Re: [savi] Potential issue for all SAVI mechanisms?

[marcelo bagnulo braun <[e-mail]>]

Right, the question is how comon is for legitimate users to send 
NDP/DHCP/SEND fragmented packets? IS there any concrete real useful 
situacion where this happens?

If not, maybe we could simply say that SAVI will ignore the fragmented 
packets.
If yes, then it seems we may have a problem.

Regards, marcelo


El 22/06/11 06:35, Jun Bi escribió:
> In the Ethernet environment, the MTU is 1500, DHCP reply is not a 
> large packet and it won't be fragmented.
> Maybe the packet size of RA is large and might be fragmented, but it 
> is not processed in SAVI.
>
> thanks,
> Jun Bi
>
> -----原始邮件----- From: Joel M. Halpern
> Sent: Wednesday, June 22, 2011 8:17 AM
> To: Jun Bi
> Cc: Jean-Michel Combes ; SAVI Mailing List
> Subject: Re: [savi] Potential issue for all SAVI mechanisms?
>
> I do not think this is a sufficient answer.  Whether the device is a
> switch or a router, reassembling or maintaining packet state across
> fragements is a non-trivial undertaking.
>
> I can imagine some kludges to get around this, but they have broader
> impact than just SAVI.  (For example, rejecting first packets that do
> not have enough information to determine whether or not they are
> claiming to be RAs or DHCP replies.)
>
> Yours,
> Joel
>
> On 6/21/2011 9:56 AM, Jun Bi wrote:
>> Hi Jean-Michel,
>>
>> What we are talking about "savi switch" is a 2.5 layer switch (layer 2
>> switch in data plan with layer 3-aware in controll/management plan).
>> So what I know from switch vendor is that the 2.5 layer switch chip or
>> the stronger CPU can handel it.
>> For example, the chip can recongnize the Protocol ID field of IP packets
>> to recongznie HDCP or NDP packets (even in fragments),
>> then copy them to switch CPU. The CPU can handle it.
>>
>> The SAVI switch has been really implmented and deployed, so I did really
>> see any problem in real network.
>> BTW, it seems that SAVI switch doesn't snoop and process RA packets for
>> binding, so maybe RA packet is different.
>>
>> thanks,
>> Jun Bi
>>
>> -----原始邮件----- From: Jean-Michel Combes
>> Sent: Tuesday, June 21, 2011 9:37 PM
>> To: SAVI Mailing List
>> Subject: [savi] Potential issue for all SAVI mechanisms?
>>
>> Hi,
>>
>> Maybe you already know that there is a discussion on v6ops/6man MLs
>> about RA Guard evasion (cf.
>> http://www.ietf.org/mail-archive/web/ipv6/current/msg14204.html).
>> One of the methods to perform this evasion is fragmentation: it seems
>> that a L2 device would not be able to re-assemble all the fragments
>> without an important extra-cost and so would not be able to determine
>> whether or not the message is a Router Advertisement (cf.
>> http://www.ietf.org/mail-archive/web/ipv6/current/msg14240.html).
>>
>> Knowing that:
>> (1) In common use-case, SAVI device is a L2 device
>> (2) SAVI mechanisms are based on NDP/SEND/DHCP messages inspection
>>
>> I am wondering whether or not fragmentation would not impact strongly
>> SAVI specifications too: any fragmented NDP/SEND/DHCP message could
>> not update correctly the Binding Table and so what would be the
>> consequences?
>>
>> I would appreciate comments from WG members, especially
>> implementors/manufacturers, about this.
>>
>> Thanks in advance for your replies.
>>
>> Best regards.
>>
>> JMC.
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