Re: [Lwip] [IPsec] Suggestions in draft-mglt-lwig-minimal-esp

["Valery Smyslov" <[e-mail]>]

Hi,

 

IP fragmentation is a Bad Thing in general and it is better to

avoid it. With TCP traffic the TCP/IP stack

usually sends only unfragmented IP packets, so this is usually

not a problem (especially if you fool the stack that the MTU

is a bit smaller than real, so the packet is still within real MTU

size after applying ESP header/trailer/padding/ICV and external IP header).

 

The problem is worse with UDP. In this case it is an application

that decides how much data it wants to send in each datagram and there could

be fairly large UDP datagrams, that have to be IP fragmented.

In tunnel mode they can be either pre-fragmnted (before applying IPsec),

or post-fragmented (fragment the resulting ESP packet).

In transport mode it is not possible to pre-fragment packets.

 

In general, I think that pre-fragmenting is a bit better, than post-fragmenting.

So you’d better to apply ESP to each of IP fragments and send whole IP packets,

than apply ESP to a whole packet and then send it as a set of IP fragments.

In this case you at least verify each internal IP fragment on receiver,

before sending it to IP stack. In the other case you have to reassemble 

all the fragments before you can verify the ESP packet, and this gives

an attacker a nice target for DoS attack. However, the justification 

is weak, since the IP packets can always be fragmented en route (unless 

you set Don’t Fragment bit).

 

Regards,

Valery.

 

 

From: IPsec [mailto:[e-mail]] On Behalf Of Tobias Guggemos
Sent: Thursday, July 20, 2017 11:39 AM
To: 'Raja ashok'; [e-mail]
Cc: IPsecme WG; [e-mail]
Subject: Re: [IPsec] Suggestions in draft-mglt-lwig-minimal-esp

 

Hey Ashok,

thanks for your feedback.

For your first comment I tend to agree and I think we can add this to the draft!

For the second, I agree with your assumption that tunnels might appear in constrained scenarios (it’s actually one of our main
goals for ipsec/esp). However, I’m not sure if this recommendation to not use fragmentation is valid on a security side, why I’d
like to give the question to the ipsecme WG, if that does not open any other security issues? Or if there is anything else to
consider on that?

Thanks

Tobias

 

Von: Raja ashok [mailto:[e-mail]] 
Gesendet: Freitag, 14. Juli 2017 16:22
An: [e-mail]
Cc: [e-mail]
Betreff: Suggestions in draft-mglt-lwig-minimal-esp 

 

Hi Daniel & Tobias,

 

I gone through the lwIG draft for ESP. I am having some doubts and suggestions which are listed below. Please check and provide your
comments.

 

1)     For replay protection, RFC 4303 suggests to use 32 or 64 bit window. I feel in this draft, we can recommend to use 32 bit
window for replay protection.

 

2)     Tunneled ESP msg with fragmented IP header (in ESP payload) may leads to DoS vulnerability for a constraint receiver. RFC
4303 is suggesting this fragmentation as optional. So I feel we can mention as fragmentation and reassembly is not required to
support in tunneled IP header. As it can be handled by the IP header which carries ESP msg. I hope tunneled ESP msg might be
required in some scenarios of constraint devices also.

 

Regards,

Ashok

 

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Company_logo

Raja Ashok V K
Huawei Technologies
Bangalore, India
http://www.huawei.com 

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