Martin, just trying to clarify the question.
A packet arriving at the final destination as the destination EID as the
destination IP address, and the source EID as the source IP address. If
something between the ETR and the destination EID generates an ICMP (of
any kind) it will be addressed to the source EID, not to the ETR. It
will go back presumably through the ITR 9which might be the same device
as the ETR). But it will simply be processed as an IP packet, not as an
ICMP for local consumption at the xTR.
If that is the case you meant, there is no ETR behavior for it.
If you meant some other case, can you please elaborate?
Thank you,
Joel
On 9/9/2020 5:36 PM, Martin Duke wrote:
Thanks Albert!
This all looks great, except one last thing that dropped out of the thread:
Sec 7.2 There is a fourth situation which can arise. If the ETR receives an
ICMP packet from an EID in its network. I have a couple of questions about what
should happen in this case:
>In this case the EID is locally attached to the xTR. Therefore, the
xTR has a locally configured MTU to reach the EID. So what is >written
in the section already covers this scenario.
I don't see why this is the case. In Sec 7.2, option 3 implies that the
ITR is not immediately attached to some endpoints. Why couldn't an ETR
receive an ICMP message from one of its destinations?
On Wed, Sep 9, 2020 at 5:56 AM Albert Cabellos
<[email protected] <mailto:[email protected]>> wrote:
Hi Martin
Just posted -34 per your comments:
https://www.ietf.org/rfcdiff?url2=draft-ietf-lisp-rfc6830bis-34
1) Removed duplicate paragraph in section 7
2) Added the following sentence for clarification of what happens
when N=0 and V=0: "/Finally, when both the N and V-bit are not set
(N=0, V=0), then both the Nonce and Map-Version fields are set to 0
and ignored on receipt/"
3) Removed the IPv4-only requirement in section 7.2. Please note
that this is in -35 since I missed it in the first place.
4) Added the following paragraph (yours, verbatim) at the end of
section 7.2:
/Please note that [RFC1191] and [RFC1981], which describe the use of
ICMP packets for PMTU discovery, can behave suboptimally in the
presence of ICMP black holes or off-path attackers that spoof ICMP.
Possible mitigations include ITRs and ETRs cooperating on MTU probe
packets ([RFC4821], [I-D.draft-ietf-tsvwg-datagram]), or ITRs
storing the beginning of large packets to verify that they match the
echoed packet in ICMP Frag Needed/PTB./
Albert
On Fri, Aug 14, 2020 at 12:17 AM Martin Duke
<[email protected] <mailto:[email protected]>> wrote:
As promised, here are my reconsidered thoughts about Section 7.2:
1) as agreed before, delete the restriction to IPv4 and restore
the other references to ICMPv6 in draft-31.
2) There is not an IETF consensus document that describes what I
feel to be the most secure way to do tunnel PMTU management. So
the current design is acceptable; however, there should be some
warning about the robustness issues here. Example text:
"Please note that [RFC1191] and [RFC1981], which describe the
use of ICMP packets for PMTU discovery, can behave suboptimally
in the presence of ICMP black holes or off-path attackers that
spoof ICMP. Possible mitigations include ITRs and ETRs
cooperating on MTU probe packets ([RFC4821],
[I-D.draft-ietf-tsvwg-datagram]), or ITRs storing the
beginning of large packets to verify that they match the echoed
packet in ICMP Frag Needed/PTB."
Feel free to re-word, of course.
This can either be in the section or mentioned in security
considerations with a pointer in 7.2.
Martin
On Thu, Aug 6, 2020 at 6:28 PM Joel M. Halpern
<[email protected] <mailto:[email protected]>> wrote:
Exploring Martin's second comment, I looked at section 7.2
of the draft.
I do not see any obvious reason why this section is
restricted to
IPv4. If there is a reason, we need to state it. If there
is no
reason, we should allow it for the v6 case as well.
Yours,
Joel
On 8/6/2020 6:24 PM, Martin Duke wrote:
> Hi Joel,
>
> I'm realizing that we may not have a consensus document
that provides
> good guidance on how to proceed. I'm going to consult
with a couple of
> SMEs and come up with a reasonable recommendation. This
shouldn't take
> any more than a couple of days.
>
> However the "IPv4 only" recommendation is just wrong and
should be reverted.
>
> On Thu, Aug 6, 2020 at 1:48 PM Joel M. Halpern
<[email protected] <mailto:[email protected]>
> <mailto:[email protected]
<mailto:[email protected]>>> wrote:
>
> Martin, I want to check one aspect of your response
about MTU handling.
>
> The entity which is originating the packets, and
receiving the ICMP
> responses, is the ITR. In most cases, the ITR is a
router. I do not
> know of any tunnel protocol for rotuers that expects
the routers to
> store state about the packets it has sent in the tunnels.
> As these are low-state tunnels, and as the packets
are those
> provided by
> the sources behind the ITR, I doubt that we can use
PLPMTUD, although I
> would be happy to be given enough information to find
I am wrong
> about that.
>
> I am somewhat confused as to what you would have us do.
> Yours,
> Joel
>
> On 8/6/2020 4:35 PM, Martin Duke wrote:
> > Hi Albert,
> >
> > thanks for the edits, and sorry for the delay!
We're not quite
> there on
> > a few of the items:
> >
> > Though first, there is now a duplicate paragraph
in Section 7.
> Please
> > delete one.
> >
> > On Fri, Jul 31, 2020 at 5:43 AM Albert Cabellos
> > <[email protected]
<mailto:[email protected]>
<mailto:[email protected]
<mailto:[email protected]>>
> <mailto:[email protected]
<mailto:[email protected]>
> <mailto:[email protected]
<mailto:[email protected]>>>> wrote:
> >
> >
> > On Fri, Jul 3, 2020 at 9:07 PM Martin Duke via
Datatracker
> > <[email protected] <mailto:[email protected]>
<mailto:[email protected] <mailto:[email protected]>>
> <mailto:[email protected] <mailto:[email protected]>
<mailto:[email protected] <mailto:[email protected]>>>> wrote:
> >
> > >
> >
> > > Sec 5.3 What is in the Nonce/Map-Version
field if both the
> N and
> > V bits are
> > > zero?
> > >
> >
> > There is no field then.
> >
> >
> > so the bits are set to zero, or is the LISP header
actually
> shorter by 3
> > octets?
> >
> >
> > >
> > > Sec 7.2 The stateful MTU design does not
incorporate any
> security
> > measures
> > > against ICMP spoofing. At the very least,
the ITR needs to
> make
> > sure that some
> > > fields in the outer IP and UDP headers are
hard to guess, and
> > that this
> > > information is stored to verify that the
ICMP message came
> from
> > on-path. If
> > > this is not possible, the design is not
safe to use over
> IPv4. If
> > > hard-to-guess information is not available
to be stored
> deeper in
> > the packet,
> > > then it is not safe over IPv6 either.
> > >
> >
> > The source UDP port is random. We have
therefore added the
> following
> > statement at the beginning of section 7.7:
> >
> > An ITR stateful solution to handle MTU
issues is
> described
> > as follows, this solution can only be used
with
> > IPv4-encapsulated packets:
> >
> >
> > This is backwards, and anyway inadequate.
> >
> > An off-path attacker can generate a fairly small
number of ICMP
> messages
> > to reduce the MTU to ridiculously low levels (e.g.
68 bytes), which
> > depending on tunneling overhead could render the
path unusable. The
> > defense against this is to either ignore ICMP
messages (instead
> using
> > PLPMTUD
> >
>
<https://datatracker.ietf.org/doc/draft-ietf-tsvwg-datagram-plpmtud/> to
>
> > find the MTU) or to compare the echoed information
the ICMP message
> > against the stored contents of the packet, where
obviously there
> needs
> > to be enough entropy to make it hard to guess.
Generally the port
> is not
> > sufficient entropy, since it takes fewer than 2^16
packets to
> take you
> > down, but admittedly there isn't much UDP-based
protocols can do
> about this.
> >
> > In IPv6, the router should include as much of the
packet as
> possible in
> > the ICMP packet, so the chance of guessing is low.
It's therefore
> it's
> > simply a matter of specifying that hosts should
store the packet
> payload
> > and do the validation step.
> >
> > In IPv4, the router is required to include the
first 8 bytes of
> the IP
> > payload (eg the UDP header), so all you have are
the IP and UDP
> headers.
> > Hosts should still do the validation.
> >
> > The main thing is to tell them to do that validation.
> >
> >
> > >
> > > Sec 7.2 There is a fourth situation which
can arise. If
> the ETR
> > receives an
> > > ICMP packet from an EID in its network. I
have a couple of
> > questions about what
> > > should happen in this case:
> > >
> >
> > In this case the EID is locally attached to
the xTR.
> Therefore, the
> > xTR has a locally configured MTU to reach the
EID. So what is
> > written in the section already covers this
scenario.
> >
> > >
> > > - How is this communicated to the sender of
the flow that
> > triggered the
> > > message? Is there an "outer" ICMP to the
ITR, and "inner"
> ICMP to
> > the source
> > > EID, both, or neither?
> > >
> > > - Is the ETR responsible for enforcing the
MTU to that EID for
> > subsequent flows?
> > >
> >
> >
> > I read 7.2 again and I don't see that it does.
According to this
> > section, what does the ETR do when it receives a
packet from the ITR
> > that exceeds the locally configured MTU?
> >
> > Martin
> >
> > _______________________________________________
> > lisp mailing list
> > [email protected] <mailto:[email protected]>
<mailto:[email protected] <mailto:[email protected]>>
> > https://www.ietf.org/mailman/listinfo/lisp
> >
>
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