Internet DRAFT - draft-saum-nvo3-pmtud-over-vxlan
draft-saum-nvo3-pmtud-over-vxlan
NVO3 S. Dikshit
Internet-Draft A. Sujeet Nayak
Intended status: Standards Track Cisco Systems
Expires: December 17, 2017 June 15, 2017
PMTUD Over Vxlan
draft-saum-nvo3-pmtud-over-vxlan-05
Abstract
Path MTU Discovery between hosts/VM/servers/end-points connected over
a Data-Center/Service-Provider Overlay Network, is still an
unattended problem. It needs a converged solution to ensure optimal
usage of network and computational resources for all hooked end-point
devices.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on December 17, 2017.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2.2. Solution Requirements . . . . . . . . . . . . . . . . . . 3
3. Problem Description . . . . . . . . . . . . . . . . . . . . . 3
3.1. IPv6 PMTUD Issues . . . . . . . . . . . . . . . . . . . . 4
3.1.1. Inaccurate MTU relayed to end hosts . . . . . . . . . 5
3.1.2. Packet_Too_Big not-relayed to host . . . . . . . . . 6
4. Solution(s) . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Discovery of end-to-end Path MTU . . . . . . . . . . . . 6
4.1.1. ICMP extensions, PMTUD on Vxlan . . . . . . . . . . . 7
4.1.2. Packet Path Processing . . . . . . . . . . . . . . . 7
4.1.3. ICMP(v6) Error Translation . . . . . . . . . . . . . 15
5. Multicast and Anycast Considerations . . . . . . . . . 25
6. Ecmp Considerations . . . . . . . . . . . . . . . . . . . . . 25
7. Security Considerations . . . . . . . . . . . . . . . . . . . 25
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 26
10.1. Normative References . . . . . . . . . . . . . . . . . . 26
10.2. Informative References . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
1. Introduction
There is an operational disconnect between underlay network
provisioned as the core network, and the overlay network which
intends to connect islands of customer deployments. The deployments
can range from cloud based services to storage applications or
web(over the top) servers hosted over virtual machines or any other
end devices like blade servers. Overlay network are provisioned as
tunnels leveraging Vxlan (and associated ones like gpe, geneve, gue),
NVGRE, MPLS and other overlay encapsulations.
The end hosts in a typical datacenter deployment are connected to
devices termed as ToR (top of rack devices). These are the
networking devices which encapsulate the packet in an Overlay
construct and relays it over Data center core network. Although a
ToR device MAY NOT always be a gateway for an overlay.
IPv6/IPv4 enabled hosts/end-points, triggering PMTUD, may not get the
right (or any) information from (over) the core network. This
document validates the solution for Vxlan core network (overlay) in a
data center deployment. This solution is equally applicable to any
other tunnel specific core network deployments.
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The proposal in this document, formulates an integrated approach
which falls inline with OAM modelling discussed in NVO3./>.
2. Requirements
2.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
When used in lowercase, these words convey their typical use in
common language, and they are not to be interpreted as described in
[RFC2119].
2.2. Solution Requirements
This section describes the advantages of the proposed solution,
considering deployment in a typical data center core network:
(a) Optimal use of bandwidth in core and client side network of
typical data center deployment.
(b) In case Vxlan Gateway nodes complies to this solution, it MAY
avoid black holing.
(c) All end host applications (like web servers) can tailor the MSS
accordingly against their respective transports.
(d) Facilitates seamless integration of IPv6 or dual stack
applications over IPv4 based overlays and vice versa.
(e) The proposed solution is applicable to all encapsulations
[RFC7348], [I-D.draft-ietf-nvo3-vxlan-gpe],
[I-D.draft-ietf-nvo3-gue], [I-D.draft-gross-geneve] and
[RFC7637]. Although the problem and solution refers to VXLAN
[RFC7348] as a use-case in this document.
3. Problem Description
In current vendor implementation(s) of Vxlan-Gateway/ToR-device or
other network devices, which form part of core data center network
and is configured with an overlay(tunnel) mechanism to transport
packets from one customer end point to another, are incapable of
relaying the errors encountered in routing/switching path in their
networks (underlay network) to the customer end points (hosts/vm/
blade-servers). This deems right, as core-network should be
transparent and water-tight with respect to leaking any public (core)
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network information to customer devices (and vice versa), thus
ensuring seclusion between different customers provisioning tunneled
over the same core network.
For example, the information carried in the IP header of a Vxlan
encapsulated packet is transparent to the payload (end-point
generated packet). Hence, any network-specific information related
to IPv6/IPv4 native functionality is carried to the end-point
devices, as is the case with an end-to-end private network. The
information generated in the core network devices while processing
packets destined-to/sourced-from end-point devices, need to be
percolated from underlay encapsulation to end customer specific
payload. This is something which is NOT directed by any standards,
and also NOT implemented by current deployment(s) of routers and
switches.
Considering the fact that future beholds IPv6-only datacenter
deployments, IPv6 PMTUD is one of the major casualties which can
linger on forever, in case not dealt with as of now. Although this
document intends to resolve PMTUD problem as a generic one across all
underlay encapsulations.
Note that terms "ICMP(V6)" or "icmp(v4)" are used in the document
with an intention to refer to both icmp and icmpv6, in case same
context applies to both.
3.1. IPv6 PMTUD Issues
As mentioned in the [RFC1981], IPV6 PMTUD is based on the "Packet too
big" icmpv6 error code, generated by the networking device which is
capable of generating such messages on encountering packet paths
which go over link with MTU size smaller than packet size.
There are problems getting this working when end-point device
initiates a "Path MTU Discovery" to remote end-point device. It may
lead to black-holing as per the current implementations.
The following bullets provides pointers to potential black holing of
PMTUD packets,
(1) Vxlan Gateway(or ToR) MAY not set the DF bit in the outer IP
header encapsulation.
(2) Vxlan Gateway(or TOR) is incapable of relaying icmp error
"Fragmentation Needed and Don't Fragment was Set", generated by
IPv4 enabled core network device (underlay network), to IPv6
enabled end-point host/vm/server(source of the original packet).
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The problems are discussed in detail in the following sub-sections.
3.1.1. Inaccurate MTU relayed to end hosts
Figure 1 depicts the topology referenced in the document for
explaining the problem statement and the solution.
+----------+ +----------+
| H1 | | H2 |
| | | |
|(H1_IPv6) | |(H2_IPv6) |
+----------+ +----------+
| |
| |
+------------+ +----------+ +------------+
|(VtepA_IPv6)| | | |(VtepB_IPv6)|
| VtepA | | R1 | | VtepB |
|(VtepA_IPv4)|---| (R1_IPv4)|---|(VtepB_IPv4)|
+------------+ +----------+ +------------+
Figure 1. L3 Overlay
LEGEND:
MAC address : <Node_name>_MAC
IP address : <Node_name>_IPv4
IPv6 address: <Node_name>_IPv6
<Node_name> : node names in the above topology are
H1, VtepA, R1, VtepB, H2.
VtepA, VtepB: Vxlan gateways to core network
R1: Intermediate router in underlay network
H1,H2: End-point devices communicating withe each other
H1 and H2 are the end point hosts in different subnet connected over
Vxlan Overlays in core network. The Vtep tunnel end-points MAY be
ToR devices are christened as VtepA and VtepB, reachabile over an
underlay IPv4 network. VtepA and VtepB are dual stack enabled and
act as Vxlan gateways to connected hosts in this specific example.
Link mtu between VtepA, R1 and VtepB is 1300 bytes, where as for the
link between H1 and VtepA, H2 and VtepB, is 1500 bytes.
H1 sends out a packet obliging to 1500 bytes MTU packet size
containment over the H1 and VtepA link. VtepA encapsulates the
packet with (Vxlan + UDP) header and outer IP header corresponding to
underlay reachability to destination tunnel end-point, that is VtepB,
to reach out to H2.
If size of encapsulated packet to be send over the link VtepA-R1
exceeds the MTU (1300 bytes). IPv4 packet with (IP header + UDP
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header + Vxlan header + Original L2 Packet from H1 containing the
IPv6 Payload) SHOULD be fragmented. In case Vxlan gateway, VtepA,
does not sets the DF-bit in the outer IP header, the packet gets
fragmented, with the reassembly done at the egress gateway (VtepB).
The re-assembled packet is routed by VtepB to H2. This can
potentially lead to inaccurate Path MTU calculation at H1. H1
assumes it to be 1500 bytes as no icmp error is received. This opens
the door for fragment/reassembly and more cpu cycles on networking
devices in core network.
3.1.2. Packet_Too_Big not-relayed to host
In figure 1, assume that link between VtepA and R1 is 1500 as the
only change from the figure 1 topology. Hence the packet send by H1,
leads to VtepA setting the DF-bit in the outer IP header(as part of
Vxlan Encapsulation). When R1 receives the packet and the routing
table lookup points to the outgoing link with mtu size R1_VtepB_MTU
bytes, less than the packet size (1500 bytes). As DF-bit is set, R1
generates ICMPv4 error directed towards the src-ip (VtepA_IPv4). It
encapsulates the inner PDU of the original packet. However, VtepA
drops the icmp error packet and fails to relay it to H1. This leads
to black-holing.
The above two sub-sections lay down potential problems for IPv6 Path
MTU Discovery mechanism in an Overlay network. Although these
problem are generic to any combination of underlay and overlay
network types (IPv4 or IPv6), the use-case topology in this document
is specific to IPv6 end-point devices connected over Vxlan network,
wherein, the underlay is connected over IPv4 network, unless
mentioned specifically.
4. Solution(s)
4.1. Discovery of end-to-end Path MTU
Since Vxlan Gateway (can be a ToR device) is the one, which
encapsulates the Vxlan (or any other overlay) header onto the packet
traversing through the overlay network and also decapsulates the
overlay header for packets egressing out of same and heading towards
the end devices, the solution becomes more apt to be installed on
devices playing such role.
Firstly, It is a MUST that Vxlan gateways (VtepA, VtepB or ToR
device) SHOULD set the DF-bit in Outer header encapsulation for
client packets that are wrapped with vxlan, related encapsulation,
for Path MTU Discovery. Thus ensuring that ICMP error packet is
generated for packet size exceeding the link MTU in underlay network.
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Secondly, it is MUST that Vxlan gateway devices translates the ICMP
error "Destination Unreachable" with code 'Fragmentation Needed and
Don't Fragment was Set', into a ICMPv6 error 'Packet too big' packet.
This mandates that original packet carried in the icmp error message
MUST carry information about the inner payload(original packet), and
it is an IPv6 Packet, originated from the end-point device (H1 for
VtepA in figure 1), connected to the Vxlan gateway over L3/L2
network.
Thirdly, it is MUST that Vxlan gateway devices translates the ICMPv6
error 'Packet too big' into a ICMP error 'Destination Unreachable'
with code 'Fragmentation Needed and Don't Fragment was Set' packet.
Successfully translation mandates that, original packet carried in
the icmp error message gives information about the inner payload
(original packet), and it is an IPv4 packet, which originated from
the end-point device connected to gateway over L3/L2 network.
Fourthly, incase both, the client side network connected to Vxlan
Gateway and the underlay network are same, that is, either both are
ipv4 or both are ipv6, then icmp error code error translation is NOT
required. Rest of the process to retrieve original packet is
identical.
4.1.1. ICMP extensions, PMTUD on Vxlan
This solution leverages extensions in ICMP and ICMPv6 standards,
[RFC4884], for the maximum size of the original packet that can be
encapsulated in ICMP error message with code as "Fragmentation
Required(icmp)" or "Packet too big(icmpv6)" respectively. As the
host info is encapsulated in the inner payload, this requires
additional bytes of data in icmp packet: (Outer IP Header + UDP
Header + Vxlan + Inner L2 Header + Inner IPv6 SRC/DST IPs).
In case Vxlan core network is provisioned over IPv6 underlay, then
similar extensions are applicable to icmpv6.
The processing of ICMP(V6) packet is extended from the current
standards of 'non-delivery of ICMP(v6) packets to upper-layers on
Vxlan gateways' to 'relaying it to the end-point devices'.
4.1.2. Packet Path Processing
Packet Path handling and processing is explained in this section.
The assumptions are made with respect to network topology mentioned
in Section 3.1.1. The packet format in each flow captures packet
fields which are significant with respect to this solution. To
understand the solution, the packet flow is explained which leads to
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generation of ICMP or ICMPv6 error by intermediate node in underlay
network.
IPv6 packet is sent by host H1 destined to host H2, both are in
different IPv6 subnets.This packet is referred to as P1 in the
document.
+----------------------------------------------------+
H1--|L2_Hdr(14 bytes): src-mac:H1_MAC, dest-mac:VtepA_MAC|-->VtepA
+----------------------------------------------------+
|IPv6_Hdr(40 bytes): src-ip:H1_IPV6, dest-ip:H2_IPv6 |
+----------------------------------------------------+
|Host/App specific Payload |
+----------------------------------------------------+
Figure 2a. Packet P1 sent by host H1 to host H2
VtepA re-writes the mac addresses in 'P1' as part of Vxlan
encapsulation. This encapsulation is referred as 'P2' in the
document.
+------------------------------------------------------+
H1--|L2_Hdr(14 bytes):src-mac:VtepA_MAC, dest-mac:VtepB_MAC|-->VtepA
+------------------------------------------------------+
|IPv6_Hdr(40 bytes): src-ip:H1_IPV6, dest-ip:H2_IPv6 |
+------------------------------------------------------+
|Host/App specific Payload |
+------------------------------------------------------+
Figure 2b. Packet P1 re-written by VtepA
4.1.2.1. Packet Processing at Vxlan Gateway
Processing at VtepA, in packet path from H1 to H2.
(1) VtepA(Vxlan gateway) performs the Vxlan encapsulation over the
packet received from H1, based on route lookup. The detail for
encap are mentioned in [RFC7348].
(2) VtepA MUST set the DF-bit in the Outer IP header.
(3) Since the MTU of outgoing link is more than the packet, packet
is sent out towards the underlay next hop, R1.
(4) P3 packets encapsulation is shown in figure 3. P3 may find a
reference without outer header encapsulation [RFC7348] provides
details of the vxlan encapsulation.
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+----------------------------------------------------------+
VtepA-|L2_Hdr(14bytes):src-mac:VtepA_Mac, dest-mac:R1_MAC |-->R1
+----------------------------------------------------------+
|IPv4_Hdr(20 bytes):src-ip:VtepA_IPv4,dest-ip:VtepB_IPv4,DF|
+----------------------------------------------------------+
|UDP(8 bytes): src-port: ephemeral-port, dest-port: 4789 |
+----------------------------------------------------------+
|Vxlan(8 bytes): Vxlan network identifier |
+----------------------------------------------------------+
|P2 packet (refer to H1 to VtepA flow for details of P1) |
+----------------------------------------------------------+
Figure 3. Vxlan Encap packet sent by Vxlan Gateway to core
4.1.2.2. Underlay Generates ICMP error
In case the underlay is ipv6 and not ipv4, icmpv6 error is generated.
Processing at R1:
(1) Packet Size (1500 bytes) is more than the outgoing link's mtu
(1300 bytes) and DF-bit is set in the Outer IPv4 header added as
part of Vxlan encapsulation at VtepA.
(2) R1 MUST generate icmp error message (Destination Unreachable)
with error code (Fragmentation Needed and Don't Fragment was
Set). For ease of solution description, mtu is assumed to be
symmetric over the reverse path, hence reverse path mtu from R1
to VtepA is 1500 bytes. ICMP(v6) error message MUST include MTU
of link between R1 and VtepB.
(3) In a nut shell, the ICMP PDU encapsulation SHOULD be performed
as mentioned in [RFC4884] , [RFC4443]. These standards atleast
ensure, that original packet carried in icmp error PDU captures
enough bytes to include the inner packets IPv6 header atleast.
The capture of application specific details depends on the size
of the Optional header in the original packet (generated by H1
as in Figure 2b) and subsequent transport header. This helps
Vxlan Gateway to trace(L3 reachability) the original packet
generator (end-point device) atleast and translate icmp error
generted by underlay into icmpv6 one and relay it to end-point
device. The length field in ICMP PDU, include the maximum
possible length permissible in reverse path MTU
For simplicity, not including the original packet header in the flow
diagram in figure 4. ICMP PDU details are depicted in the follow up
figure 5.
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+-----------------------------------------------------------+
R1-|L2_Hdr(14 bytes): src-mac:R1_MAC, dest-mac:VtepA_MAC |-->VtepA
+-----------------------------------------------------------+
|IPv4_Hdr(20 bytes): src-ip:R1_IPv4, dest-ip:VtepA_IPv4 |
+-----------------------------------------------------------+
|ICMP PDU,type:3,code:4,R1_VtepB_MTU, P3(No outer L2 Header)|
+-----------------------------------------------------------+
Figure 4. Flow diagram from R1 to VtepA
The details of ICMP PDU are in the following figure. Type '3' is
"Destination Unreachable". Code '4' is "Fragmentation Needed and
Don't Fragment bit is set".
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4s 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Type=3 | Code=4 | Checksum | ICMP
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type=3
| unused | Length | Next Hop Mtu = R1_VtepB_MTU | Code=4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Ver=4|IHL=5 | TOS | Total length | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Id |Flags| Fragment Offset | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| TTL | Protocol=UDP | Header Checksum |(Outer)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Max 40
| src-ip : VtepA_IPv4 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| dest-ip : VtepB_IPv4 | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Source UDP Port (ephemeral) | Dest UDP Port = 4789 (Vxlan) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+8 bytes
| Length | Checksum | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| | | | | | | | | Reserved | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+8 bytes
|Vxlan Network identifier (VNI) | Reserved | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -------
| Inner Packet Dest-Mac = VtepB_MAC | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | Inner Packet Src-Mac = | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Inner
| VtepA_MAC |14 byte)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Inner Vlan if present |Ethtype = 0X86dd (IPv6) | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
|Ver=6 |Traffic Class | Flow Label | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
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|payload length |Next Header | Hop Limit | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| src-ipv6 = H1_IPv6 |IPv6
| |Header
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| dest-ipv6 = H2_IPv6 | |
| | |
| | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| ~ Optional Headers and transport header/Payload ~ | Varies
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
Figure 5. ICMP PDU Original Packet Capture in Detail
4.1.2.3. Relay ICMP(v6) Error to End Devices
This sub-section can also be generalized as: "handling of icmp
errors, which are generated by underlay network in response to end-
device packets, by Vxlan Gateway".
Processing at VtepA: Processing of icmp error message with code
(Fragmentation Needed and Don't Fragment was Set):
(1) The icmp error is processed by Vxlan gateways as per the
standards defined in [RFC1981] , [RFC4884] and [RFC4443] .
(2) If error code is (Fragmentation Needed and Don't Fragment was
Set), it SHOULD perform further inspection of the original
packet, P3(ethernet payload without its header) carried as data
in ICMP PDU in extension to standards referred in previous
bullet. The extension processing MUST be done prior to taking a
decision to either drop the packet or deliver to upper-layer
protocols.
(3) In extension to above, Vxlan gateway device SHOULD perform the
vxlan decap as defined in [RFC7348], to arrive at the inner
packet (P2, original packet with VtepA rewrite). The underlay
encap is not carrying the layer-2 header in the icmp error
packet. Once this processing is done, P2 is the packet which
needs attention now, as it carries the credentials of actual
host which should receive the relayed icmp packet.
(4) The layer-3 payload type SHOULD be verified using ethernet type
field in ethernet header. In case it point to IPv6, src-ipv6
field should be picked up to check for reahability, as the icmp
packet MUST be sent to original sender, that is, H1. In case H1
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is reachable, ICMP packet SHOULD be constructed as mentioned in
the following bullet.
(5) Now that P2 is out in the open, it's L2 header is decapsulated,
and the leftover, in the figure 6, is run through the icmpv6
processing as mentioned in [RFC4443].
(6) It SHOULD generate ICMPv6 error message with type (Packet too
big) destined to H1_IPv6, that is inner ipv6 packet's source
ipv6 address. The mtu 'R1_VtepB_MTU' is copied from icmp error
packet recieved from the underlay.
(7) The IPv6 header is constructed from original payload as shown in
figure 5. The source ipv6 address is picked as local ipv6
address "VtepA_IPv6". The destination ipv6 address is set as
the "src-ipv6" in original payload, H1_IPv6. The Next Header is
set as "58" which denote ICMPv6. The derivation of ethernet
header is based on next hop to mac address mapping as is
performed in any L3 lookup. The follow up figure 9, shows the
icmpv6 error packet sent out to node H1. H1 is the original
IPv6 packet generator as mentioned in Figure 2b.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
|Ver=6 |Traffic Class | Flow Label | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
|payload length |Next Header | Hop Limit | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| src-ipv6 = H1_IPv6 | Inner
| | IPv6
| | 40 byt)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| dest-ipv6 = H2_IPv6 | |
| | |
| | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| ~ Optional Headers and Transport/Application Payload ~ | Varies
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
Figure 6. Original IPv6 Packet sent from H1 directed to H2
Figure 6 gives a typical IPv6 format sent by end-host, H1 towards H2
and encapsulated by Vxlan gateway, to translate the icmp error
generated by underlay hop, R1, to the one understood in right context
by H1.
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0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Type=2 | Code=0 | CheckSum | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type=2
| Mtu = R1_VtepB_MTU | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
|Ver=6 |Traffic Class | Flow Label | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
|payload length |Next Header | Hop Limit | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| src-ipv6 = H1_IPv6 | Orig
| | Packet
| |40 byte)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| dest-ipv6 = H2_IPv6 | |
| | |
| | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -----
| ~ Optional/Transport Headers and Application Payload ~ |varies
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
Figure 7. ICMPv6 "Packet Too Big" PDU relayed
to H1 by Vxlan Gateway (VtepA)
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Dest-Mac = H1_MAC | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | Inner Packet Src-Mac = | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+eth hdr
| VtepA_MAC |14 byte)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Inner Vlan if present |Ethtype = 0X86dd (IPv6) | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
|Ver=6 |Traffic Class | Flow Label | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
|payload length |Next Hdr = 58 | Hop Limit | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| src-ipv6 = VtepA_IPv6 | IPv6
| |header
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| dest-ipv6 = H1_IPv6 | |
| | |
| | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
Figure 8. Ethernet and IPv6 encap for ICMPv6 PDU mentioned in
figure 7
The translated icmp packet encapsulation looks similar to, figure 7
and figure 8 put together in reverse order. The flow diagram in
figure 9 gives a concise form of "packet too big" icmpv6 error
relayed by VtepA (Vxlan Gateway) towards H1 (end point device).
+--------------------------------------------------------+
VtepA--|L2_Hdr(14): src-mac:VtepA_MAC and Dest_Mac: H1_MAC |-->H1
+--------------------------------------------------------+
|IPv6_Hdr(40 bytes): src-ip:Vtep_IPv6, dest-ip:H1_IPv6 |
+--------------------------------------------------------+
|ICMPv6: Packet_Too_Big, mtu, data: first 128 bytes of P3|
+--------------------------------------------------------+
Figure 9. Flow diagram: VtepA to H1
There are few more potential flows worth mentioning in this section.
These cases are related to, icmp error getting generated from,
ingress Vxlan gateway (VtepA) and egress Vxlan gateway (VtepB) with
respect to packet sent from H1 to H2. For ingress Vxlan gateway
(VtepA) case, the legacy IPv6 PMTUD rules from [RFC4443] SHOULD be
applied as no Vxlan encap is involved.
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Where as, egress Vxlan gateway (VtepB) SHOULD send packet P3 (without
L2 header) in the icmp data, even though mtu calculation MAY be done
post vxlan decapsulation. That is when the outgoing link is
identified as the one from VtepB to H2. It MAY buffer packet P3
prior to lookup based on inner packet (P2) credentials, so that P3
can be encapsulated in the icmp packet. This also ensures the packet
format consistency, when accessed at the VtepA for translation before
relaying it to H1.
4.1.3. ICMP(v6) Error Translation
This section specifically mentions about ICMP and ICMPv6 packet
translation, generated in an underlay network to the one which is,
understood by the end point device, with encapsulation aligning with
the network-type(IPv4 and IPv6), end-point device and underlay is
provisioned with. The last leg processing mentioned in previous sub-
section is specific to the topology mentioned in Section 3.1.1.
However, this subsection elaborates on all possible topology
combination of underlay and end-device networks with respect to IPv4
or IPv6. The explanation provided in form of figures for error
generated by underlay and the translated one relayed to the end-point
device by Vxlan gateway.
(a) End-Point is IPv6 connected and Underlay is IPv4 provisioned.
(b) End-Point is IPv4 connected and Underlay is IPv6 provisioned.
(c) Both End-Point and Underlay are provisioned with IPv6.
(d) Both End-Point and Underlay are provisioned with IPv4.
4.1.3.1. End-Point is IPv6 connected and Underlay is IPv4 provisioned
This case is similar to the last leg processing described in
Section 4.1.2 and does not needs any more description.
4.1.3.2. End-Point is IPv4 connected and Underlay is IPv6 provisioned
Topology drawn in figure 10, provides for the icmpv6 PDU encap
generated by R1. H1_IPv4 and H2_IPv4 are in distinct ipv4 subnets.
R1_IPv6 represents IPv6 addresses falling in both subnets connecting
to VtepA and VtepB.
Another difference between an IPv4 and IPv6 underlay is that for IPv6
underlay there is no concept of DF-bit. The fragmentation can only
be done at ingress. At all other underlay nodes "Packet too big"
icmpv6 error is generated. Vxlan Gateway SHOULD ensure that
fragmentation is avoided at Vxlan Gateway and icmp error is sent back
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to H1. This procedure is applicable if and only if, original packet
contains DF-bit set in it's IP header.
+----------+ +----------+
| H1 | | H2 |
| | | |
|(H1_IPv4) | |(H2_IPv4) |
+----------+ +----------+
| |
| |
+------------+ +----------+ +------------+
|(VtepA_IPv4)| | | |(VtepB_IPv4)|
| VtepA | | R1 | | VtepB |
|(VtepA_IPv6)|---| (R1_IPv6)|---|(VtepB_IPv6)|
+------------+ +----------+ +------------+
Figure 10. L3 Overlay
LEGEND:
MAC address : <Node_name>_MAC
IPv4 address: <Node_name>_IPv4
IPv6 address: <Node_name>_IPv6
<Node_name> : node names in the above topology are
H1, VtepA, R1, VtepB, H2.
VtepA, VtepB: Vxlan gateways to core network
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Type=2 | Code=0 | Checksum | ICMPv6
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type=2
| Next Hop Mtu = R1_VtepB_MTU | Code=0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
|Ver=6 |Traffic Class | Flow Label | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
|payload length |Next Hdr | Hop Limit | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| src-ipv6 = R1_IPv6 | IPv6
| |40 byte)
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| dest-ipv6 = VtepA_IPv6 | |
| | |
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| ~ Extension Headers ~ (payload type is UDP) | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
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| Source UDP Port (ephemeral) | Dest UDP Port = 4789 (Vxlan) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8 byte
| Length | Checksum | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| | | | | | | | | Reserved | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8 byte
|Vxlan Network identifier (VNI) | Reserved | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Inner Packet Dest-Mac = VtepA_MAC | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | Inner Packet Src-Mac = | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+eth hdr
| VtepB_MAC |14 byte
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Inner Vlan if present |Ethtype = 0X0800 (IPv4) | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Ver=4|IHL=5 | TOS | Total length | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Id |Flags| Fragment Offset | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| TTL | Protocol | Header Checksum | Orig
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Hdr
| src-ip : H1_IPv4 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| dest-ip : H2_IPv4 | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| ~ transport-header and Application specific Payload ~ | varies
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
Figure 11. ICMPV6 PDU Sent by R1 to VtepA
R1 sends an icmpv6 error "Packet Too Big" directed towards VtepA.
The icmpv6 PDU is shown in Figure 11. VtepA receives the packet with
this icmpv6 PDU and translates it to icmp PDU with type "Destination
Unreachable" and code "Fragmentation Needed" before relaying it to H1
over ipv4 network. Figure 12, reflects the relayed packet sent by
VtepA to H1. All other references SHOULD be taken as it is from
Section 4.1.2.
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0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Dest-Mac = H1_MAC | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | Inner Packet Src-Mac = | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+eth hdr
| VtepA_MAC |14 byte)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Inner Vlan if present |Ethtype = 0X0800 (IPv4) | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Ver=4|IHL=5 | TOS | Total length | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Id |Flags| Fragment Offset | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| TTL | Protocol=1 | Header Checksum | IPv4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| src-ip : VtepA_IPv4 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| dest-ip : H1_IPv4 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Optional Header | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Type=3 | Code=4 | Checksum | ICMP
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type=3
| unused | Length | Next Hop Mtu = R1_VtepB_MTU | Code=4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Ver=4|IHL=5 | TOS | Total length | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Id |Flags| Fragment Offset | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| TTL | Protocol | Header Checksum |Orig
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+iPv4
| src-ip : H1_IPv4 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| dest-ip : H2_IPv4 | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Optional and Transport Header and Application data | varies
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
Figure 12. ICMPv4 error Packet relayed to end point Host, H1
4.1.3.3. Both End-Point and Underlay are provisioned with IPv6
Topology is mentioned in Figure 13 with minor changes along with the
legend. Figure 14, outlines the icmpv6 PDU, encapsulation generated
by R1. H1_IPv6 and H2_IPv6 in different ipv6 subnets. R1_IPv6
reflects both subnets connecting to VtepA and VtepB.
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+----------+ +----------+
| H1 | | H2 |
| | | |
|(H1_IPv6) | |(H2_IPv6) |
+----------+ +----------+
| |
| |
+------------+ +----------+ +------------+
|(VtepA_IPv6)| | | |(VtepB_IPv6)|
| VtepA | | R1 | | VtepB |
|(VtepA_IPv6)|---| (R1_IPv6)|---|(VtepB_IPv6)|
+------------+ +----------+ +------------+
Figure 13. L3 Overlay
LEGEND:
MAC address : <Node_name>_MAC
IPv6 address: <Node_name>_IPv6
<Node_name> : node names in the above topology are
H1, VtepA, R1, VtepB, H2.
VtepA, VtepB: Vxlan gateways to core network
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Type=2 | Code=0 | Checksum | ICMPv6
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type=2
| Next Hop Mtu = R1_VtepB_MTU | Code=0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
|Ver=6 |Traffic Class | Flow Label | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
|payload length |Next Hdr | Hop Limit | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| src-ipv6 = R1_IPv6 | IPv6
| | Header
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| dest-ipv6 = VtepA_IPv6 | |
| | |
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| ~ Extension Headers ~ (payload type is UDP) | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Source UDP Port (ephemeral) | Dest UDP Port = 4789 (Vxlan) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+8 bytes
| Length | Checksum | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
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| | | | | | | | | Reserved | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+8 bytes
|Vxlan Network identifier (VNI) | Reserved | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Inner Packet Dest-Mac = VtepB_MAC | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | Inner Packet Src-Mac = | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+eth hdr
| VtepA_MAC |14 byte
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Inner Vlan if present |Ethtype = 0X0800 (IPv4) | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
|Ver=6 |Traffic Class | Flow Label | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
|payload length |Next Hdr | Hop Limit | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| src-ipv6 = VtepA_IPv6 |Inner
| | Ipv6
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| dest-ipv6 = H1_IPv6 | |
| | |
| | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| ~ Extension and Transport Headers, Application Data ~ | varies
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
Figure 14. ICMPv6 PDU generated by Intermediate Hop, R1 in Vxlan Network
R1 sends an icmpv6 error "Packet Too Big" directed towards VtepA.
The icmpv6 PDU is shown in Figure 14. VtepA receives the packet with
this icmpv6 PDU and relays it to H1 without any translation as H1 is
connected to VtepA over ipv6 network. All other references about
original packet to be include in the icmpv6 PDU can be taken as it is
from Section 4.1.2.
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0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Dest-Mac = H1_MAC | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | Inner Packet Src-Mac = | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+eth hdr
| VtepA_MAC |14 byte
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Inner Vlan if present |Ethtype = 0X86dd (IPv6) | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
|Ver=6 |Traffic Class | Flow Label | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
|payload length |Next Hdr | Hop Limit | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| src-ipv6 = VtepA_IPv6 |IPv6
| | Header
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| dest-ipv6 = H1_IPv6 | |
| | |
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| ~ Extension Headers ~ (payload type is ICMPV6) | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Type=2 | Code=0 | Checksum | ICMPv6
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type=2
| Next Hop Mtu = R1_VtepB_MTU | Code=0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
|Ver=6 |Traffic Class | Flow Label | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
|payload length |Next Hdr | Hop Limit | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| src-ipv6 = H1_IPv6 |Orig
| |IPv6
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| dest-ipv6 = H2_IPv6 | |
| | |
| | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| ~ Extension and Transport Headers and Applcation data ~ | varies
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
Figure 15. ICMPv6 error Complete Packet sent to H1 by VtepA
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4.1.3.4. Both End-Point and Underlay are provisioned with IPv4
Topology is mentioned in figure 16, with minor changes along with the
legend, figure 17, provides the icmp PDU encap generated by R1.
H1_IPv4 and H2_IPv4 are in different ipv4 subnets.
+----------+ +----------+
| H1 | | H2 |
| | | |
|(H1_IPv4) | |(H2_IPv4) |
+----------+ +----------+
| |
| |
+------------+ +----------+ +------------+
|(VtepA_IPv4)| | | |(VtepB_IPv4)|
| VtepA | | R1 | | VtepB |
|(VtepA_IPv4)|---| (R1_IPv4)|---|(VtepB_IPv4)|
+------------+ +----------+ +------------+
Figure 16. L3 Overlay
LEGEND:
MAC address : <Node_name>_MAC
IPv4 address: <Node_name>_IPv4
<Node_name> : node names in the above topology are
H1, VtepA, R1, VtepB, H2.
VtepA, VtepB: Vxlan gateways to core network
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0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Type=3 | Code=4 | Checksum | ICMP
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type=3
| unused | Length | Next Hop Mtu = R1_VtepB_MTU | Code=4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Ver=4|IHL=5 | TOS | Total length | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Id |Flags| Fragment Offset | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| TTL | Protocol=UDP | Header Checksum | IPv4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Header
| src-ip : VtepA_IPv4 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| dest-ip : H1_IPv4 | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Source UDP Port (ephemeral) | Dest UDP Port = 4789 (Vxlan) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+8 bytes
| Length | Checksum | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| | | | | | | | | Reserved | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+8 bytes
|Vxlan Network identifier (VNI) | Reserved | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Inner Packet Dest-Mac = VtepB_MAC | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | Inner Packet Src-Mac = |inner
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+packet
| VtepA_MAC |eth hdr
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Inner Vlan if present |Ethtype = 0X0800 (IPv4) | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Ver=4|IHL=5 | TOS | Total length | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Id |Flags| Fragment Offset | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| TTL | Protocol | Header Checksum | IPv4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ hdr
| src-ip : H1_IPv4 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| dest-ip : H2_IPv4 | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| ~ Optional and Transport Header and Application Payload ~ |varies
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
Figure 17. ICMP PDU generated by R1 towards VtepA
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R1 sends an icmp error directed towards VtepA. The icmp PDU is shown
in figure 17. VtepA receives the packet with this icmp PDU and
relays it to H1 over ipv4 network. Figure 16, displays the packet
sent by VtepA to H1. All other references can be taken as it is from
Section 4.1.2.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Dest-Mac = H1_MAC | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | Src-Mac = | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ eth
| VtepA_MAC |header
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Inner Vlan if present |Ethtype = 0X0800 (IPv4) | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Ver=4|IHL=5 | TOS | Total length | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Id |Flags| Fragment Offset | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| TTL | Protocol=1 | Header Checksum |IPv4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Header
| src-ip : VtepA_IPv4 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| dest-ip : H1_IPv4 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Optional Header | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Type=3 | Code=4 | Checksum | ICMP
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type=3
| unused | Length | Next Hop Mtu = R1_VtepB_MTU | Code=4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Ver=4|IHL=5 | TOS | Total length | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Id |Flags| Fragment Offset | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| TTL | Protocol | Header Checksum |Orig
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+IPv4
| src-ip : H1_IPv4 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| dest-ip : H2_IPv4 | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
|~ Optional and Transport Header and Application Payload ~ | varies
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
Figure 18. Complete ICMP error Packet sent to H1 by VtepA
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5. Multicast and Anycast Considerations
Multicast solution is similar to one proposed in [RFC1981]. This
SHOULD be applied at Vtep for cases of unknown unicast destinations.
There are no anycast considerations in this document, as the solution
is based upon nodes deriving mtu values from the underlay network
which should either have unicast or multicast reachability between
them.
6. Ecmp Considerations
Ecmp considerations are driven by the packet sent by the end host
application and the way it's leveraged.
To ensure PMTUD is agnostic to ecmp paths in a Vxlan network, there
are few more consideration. In Vxlan Gateway (can be ToR device),
the route look-up is done based on attributes carried in packet
generated by end point host. The packet generated can potentially be
from a tcp based end host application (although should not be
generalized).
Where as, for an intermediate node, (lets say, Spine node in Clos
topology) in core network the look ups are based on Outer Encap (Vtep
ip addresses and and UDP Header).
On another note, for an L2 gateway case, wherein Vxlan gateway (Vtep
Node) bridges (and not routes) host packets destined to same subnet
destination, MTU calculation SHOULD come into play only in the Spine
devices.
7. Security Considerations
This document inherits all the security considerations discussed in
[RFC1981] and [RFC1191].
8. IANA Considerations
TBD
9. Acknowledgements
Thanks to Vengada Prasad Govindan, Deepak Kumar, Matthew Bocci and
Rohit Mendiratta for providing the inputs.
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10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
10.2. Informative References
[I-D.draft-gross-geneve]
Gross, J., Sridhar, T., Garg, P., Wright, C., Ganga, G.,
Agarwal, P., Duda, C., Dutt, D., and J. Hudson, "Geneve:
Generic Network Virtualization Encapsulation", draft-
gross-geneve-02 (work in progress), Oct 2015.
[I-D.draft-ietf-nvo3-gue]
Herbert, T., Yong, L., and O. Zia, "Generic Protocol
Extension for VXLAN", draft-ietf-nvo3-gue-03 (work in
progress), Mar 2015.
[I-D.draft-ietf-nvo3-vxlan-gpe]
Quinn, P., Manur, R., Kreeger, L., Lewis, D., Maino, F.,
Smith, M., Agarwal, P., Yong, L., Xu, X., Elzur, U., and
D. Melman, "Generic Protocol Extension for VXLAN", draft-
ietf-nvo3-vxlan-gpe-02 (work in progress), May 2015.
[I-D.nordmark-nvo3-transcending-traceroute]
Nordmark, E., Appanna, C., and A. Lo, "Layer-Transcending
Traceroute for Overlay Networks like VXLAN", draft-
nordmark-nvo3-transcending-traceroute-02 (work in
progress), March 2015.
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
November 1990.
[RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery
for IP version 6", RFC 1981, August 1996.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control
Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006.
[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
Discovery", RFC 4821, March 2007.
[RFC4884] Bonica, R., Gan, D., Tappan, D., and C. Pignataro,
"Extended ICMP to Support Multi-Part Messages", RFC 4884,
April 2007.
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[RFC7348] Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
eXtensible Local Area Network (VXLAN): A Framework for
Overlaying Virtualized Layer 2 Networks over Layer 3
Networks", RFC 7348, August 2014.
[RFC7637] Yang, S. and M. Garg, "Network Virtualization Using
Generic Routing Encapsulation", RFC 7637, Sep 2015.
Authors' Addresses
Saumya Dikshit
Cisco Systems
Cessna Business Park
Bangalore, Karnataka 560 087
India
Email: sadikshi@cisco.com
A Sujeet Nayak
Cisco Systems
Cessna Business Park
Bangalore, Karnataka 560 087
India
Email: sua@cisco.com
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