Re: Last Call: <draft-ietf-6man-rfc1981bis-04.txt> (Path MTU Discovery for IP version 6) to Internet Standard

[Gorry Fairhurst <[e-mail]>]

The text below is not about tunnels - this is about  the operation of 
transport, and the quoted text is from the new UDP Guidelines ID.

On 15/02/2017 21:26, Joe Touch wrote:
> Hi, Gorry (et al.),
>
> Again, the following text should not drift into discussing how tunnels
> are handled IMO. That should be addressed in a different document (and I
> don't think it's troublesome at all if viewed correctly).
>
> Joe
>
>
> On 2/14/2017 9:23 AM, Gorry Fairhurst wrote:
>> - Introduces a significant vulnerability.  A rogue PTB message that
>> reduces the PMTU to a minimum, can result in a path too small to carry
>> an encapsulated packet. (Recently noted by Fernando Gont).
>>
>> Moreover, other layers view ICMP messages with suspicion and have long
>> noted the need to check ICMP payload and match only packets that
>> relate to actual 5-tuples in use (effectively reducing vulnerability
>> to off-path attacks). For example, the Guidelines for UDP, rfc5405bis,
>> state:
>>
>> " Applications SHOULD appropriately validate the payload of ICMP
>>    messages to ensure these are received in response to transmitted
>>    traffic (i.e., a reported error condition that corresponds to a UDP
>>    datagram actually sent by the application). …“

The comment below could easily be handled by something that clearly 
indicates the problem and points to the tunnel draft for guidance, I 
agree no need to go into algorithms/methods here.

>> - clearly handling this in IP-layer tunnels can be troublesome, but
>> that's a problem that should be described, not obscured.
>

Gorry