> On Sep 15, 2017, at 12:42 PM, Linda Dunbar <[email protected]> wrote: > > Sami, > Your wording only describes the scenario of one VTEP initiating the traffic, > but doesn’t describe the issues within the NAT device when receiving the > return encapsulated traffic from the remote VTEP. > > Specifically, if the Overlay Tunnel uses VxLAN encapsulation [RFC7348], IANA > assigned Port 4789 is used in the outer frames’ destination port field and > hashed value of inner packet is used in the outer frames’ source port field > [RFC 7348]. This approach can cause trouble when traversing NAT. > > In addition, your wording of “The Other VTEP … should use the translated UDP > source port as the destination port for the reverse traffic” is basically > eliminating the VxLAN RFC7348 encapsulation as a valid tunnel method (is it a > problem?) > > IMHO, this document should only describes the issue, but not the solutions. > > > Therefore, I suggest some minor changes to your wording: > ------------------------------------------------------------------------- > NAT traversing consideration: > > For scenarios where traffic over an NVO3 tunnel can be initiated from only > one VTEP side, and in the event that the NVO3 tunnel encapsulation traverse a > NAT GW. > The NAT GW will change both the VTEP src ip and udp port of the tunnel IP/UDP > header for the traffic initiated from one VTEP and expects the return traffic > to have certain destination udp port (instead of the RFC7348 specified 4789 > as the destination udp port). > > The other VTEP end of the tunnel, which MUST not be initiating any traffic > but only sending the return traffic, should use the translated UDP source > port as the destination port for the reverse traffic sent over the tunnel to > the translated NAT VTEP src address.
This requires maintaining state (of that source port) on the remote VTEP for that inner 5-tuple. And and as both ends are 'remote VTEPs' (to each other), they will both switch to different destination ports after the first encapsulated packet is received. And because the source port changes based on the inner 5-tuple, it means the remote end will send traffic to different ports, too. This is fraught with timeout problems in the NAPT. Static port forwarding is available on consumer and enterprise NAPT devices, and does not suffer these drawbacks. -d > > > Thanks, Linda > > From: Sami Boutros [mailto:[email protected]] > Sent: Thursday, September 14, 2017 4:37 PM > To: Linda Dunbar <[email protected]>; Dan Wing <[email protected]>; > [email protected] > Cc: NVO3 <[email protected]> > Subject: Re: Suggested wording for the "NAT Traversing Consideration" to be > added to the Section 6 of draft-ietf-nvo3-encap-00 > > Hi Linda, > > Thanks for the response. > > I will add a section as follow, please let me know if this is OK. > > NAT traversing consideration: > > For scenarios where traffic over an NVO3 tunnel can be initiated from only > one VTEP side, and in the event that the NVO3 tunnel encapsulation traverse a > NAT GW. > The NAT GW will change both the VTEP src ip and udp port of the tunnel IP/UDP > header. > > The other VTEP end of the tunnel, which MUST not be initiating any traffic > but only sending the return traffic, should use the translated UDP source > port as the destination port for the reverse traffic sent over the tunnel to > the translated NAT VTEP src address. > > Thanks, > > Sami > From: Linda Dunbar <[email protected]> > Date: Thursday, September 14, 2017 at 12:33 PM > To: Sami Boutros <[email protected]>, Dan Wing <[email protected]>, > "[email protected]" <[email protected]> > Cc: NVO3 <[email protected]> > Subject: RE: Suggested wording for the "NAT Traversing Consideration" to be > added to the Section 6 of draft-ietf-nvo3-encap-00 > > Sami, > > Sorry for the delayed response. > > Answers are inserted below: > > From: Sami Boutros [mailto:[email protected]] > Sent: Monday, September 11, 2017 12:24 PM > To: Linda Dunbar <[email protected]>; Dan Wing <[email protected]>; > [email protected] > Cc: NVO3 <[email protected]> > Subject: Re: Suggested wording for the "NAT Traversing Consideration" to be > added to the Section 6 of draft-ietf-nvo3-encap-00 > > Hi Linda, > > I have few clarifications and one question? > > When an overlay tunnel traverses an SNAT GW, the source address of the VTEP > will change to be the NAT source address. So, if we have an overlay tunnel > between 2 endpoints and we are doing SNAT in one direction. The other > endpoint will only see the translated NAT address. > > [Linda] Correct. China Telecom needs this type of deployment. > > > An overlay tunnel is bidirectional and doesn’t make an assumption that the > overlay traffic carried over the tunnel will only be initiated from one side. > > [Linda] The tunnel is bidirectional, but the traffic is initiated from the > CPE side for this scenario. > > > And it seems that what you are asking is to add directionality to the overlay > tunnel, in which one endpoint can not send any overlay traffic unless it > receives traffic from the other endpoint of the overlay tunnel, as well this > endpoint should use the UDP source port received from the other initiating > endpoint as the destination UDP port for the tunnel to accommodate for SNAT > traversal. > > [Linda] The so called “Overlay tunnel” is simply the encapsulation done by > both end points. In the scenario depicted, the traffic is initiated from the > CPE to the Gateway, and can be returned by the Gateway. Therefore, the tunnel > is bi-directionally. I don’t see any extra work needed to add > “directionality to the overlay tunnel” > > Linda > > Is my understanding correct? > > Thanks, > > Sami > > From: Linda Dunbar <[email protected]> > Date: Friday, September 8, 2017 at 2:31 PM > To: Dan Wing <[email protected]>, "[email protected]" > <[email protected]>, Sami Boutros <[email protected]> > Cc: NVO3 <[email protected]> > Subject: Suggested wording for the "NAT Traversing Consideration" to be added > to the Section 6 of draft-ietf-nvo3-encap-00 > > Sami, et al: > > Follow up the discussion during IETF 99, I took the stab putting together the > wording to describe why it is an issue for VxLAN encapsulated data frames > traversing NAT. I think this sub-section should be included in the Section 6 > of the draft-ietf-nvo3-encap. > > Linda Dunbar > > ---------------------------------------------------------------------- > > 6.10 NAT Traversal consideration > Here is an example of encapsulated traffic traversing NAT (Network Address > Translation) or, to be precise, NAPT (Network Address and Port Translation): > <image001.jpg> > Figure x – Scenario of Overlay Tunnel traversing NAT > > If the Overlay Tunnel uses VxLAN encapsulation [RFC7348], IANA assigned Port > 4789 is used in the outer frames’ destination port field and hashed value of > inner packet is used in the outer frames’ source port field [RFC 7348]. > Using different source port numbers is for achieving better traffic > distribution among multiple paths. This approach is fine within one data > center, but can cause trouble when traversing NAT. > Many NAT devices use Source Address and Port number of the data frames coming > from private addresses to derive the source port number for the frames sent > to the public network, as shown below (assuming VxLAN is used for > encapsulation between the CPEs and the Gateway). The NAT Public Source Port > H1/H2/H3/H4 can’t be the same, otherwise the NAT device can’t tell if the > return data frames should be sent to CPE1 or CPE2. > > Private Source Address > Private Source Port > Private Destination Port > NAT Public Source Addr > NAT public Source Port > NAT public Destination Port > CPE1 > A1 > 4789 > Public A > H1 > 4789 > CPE1 > A2 > 4789 > Public A > H2 > 4789 > CPE2 > A3 > 4789 > Public A > H3 > 4789 > CPE2 > A4 > 4789 > Public A > H4 > 4789 > > Per RFC 7348, the destination port number of the data frames returned from > the Gateway should be 4789. When the NAT device receive the data frames (with > the destination port = 4789) from the Public Network (i.e. from the Gateway > in the figure above), the NAT device has to drop the data frames as the > Destination Port 4789 is not one of H1/H2/H3/H4. > Of course, we can always modify the NAT devices to accommodate the VxLAN > encapsulated data frames. The problem is traversing the existing NAT devices > already deployed. > -------------------------------------- > > Sincerely hope the editors to draft-ietf-nvo3-encap can add those suggested > text to the draft. > > Linda Dunbar > > _____________________________________________ > From: Linda Dunbar > Sent: Thursday, July 13, 2017 2:31 PM > To: 'Dan Wing' <[email protected]> > Cc: NVO3 <[email protected]>; [email protected] > Subject: RE: [nvo3] draft-ietf-nvo3-encap-00 should add considerations of > traversing NAPT > > > Dan, > > Thanks for pointing out the Geneve's processing for traversing VxLAN. > > First of all I wasn't proposing using reduced set of source ports. I think > that the general document needs to add the consideration for traversing NAT > because it is an issue for IPv4. Joe Touch suggested adding the entropy in > the IPv6 flow ID as a solution for IPv6. > > As for your suggested approach in Geneve: > The reverse traffic is sent to the Geneve destination port (6081), and a > firewall or NAT or NAPT mapping is necessary for UDP/6081 traffic -- on both > datacenters, which both probably have their own underlay NAPTs. Those > firewalls (or NATs or NAPTs) need to have appropriate pinholes for UDP/6081. > > Does it mean all reverse traffic only use UDP port 6081? > Or all the NAT device convert the NVE’s UDP port 6081 to multiple port > numbers? > > Thanks, > Linda > > -----Original Message----- > From: Dan Wing [mailto:[email protected]] > Sent: Wednesday, July 12, 2017 6:09 PM > To: Linda Dunbar <[email protected]> > Cc: NVO3 <[email protected]>; [email protected] > Subject: Re: [nvo3] draft-ietf-nvo3-encap-00 should add considerations of > traversing NAPT > > > > On Jul 12, 2017, at 12:37 PM, Linda Dunbar <[email protected]> wrote: > > > > Sami, et al, > > > > > > > > The draft-ietf-nvo3-encap-00 is written very clear. > > > > > > > > However, the Section 6 (Common Encapsulation Considerations) should add a > > sub-section on the consideration of traversing NAPT. Encapsulated traffic > > could go to different data centers or WAN, which could go through Network > > Address Port Translation devices > > > > > > > > Using VxLAN as an example: VxLAN specification [RFC 7348] uses a set of > > Port numbers to achieve better traffic distribution among multiple paths, > > which is fine within one data center, but causing trouble when traversing > > NAPT. > > You're describing a problem with Geneve, which mimics VXLAN in that both of > them suggest using a wide range of UDP ports to help underlay ECMP and to > help receiver CPU load balancing, specifically this text of > https://tools.ietf.org/html/draft-ietf-nvo3-geneve: > > Source port: A source port selected by the originating tunnel > endpoint. This source port SHOULD be the same for all packets > belonging to a single encapsulated flow to prevent reordering due > to the use of different paths. To encourage an even distribution > of flows across multiple links, the source port SHOULD be > calculated using a hash of the encapsulated packet headers using, > for example, a traditional 5-tuple. Since the port represents a > flow identifier rather than a true UDP connection, the entire > 16-bit range MAY be used to maximize entropy. > > If a reduced set of source ports is used instead, as you propose, the ECMP > and CPU load balancing benefits are lost. That seems problematic. > > > NAPT use Port number to map back the source address. With a set of port > > numbers, NAPT can’t easily figure out the reverse direction traffic’s final > > IP addresses. > > The reverse traffic doesn't use the inverted 5-tuple. The reverse traffic is > sent to the Geneve destination port (6081), and a firewall or NAT or NAPT > mapping is necessary for UDP/6081 traffic -- on both datacenters, which both > probably have their own underlay NAPTs. Those firewalls (or NATs or NAPTs) > need to have appropriate pinholes for UDP/6081. > > > In addition, since the IP of packets change through NAPT device, it can > > mess up the learning of the peer NVE used in encapsulation. > > The underlay did the NAPT, so I don't see a problem with the NVE overlay > getting confused. Could you explain in more detail? > > > STUN can be used to get changed IP and port from NAPT device, but it > > requires NAPT device support STUN. > > NAPT devices are not expected to implement STUN. STUN is expected to be > implemented in the hosts behind the NAT and on a server on the other side of > the NAT (usually on a server on the Internet). See Figure 1 on page 6 of > https://tools.ietf.org/html/rfc5389#page-6. > > > That’s not available in some scenarios. Furthermore, it can’t solve the > > aforementioned five-tuple issue. > > > > > > > > VXLAN over IPSec may be used to deal with the above problems, > > Both Geneve and VXLAN run over UDP, and both use a fixed destination port > (rather than inverted 5-tuple) for return traffic. Not sure how VXLAN > succeeds at dealing with the above problems, but I would love to learn. > > > but IPSec brings up to 88 bytes of overhead plus the key distribution > > management, which can lower the efficiency. > > Should be able to use IPsec transport mode, which is more around 40 bytes > overhead. > > -d > > > > > > > > > > > > Suggestion: Add Section 6.10 Traversing NAPT consideration. > > > > I can help to provide the text if you all think the suggestion is > > acceptable. > > > > > > > > We can discuss more in Prague. > > > > > > > > Thanks, Linda Dunbar > > > > > > > > Huawei USA IP Technology Lab > > > > 5340 Legacy Drive, > > > > Plano, TX 75024 > > > > Tel: +1 469-277 - 5840 > > > > Fax: +1 469 -277 - 5900 > > > > > > > > _______________________________________________ > > nvo3 mailing list > > [email protected] > > https://urldefense.proofpoint.com/v2/url?u=https-3A__www.ietf.org_mailman_listinfo_nvo3&d=DwICAg&c=uilaK90D4TOVoH58JNXRgQ&r=IMDU0f3LtPMQf5XkZ06fNg&m=60T3yKN2I7oCxe8OH9mfZix-2ykSSjL-P-RoXCkZGdg&s=q7A_LzZuDp-yZnlA7Xw_N7yuLk4HO7K07jgl3Z78Ixg&e= _______________________________________________ nvo3 mailing list [email protected] https://www.ietf.org/mailman/listinfo/nvo3
