Re: [v6ops] Extension Headers / Impact on Security Devices

Joe Touch <> Tue, 19 May 2015 21:00 UTC

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Date: Tue, 19 May 2015 13:59:43 -0700
From: Joe Touch <>
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Subject: Re: [v6ops] Extension Headers / Impact on Security Devices
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On 5/19/2015 1:48 PM, Brian E Carpenter wrote:
> On 20/05/2015 06:51, Joe Touch wrote:
>> On 5/19/2015 11:14 AM, Ted Lemon wrote:
>>> On May 19, 2015, at 12:15 AM, Fernando Gont <> wrote:
>>>> * The size of IPv4 options is very limited (well under 128 bytes)
>>>> * IYou only need to look at the IHL of the IPv4 packet to be able to
>>>> jump to the layer-4 protocol header. -- there's no such a thing in IPv6.
>>> I think it's generally agreed that we can expect devices to be somewhat limited as to how far into the packet they can peek on the fast path, and that we may need to tolerate a certain degree of non-compliance in such devices until Moore's law fixes the problem, or people become willing to pay more for it (which they probably won't absent some significant application).
>>> Maybe we should have an extension header that says where the transport header is... ;)
>> I briefly considered this at various times when this thread keeps
>> reappearing, but it would need to be another "HBH" header because it
>> needs to be examined and/or modified at any hop that modifies any other
>> extension header.
> No. RFC 2460 makes it clear that hops don't modify extension headers
> (except for shuffling within a routing header).

HBH headers are the exception and can be modified in-transit, which
would affect a transport-offset header.

FWIW, though, RFC2460 also clearly states:

   With one exception, extension headers are not examined or processed
   by any node along a packet's delivery path, until the packet reaches
   the node (or each of the set of nodes, in the case of multicast)
   identified in the Destination Address field of the IPv6 header.

If that were actually enforced, we would not need a transport-offset
header because routers would never be looking there.

> Also, there is a draft for this:
> (which does discuss the security issue; as with the evil bit, a firewall
> would be foolish to trust this option).

But fails to address the fact that this option might need to be updated
whenever any other extension header is modified.