built to quickly determine if ESP is used for integrity only.
>
> AH is not really widely used (except for OSPFv3 since early implementations
> locked in on AH when the standard said to use IPsec for integrity
> protection).  Note that a subsequent standard now exists which explicitly
> states that ESP-Null MUST be supported and AH MAY be supported.  But how
> many folks are actually running OSPF for a v6 environment and using IPsec to
> protect the communicating peers?  Some but not many (yet).
>
> Personally, I'd stick with ESP.  AH complicates matters (configuration,
> nested environments when you do decide to also use ESP for encryption maybe
> later, NAT) and while is isn't officially deprecated vendors don't test it
> as much as ESP - at interoperability tests it's not stressed, at least the
> ones I've been to.  Ask your vendor(s) what they think of the work below and
> see where they stand with implementing it.
>
> Be happy to answer any more questions offline.
>
> - merike
>
> On May 25, 2009, at 6:24 AM, Jack Kohn wrote:
>
>  Glen,
>>
>> IPSECME WG <http://www.ietf.org/html.charters/ipsecme-charter.html> at
>> IETF
>> is actually working on the exact issue that you have described (unable to
>> deep inspect ESP-NULL packets).
>>
>> You can look at
>> draft-ietf-ipsecme-traffic-visibility-02<http://tools.ietf.org/html/
>> draft-ietf-ipsecme-traffic-visibility-02>for
>> more details.
>>
>> Jack
>>
>> On Sat, May 23, 2009 at 5:06 AM, Glen Kent <glen.kent at gmail.com> wrote:
>>
>>> Yes, thats what i had meant !
>>>
>>> On Fri, May 22, 2009 at 10:46 PM, Christopher Morrow
>>> <morrowc.lists at gmail.com> wrote:
>>>
>>>>
>>>> On Fri, May 22, 2009 at 1:04 PM, Glen Kent <glen.kent at gmail.com> wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> It is well known in the community that AH is NAT unfriendly while ESP
>>>>> cannot
>>>>> be filtered, and most firewalls would not let such packets pass. I am
>>>>> NOT
>>>>>
>>>>
>>>> 'the content of the esp packet can't be filtered in transit' I think
>>>> you mean... right?
>>>>
>>>>  interested in encrypting the data, but i do want origination
>>>>> authentication
>>>>> (Integrity Protection). Do folks in such cases use AH or ESP-NULL,
>>>>>
>>>> given
>>
>>> that both have some issues?
>>>>>
>>>>> Thanks,
>>>>> Glen
>>>>>
>>>>>
>>>
>>>
>



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