| NVO3 | S. Dikshit |
| Internet-Draft | A. Sujeet Nayak |
| Intended status: Standards Track | Cisco Systems |
| Expires: December 19, 2016 | June 17, 2016 |
PMTUD Over Vxlan
draft-saum-nvo3-pmtud-over-vxlan-03
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.
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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.
The proposal in this document, formulates an integrated approach which falls inline with OAM modelling discussed in NVO3./>.
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].
This section describes the advantages of the proposed solution, considering deployment in a typical data center core network:
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) 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.
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,
The problems are discussed in detail in the following sub-sections.
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 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.
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.
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.
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.
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'.
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 generation of ICMP or ICMPv6 error by intermediate node in underlay network.
+----------------------------------------------------+
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
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: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
VtepA re-writes the mac addresses in 'P1' as part of Vxlan encapsulation. This encapsulation is referred as 'P2' in the document.
Processing at VtepA, in packet path from H1 to H2.
+----------------------------------------------------------+
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
In case the underlay is ipv6 and not ipv4, icmpv6 error is generated.
Processing at R1:
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.
+-----------------------------------------------------------+
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 | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
|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
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):
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.
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)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| 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.
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.
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.
This case is similar to the last leg processing described in Section 4.1.2 and does not needs any more description.
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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| 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.
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
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.
+----------+ +----------+
| 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 | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------ | | | | | | | | | 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.
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
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
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
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
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.
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.
This document inherits all the security considerations discussed in [RFC1981] and [RFC1191].
TBD
Thanks to Vengada Prasad Govindan, Deepak Kumar, Matthew Bocci and Rohit Mendiratta for providing the inputs.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |