I think we’re almost concluded so once more inline at <dd></dd>
On Oct 26, 2018, at 2:28 PM, Joel Halpern <[email protected]> wrote:
(resending, +spring as requested)
Thank you for the responses. I will respond in line, marked <jmh></jmh>. I
fear it will shortly get too deep, but the context is important.
I will rephrase here an issue from another thread that I ahve not seen your
comments on. If Node 9 is sending traffic to Node 1 (for example, the reverse
traffic for the traffic from 1 to 9 in the examples below), it presumably has
an SR Policy to be applied. The issue I raised before is the leakage issue. If
9 puts the SRH in its packet (as the document currently mandates), then it will
not be possible for 3 to remove the SRH. Thus, the SRH will leak.
Some have argued that is not a big deal. It seems to matter to me. But there
is an additional problem. A1 is not a SID. Therefore, 9 can not put A1 into
the SRH. If it can not put A1 into the SRH, and it does not encapsulate the
packet, where does it put A1.
<dd> Node 9 has a choice, encapsulate to node 3 or not.
If node 9 does not encapsulate, it will inform the destination of the segments
in the SRH and possibly leak them to intermediate nodes.
If node 9 does encapsulate, node 3 removes the outer header and node 1 would
not learn the segment list.
I think its choice should not be mandated in the draft. </dd>
Yours,
Joel
On 10/26/18 1:29 PM, Darren Dukes (ddukes) wrote:
Hi Joel, you’ve described sections titled “Intra SR Domain Packet”, “Transit Packet
Through SR Domain”, and "SR Source Nodes Not Directly Connected”.
I’ve parsed them inline to the sections of the draft defining them and given
more context where needed.
On Oct 22, 2018, at 8:49 PM, Joel M. Halpern <[email protected]> wrote:
Rephrasing using the example from 5.2. Assuming that 8 and 9 are SR Hosts (not
just hosts within the domain, they are capable of and expect to deal with SRHs,
and therefore have local SIDs, ...)
For traffic from 8 to 9 that needs an SRH, the SRH goes in the IPv6 header sent
my 8 to 9. When 9 processes the packet, it seems that it is the last SID,
figures out that there is no encapsulation, and send the TCP / UDP / QUIC
information to its internal protocols stacks.
Yes, this is Section 5.3.1 “Intra SR Domain Packet”.
<jmh>Agreed as far as it goes. However, the existence of S9 and A9 points to a
problem. Node 8 is trying to put on an SRH going through Sx, Sy, whatever for some reason.
It can't put A9 into the SRH, as AH is not a SID, it is an address. I presume node 8 got
S9 from whatever provided him the SR Policy that it is using. Does it simply use S9 as the
address for node 9, rather than A9 that it got from DNS? And does the TCP stack know that
this substitution is being made? (This is another example of a problem that goes away if
we always encapsulate.) </jmh>
<dd>Section 4.3.2 covers these questions, i.e. A9 can be placed in the SRH as the
last segment, and this section describes how it’s handled.</dd>
For traffic from 1 to 9, where 3 adds an SRH, that SRH still presumably ends at
9. 9 Receives the IP packet. Sees that it is addressed to itself. Sees that
the SRH is finished. And then notices that the next-header is IPv6. Unwraps
the header, checks that the inner destination address is also itself, and
passes the material carried by the inner header up to the appropriate stack.
So node 1 sends a packet to node 9 (A1,A9)
IF there is some steering into an SR Policy at node 3 to reach node 9, this is
identical to section 5.3.2 “Transit packet through SR domain”, except for
destination of A9 via node 9 instead of A2 via node 4.
Thus, 9 needs to be able to check for both cases. We at least need to tell
implementors that.
Well, 9 needs a SID S9 and Address A9. That is shown in Section 5.1 SID and
address representation.
<jmh>So, let us assume that 3 has an SR policy it wants to apply to the traffic from
A1 to A9. In this case, the S9 / A9 dichotomy is not a problem, I think. Node 3
encapsualtes the packet from A1 to A9, uses S3 as the source address of the encapsulating
header, and ends the SID list in the SRH with S9. The unspecified part is that node 9
needs to be prepared to receive such packets and do the double processing. It is
reasonable double processing. My only request here is that we tell folks they need to
support it. </jmh>
<dd>Actually, node 3 uses A3 as its source address, but that’s minor.
The double processing (lookup, do end processing, do another lookup) is
documented in Section 4.3.
Is there a need for more than what is currently specified? </dd>
There is a further complication. 9 seems to need to have an address that is a
valid SID, so it can be the last entry in the SRH from 8 to 9.
As described in the draft, Section 5.1 a node k has an address Ak and SID Sk.
So node 9 has a valid SID.
For traffic from 8 to 9, A9 is used as the destination as shown in section
5.3.1, 5.4 and 5.5.
However, if 1 were to send the packet to that SID for 9, router 3 would be
required by the rules we discussed in the other thread to discard the packet as
it is neither to prefix nor contains an HAMC.
And somehow, 8 and 1 need to each pick the right address to use for 9. (split
DNS maybe?) And 3 needs to be able to derive teh SID-formn address for 9 from
the non-SID form of the address so that it (3) can build a proper SRH to get
the packet to 9.
<jmh>I have retained your answer below for context, but I think that answers the
wrong question. I believe what is itnended is that only A9 appears in DNS. So Node 1 will
see 9 as A9, and will use that. S9 will appear in SR Policies about traffic to node 9, but
not in DNS. That is what we need. I wish it were clearer in the text. </jmh>
<jmh>If node 20 is generating SRHs with HMACs, then this is largely the same as the
case from 8 to 9, except that whomever creates the SR Policy that 20 is using needs to also
make sure that whatever the first SID is in teh list, it processes HMACs and is
recognizable to node 3 as doing such processing. I am guessing that the reason for allowing
internal nodes to do the processing is to move the verification load off the edge nodes.
It does create significant additional configuration complexity. </jmh>
<dd>We didn’t see a reason to restrict the HMAC processing to only edge nodes when it
was straight forward to define how they could be processed at non-edge nodes.</dd>
This is incorrect.
See Section 6.2.1 “SR Source Nodes Not Directly Connected” I will expand on the
example from that section.
Node 20 sends a packet to A9 with SR Policy <H7> and an HMAC provided to node
20 by some yet to be defined method. Resulting in packet sent from node 20
P: (A20,H7)(A9;SL=1)(payload)
Recall Hk is a SID at node k requiring HMAC verification, and it is covered by
Prefix-H.
Prefix-H is _not_ subject to ingress filtering at node 3.
Therefore the packet P destined to H7 is not subject to ingress filtering at
node 3.
P is forwarded to node 7, where H7 is processed and the HMAC verified.
If the HMAC can not be verified the packet is dropped, else it is forwarded to
the next segment and destination, A9.
Darren
Yours,
Joel
On 10/22/18 8:04 PM, Darren Dukes (ddukes) wrote:
inline.
On Oct 22, 2018, at 7:21 PM, Joel M. Halpern <[email protected]> wrote:
..
2) Now let us look at packets arriving at and actually destined for an SR Host
in the SR Domain where that packet has an SRH. If the packet is coming from
another SR Host, the SRH will be in the base header, and the host can simply
check it for any violations, and continue. But, if the packet came from
outside the domain, then it will have an encapsulating SRv6 header. So the
host has to detect this case, check and then peal off the encapsulating header,
and then process the received packet. Yes, it can do so. But nothing in teh
document tells implementors they have to deal with both cases.
Can you be more precise here. Perhaps use the example from section 5.2 or
6.2.1?
..
