Yeah, gotcha! So the problem here is fragmentation. I need to read some points of RFC to understand how fragmentations goes on IPSEC as I haven`t read anything yet. I thought router had something to handle such thing with the command "crypto isakmp fragmentation". I gotta understand what does this command
Thanks Piotr. On Fri, Jan 7, 2011 at 9:22 AM, Piotr Matusiak <[email protected]> wrote: > Bruno, > > The problem with AM is that it does not provide Identity protection (as > this info is in clear text) and may cause DoS issues because the responder > must generate KE material to send back to the initiator. > > I'm not saying that KE is protected in MM, the problem is with > fragmentation. If you want to send all those information in one packet this > may be an issue. In MM you're sending the same info in 3 different packets > (#1,#3,#5) from the Initiator perspective. In AM you must send it at once, > so that Proposals+KE+Identity(if it is certificate) may be a way larger than > 1500 bytes (or 1300 as it is sometimes configured on the IPSec Client). > > > Regards, > Piotr > > > 2011/1/7 Bruno <[email protected]> > >> Sure it does. Thanks Piotr. >> >> Which fragmentation issue could be seen? I didn`t think about it so far >> and have no clue why it would be a problem >> >> For instance, the cisco vpn client for whatever new connection, if you >> debug on the server side, we could see lots of proposals being sent. It >> seems it tries all possibilities. >> Wouldn`t it fall to fragmentation issue you referred? >> >> About security, as per my understanding, using RSA certificates, isn`t >> true that the attacker should get more informations to be able to guess the >> DH shared key? >> Even though it sends the Key material (in general goes in the 3rd and 4th >> message in MM and it goes in plain text as well) we would loose a lot using >> pre-shared key maybe with AG then with certificates. >> >> Well, sorry if the text got confused. Just tried to understand your points >> and discuss then >> >> >> On Fri, Jan 7, 2011 at 8:16 AM, Piotr Matusiak <[email protected]> wrote: >> >>> Gents, >>> >>> Let me chime in and add something to the discussion. >>> >>> Although it would be possible to use certificates with AM it brings a >>> little value in my opinion. >>> In AM everything is sent over with the very first packet including >>> Identity Payload. This means the certificate used as ID would be easily >>> accessed by everyone as this packet is not encrypted. There is no identity >>> protection at all in AM. >>> >>> The main reason for Cisco not to implement certificates with AM is the >>> potential problem with fragmentation. Note that the first packet contains >>> Proposals, KE material, and Identity, so if we would use certificates the >>> packet will be way above 1500 bytes. >>> For the same reason developers must NOT include all combination of >>> proposals - the packet length must be controlled. >>> >>> >>> Hope it will bring some light to that topic. >>> >>> Regards, >>> Piotr >>> >>> 2011/1/7 Bruno <[email protected]> >>> >>> Yeah, it wouldn't work as well >>>> >>>> My main config was: >>>> >>>> crypto isakmp pol 10 >>>> auth rsa-sig >>>> crypto isakmp profile AM >>>> initiate mode aggressive >>>> crypto map CMAP 10 isakmp-profile AM >>>> >>>> This results is the IOS jumping from AM to MM. If you change the isakmp >>>> policy to pre-shared keys, it will work with AM as expected >>>> >>>> I wonder if there is any weakness that made Cisco to avoid such >>>> behavior >>>> >>>> >>>> On Thu, Jan 6, 2011 at 10:37 PM, Jerome Dolphin <[email protected]>wrote: >>>> >>>>> Woops, no it doesn't help, forget I sent anything :) >>>>> >>>>> >>>>> On Fri, Jan 7, 2011 at 11:35 AM, Jerome Dolphin >>>>> <[email protected]>wrote: >>>>> >>>>>> Does this help? >>>>>> >>>>>> http://blog.ine.com/tag/aggressive-mode/ >>>>>> >>>>>> crypto isakmp profile AGGRESSIVE >>>>>> initiate mode aggressive >>>>>> self-identity fqdn >>>>>> keyring default >>>>>> ! >>>>>> crypto map VPN isakmp-profile AGGRESSIVE >>>>>> crypto map VPN 10 ipsec-isakmp >>>>>> >>>>>> >>>>>> On Fri, Jan 7, 2011 at 2:42 AM, Bruno <[email protected]>wrote: >>>>>> >>>>>>> At least it was what I understood reading it >>>>>>> Take a look on the 5.1 and 5.2 topics. >>>>>>> >>>>>>> 5.1 IKE Phase 1 Authenticated With Signatures >>>>>>> 5.2 Phase 1 Authenticated With Public Key Encryption >>>>>>> >>>>>>> Within each one you'll find how it should behave in MM and AM. >>>>>>> >>>>>>> >>>>>>> >>>>>>> On Thu, Jan 6, 2011 at 1:31 PM, Vybhav Ramachandran < >>>>>>> [email protected]> wrote: >>>>>>> >>>>>>>> Hello Bruno, >>>>>>>> >>>>>>>> I always thought that Digital certificates could only work in Main >>>>>>>> Mode. I'm yet to go through that RFC though.I'll go through it in a >>>>>>>> while. >>>>>>>> >>>>>>>> Cheers, >>>>>>>> TacACK >>>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> -- >>>>>>> Bruno Fagioli (by Jaunty Jackalope) >>>>>>> Cisco Security Professional >>>>>>> >>>>>>> _______________________________________________ >>>>>>> For more information regarding industry leading CCIE Lab training, >>>>>>> please visit www.ipexpert.com >>>>>>> >>>>>>> >>>>>> >>>>> >>>> >>>> >>>> -- >>>> Bruno Fagioli (by Jaunty Jackalope) >>>> Cisco Security Professional >>>> >>>> _______________________________________________ >>>> For more information regarding industry leading CCIE Lab training, >>>> please visit www.ipexpert.com >>>> >>>> >>> >> >> >> -- >> Bruno Fagioli (by Jaunty Jackalope) >> Cisco Security Professional >> > > -- Bruno Fagioli (by Jaunty Jackalope) Cisco Security Professional
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