Extensions for SRv6 traversing IPv4
networkHuawei TechnologiesHuawei Campus, No. 156 Beiqing Rd.Beijing100095Chinalizhenbin@huawei.comHuawei TechnologiesHuawei Campus, No. 156 Beiqing Rd.Beijing100095Chinac.l@huawei.com
Routing Area
SPRING Working GroupAs the development of cloud computing, increasing services have been
migrated from enterprise sites to clouds, so the connections between
sites and clouds are critical for enterprises.SRv6 provides a sourcing routing mechanism to connect the enterprise
sites and clouds by programming the end-to-end path at the ingress node.
In this scenario, the SRv6 packets may traverse multiple network domains
and some of them may not be SRv6-capable.In order to support SRv6 end-to-end path programming, this document
proposes the mechanism of SRv6 traversing IPv4 network.When segment routing (SR) is deployed on the
IPv6 data plane, it is called SRv6 . For support
of SR, a new routing header called Segment Routing Header (SRH), which
contains a list of SIDs and other information, has been defined in .When deploying SRv6, the SRv6 network may need to interwork with
exiting networks, such as MPLS netwoks and IPv4 networks.With the development of cloud computing, increasing services have
been migrated from enterprises to cloud data centers. Compared with
interconnections between branches and headquarters, new connections
between enterprise sites to cloud data centers and inter-cloud are
added, which bring new requirements and challenges for existing
networks. describes the
requirements and candidate technologies in IPv6-based Cloud-oriented
Networking (CON). In IPv6-based CON, SRv6 can be used to connect
enterprise sites and clouds. In this scenario, an SRv6 packet may be
forwarded traversing IPv4 domains. The Tunnel Segment is defined in to associate a tunnel to a
segment in SRv6 and SR-MPLS, therefore, its dataplane is IPv6 or MPLS.
The document defines the a new types of tunnel segment to associate an
IPv4 tunnel to an SRv6 SID for supporting end-to-end path programming
traversing IPv4 domains. Furthermore, this document also defines the
mechanism of encoding the IPv4 tunnel information in the SRH at the
source node to provide better source routing programming.This document makes use of the terms defined in , and the reader is assumed to be familiar with that
terminology.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 BCP
14 when, and only
when, they appear in all capitals, as shown here.This document defines the following mechanisms for SRv6 traversing
IPv4 networks.This document defines a new End.B4 (End bound to an IPv4 tunnel)
behavior for an SRv6 SID bound to an IPv4 tunnel.End.B4 SID MUST NOT be the last SID in the segment list. When the
node receives a packet with End.B4 SID, the packet is steered into the
bound IPv4 tunnel.When node N receives a packet whose IPv6 DA is S and S is a local
End.B4 SID, the line S15 - S16 from the End processing is replaced by the following:Another option is to carry the IPv4 tunnel information in the SRH.
The IPv4 tunnel information can be encoded in another 128-bit value
following the SID or SRH TLVs.In this revision, this section defines an End.4 (End function with
IPv4 tunnel instantiation) behavior for an SRv6 SID to indicate a
128-bit IPv4 tunnel information is encoded following the SID.An End.4 SID MUST be encoded preceding the IPv4 tunnel information
encapsulation, thus it can not be the last SID in the SID list. In
addition, the IPv6 address is needed to be updated by the next SRv6
SID, therefore the IPv4 tunnel information encapsulation MUST NOT be
the last SID as well.The SRv6 path of crossing IPv4 domain is called IPv4 sub-path. An
IPv4 sub-path is encoded by an END.4 SID and the following IPv4 tunnel
information encapsulation as shown in the following figure.When encoding the end-to-end forwarding path, the ingress encodes
the End.4 SID and related IPv4 tunnel info into the SID list, the
encoding of IPv4 tunnel information is shown in section 3.2.1.When a node processes an End.4 SID, it encapsulates the SRv6 packet
with an IPv4 tunnel header using the information carried by the IPv4
tunnel information, decreases the SL accordingly and then sends the
packet by looking up the IPv4 destination address in the IPv4
header.When node N receives a packet whose IPv6 DA is S and S is a local
End.B4 SID, the line S02 from the End processing is replaced by the following:The lines S13-S16 are replaced by the following pseudo code.An IPv4 Tunnel Information Encapsulation contains 128 bits IPv4
tunnel related information. The format is shown below.The IPv4 tunnel information includes tunnel type, source IPv4
address, destination IPv4 address and tunnel parameters. Different
types of IPv4 tunnels have specific parameters:IPv4 UDP tunnel: the tunnel parameters includes source port
and destination port.IPv4 VXLAN tunnel: the tunnel parameters includes source
port, destination port and VN ID.The detailed encapsulation formats for different types of IPv4
tunnel is out of scope of the document.The IPv4 tunnel information MAY be carried in SRH TLV as
well.A TLV Carrying (TC) Flavor is defined to indicate the SID related
information is carried within the SRH TLV.Therefore, an End.4(TC) SID indicates to read the IPv4 tunnel
information in the SRH TLV.A mechanism of specifying which SRH TLV to be processed by which
SID in the SID list is defined in , and it can
be used for indicating the node to processing IPv4 tunnel
information in SRH TLV. More details will be described in the
future.For easy understanding, this section illustrates how to use End.4 SID
for SRv6 traversing IPv4 networks.Assuming thatA::1:200 is the End.4 SID for traversing an IPv4 domain.192.168.0.1 is the source address of the IPv4 tunnel.192.168.0.2 is the destination address of the IPv4 tunnel.The programmed SRv6 path is shown in Figure 3:When the node processes the End.4 SID A::1:200, it encapsulates a new
IPv4 header for the SRv6 packet, setting source IPv4 address as
192.168.0.1, and destination address as 192.168.0.2, and parameters
accordingly. Also, the inner IPv6 DA is updated by the next SID
following the IPv4 tunnel information. The node looks up the IPv4
destination address and forward the packet.TBDTBD