Carrying Virtual Transport Network
Identifier in IPv6 Extension HeaderHuawei TechnologiesHuawei Campus, No. 156 Beiqing RoadBeijing100095Chinajie.dong@huawei.comHuawei TechnologiesHuawei Campus, No. 156 Beiqing RoadBeijing100095Chinalizhenbin@huawei.comChina TelecomChina Telecom Beijing Information Science & Technology,
BeiqijiaBeijing102209Chinaxiechf@chinatelecom.cnChina TelecomChina Telecom Beijing Information Science & Technology,
BeiqijiaBeijing102209Chinamachh@chinatelecom.cnA Virtual Transport Network (VTN) is a virtual network which has a
customized network topology and a set of dedicated or shared network
resources allocated from the network infrastructure. A VTN can be used
as the underlay for one or a group of VPNs to provide enhanced VPN
(VPN+) services. In packet forwarding, some fields in data packet needs
to be used to identify the VTN the packet belongs to, so that the
VTN-specific processing can be performed.This document proposes a new option type to carry VTN ID in an IPv6
extension headers to identify the Virtual Transport Network (VTN) the
packet belongs to. The procedure for processing of the VTN option is
also specified.Virtual Private Networks (VPNs) provide different groups of users
with logically isolated connectivity over a common shared network
infrastructure. With the introduction of 5G, new service types may
require connectivity services with advanced characteristics comparing to
traditional VPNs, such as strict isolation from other services or
guaranteed performance. These services are refered to as "enhanced VPNs"
(VPN+). describes a
framework and candidate component technologies for providing VPN+
services.The enhanced properties of VPN+ require tighter coordination and
integration between the underlay network resources and the overlay
network. VPN+ service can be built on a Virtual Transport Network (VTN)
which has a customized network topology and a set of dedicated or shared
network resources allocated from the underlay network. The overlay VPN
together with the corresponding VTN in the underlay provide the VPN+
service. In the network, traffic of different VPN+ services need to be
processed separately based on the topology and the network resources
associated with the corresponding VTN. describes
the scalability considerations for VPN+, one of which is to improve the
data plane scalability through the introduction of a dedicated
identifier in data packets that is used to identify the VTN the packets
belong to, so that VTN-specific packet processing can be performed. This
is called Resource Independent (RI) VTN.This document proposes a mechanism to carry the VTN ID in an IPv6
extension header of a packet, so that the
packet will be processed by network nodes using the network resources
allocated to the corresponding VTN. The procedure for processing the VTN
ID is also specified. This provides a scalable solution for enhanced VPN
data plane, so that it may be used to support a large number of VTNs in
an IPv6 network.The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP14
RFC 2119RFC
8174 when, and only when, they appear in all capitals, as shown
here.A new option type "VTN" is defined to carry the Virtual Transport
Network Identifier (VTN ID) in an IPv6 packet header. Its format is
shown as below:Option Type: 8-bit identifier of the type of option. The type of VTN
option is to be assigned by IANA. The highest-order bits of the type
field are defined as below:BB 00 The highest-order 2 bits are set to 00 to indicate that a
node which does not recognize this type will skip over it and
continue processing the header.C 0 The third highest-order bit are set to 0 to indicate this
option does not change en route.Opt Data Len: 8-bit unsigned integer indicates the length of the
option Data field of this option, in octets. The value of Opt Data Len
of VTN option SHOULD be set to 4.Option Data: 4-octet identifier which uniquely identifies a VTN.Editor's note: The length of the VTN ID is defined as 4-octet for the
matching with the 4-octet Single Network Slice Selection Assistance
Information (S-NSSAI) defined in 3GPP .As the VTN option needs to be processed by each node along the path
for VTN-specific forwarding, it SHOULD be carried in IPv6 Hop-by-Hop
options header when the Hop-by-Hop options header can be processed in
forwarding plane by all the nodes along the path.When an ingress node of an IPv6 domain receives a packet, according
to traffic classification or mapping policy, the packet is steered
into one of the VTNs in the network, then packet SHOULD be
encapsulated in an outer IPv6 header, and the VTN-ID of the VTN which
the packet is mapped to SHOULD be carried in the Hop-by-Hop options
header associated with the outer IPv6 header.On receipt of a packet with the VTN option, each network node which
can parse the VTN option SHOULD use the VTN ID to identify the VTN the
packet belongs to. This means the forwarding behavior is based on both
the destination IP address and the VTN option. The destination IP
address is used for the lookup of the next-hop node, and VTN-ID can be
used to determine the set of network resources reserved for processing
and sending the packet to the next-hop node. The egress node of the
IPv6 domain SHOULD decapsulate the outer IPv6 header.There can be different implementations for reserving local network
resources to the VTNs. For example, on one interface, a subset of
forwarding plane resource allocated to a particular VTN can be
considered as a virtual sub-interface with dedicated bandwidth and
other associated resources. In packet forwarding, the IPv6 destination
address of the received packet is used to identify the next-hop and
the outgoing interface, and the VTN ID is used to further identify the
virtual sub-interface which is associated with the VTN on the outgoing
interface.Routers which do not support Hop-by-Hop options header SHOULD
ignore the Hop-by-Hop options header and forward the packet only based
on the destination IP address. Routers which support Hop-by-Hop
Options header, but do not support the VTN option SHOULD ignore the
Hop-by-Hop option and continue to forward the packet only based on the
destination IP address.As described in , nodes may be configured to
ignore the Hop-by-Hop Options header, and in some implementations a
packet containing a Hop-by-Hop Options header may be dropped or assigned
to a slow processing path. This needs to be taken into consideration
when VTN option is introduced to a network. The operator needs to make
sure that all the network nodes in a VTN can either process Hop-by-Hop
Options header in packet forwarding, or ignore the Hop-by-Hop Option
header. In other word, packets steered into a VTN MUST NOT be dropped
due to the existence of the Hop-by-Hop Options header. It is RECOMMENDED
to configure all the nodes in a VTN to process the Hop-by-Hop Options
header if there is a nob for this.This document requests IANA to assign a new option type from
"Destination Options and Hop-by-Hop Options" registry.TBDThe authors would like to thank Juhua Xu and James Guichard for their
review and valuable comments.3GPP TS23.501