| Internet-Draft | Computing Segment for Service Routing | April 2023 |
| Zhou, et al. | Expires 22 October 2023 | [Page] |
Since services provisioning requires delicate coordination among the client, network and cloud, this draft defines a new Segment to provide service routing and addressing functions by leveraging SRv6 Segment programming capabilities. With Computing Segments proposed, the network gains its capability to identify and process a SAN header in need and a complete service routing procedure can be achieved.¶
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In order to deliver responsive services to clients, computing resources continuously migrate and spread from central sites to edge nodes. As shown in Figure 1, multiple instances located distributedly in different resource pools are capable of providing services. Compared with applying traditional IP routing protocols, a fine-grained service routing policy is capable of achieving optimal and efficient invocation of both computing power and the network.¶
+-------------+ +---------+
+-+Load Balancer+-+Service 1|
| +-------------+ +---------+
|
+------+ +----------+ +---------+ | +-------------+ +---------+
|Client+---+Ingress PE+---+Egress PE+-+-+Load Balancer+-+Service 2|
+------+ +----------+ +---------+ | +-------------+ +---------+
|
| +-------------+ |---------+
+-+Load Balancer+-|Service 3|
+-------------+ +---------+
|<-Client->|<---------Network-------->|<----------Cloud---------->|
In order to implement service routing, the network should be aware of specific services and a service awareness network framework is introduced in [I-D.huang-service-aware-network-framework]. Within the proposed network framework, a service identification is defined as a SAN ID(Service ID) in [I-D.ma-intarea-identification-header-of-san] to represent a globally unique service semantic identification.¶
As mentioned in [I-D.ma-intarea-encapsulation-of-san-header], a SAN ID is encapsulated in a SAN header which can be carried as an option in the IPv6 Hop-by-Hop Options Header, Destination Options Header and a type of SRH TLV. Since services provisioning requires delicate coordination among the client, network and cloud and thus simply encapsulating SAN header among packets delivery can hardly satisfy various practical situations:¶
To achieve a SAN header being processed in need in the network domain and to preserve its identifiability along the path from the client to the server, a new Segment to specify and standardize node behaviours is urgently required.¶
As shown in Figure 2, a service routing table is designed to establish a mapping relationship between the SAN ID and the conventional IP routing table.¶
+-------+
| I P |
SAN ID <-------------> |Routing|
| | Table |
| +-------+
v
+-------+
|Service|
|Routing|
| Table |
+-------+
+--------+ +-----------+ +----------+ +-----+
| Client +--------+Ingress PE+----------+Egress PE+--------+ L B |
+--------+ +-----------+ +----------+ +-----+
A service routing table can be published from a control and management system to the network domain within a centralized control plane while it can also be calculated and generated by the Ingress PE itself under a distributed control plane.¶
With considerations of path metrics, computing status and service SLA requirements, a specific service routing table is introduced, including mutiple attributes, SAN ID and outer gateway for instance. Afterwards, a corresponding IP routing table should be indexed which further determines the next hop or an SRv6 policy.¶
In order to describe and standardize the mentioned behaviours, a new Computing Segment is proposed. With Computing Segments, multiple nodes in the network domain can be informed to identify and resolve SAN header in need and to implement a referred forwarding behaviour through the complete procedure.¶
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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
This draft introduces a new SRv6 Segment, namely Computing Segment, aiming to describe the behaviour of querying service routing table and corresponding packet forwarding.¶
Computing Segment is the identifier of packets in which a corresponding SAN header should be identified and further being forwarded via the matched service routing table entity, indicating the following operations:¶
In the case of SRv6, a new behavior End.C for Computing Segment is defined. Behaviours of End.C are described in the following sections.¶
When an IPv6 node (N) receives an IPv6 packet whose destination address matches a local IPv6 address instantiated as a SID (S), and S is a Computing SID, N does:¶
(1) If the traffic is steered into a tunnel, an SRv6 policy for instance:¶
S01. If (IPv6 Hop Limit <= 1) {
S02. Send an ICMP Time Exceeded message to the Source Address
with Code 0 (Hop limit exceeded in transit),
interrupt packet processing, and discard the packet.
S03. }
S04. Decrement IPv6 Hop Limit by 1
S05. Resolve the SAN ID encapsulated in the DOH
S06. Maintain the SAN Header in the DOH
S07. Query the service routing table indexed by SAN ID to determine
an outer gateway and an according SRv6 policy
S08. If an SRH is carried in the IPv6 header {
S09. If (Segments Left == 0) {
S10. Stop processing the SRH, and proceed to process the next
header in the packet, whose type is identified by
the Next Header field in the routing header.
S11. }
S12. max_LE = (Hdr Ext Len / 2) - 1
S13. If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) {
S14. Send an ICMP Parameter Problem to the Source Address
with Code 0 (Erroneous header field encountered)
and Pointer set to the Segments Left field,
interrupt packet processing, and discard the packet.
S15. }
S16. Decrement Segments Left by 1
S17. Update IPv6 DA with Segment List[Segments Left]
S18. }
S19. else {
S20. Update IPv6 DA with the queried gateway
S21. }
S22. Push a new IPv6 header with its own SRH containing the list of
segments of the SRv6 policy
S23. Set the outer IPv6 SA to itself
S24. Set the outer IPv6 DA to the first SID of the SRv6 policy
S25. Set the outer Payload Length, Traffic Class, Flow Label and
Next Header fields
S26. Submit the packet to the egress IPv6 FIB lookup for transmission
to the new destination
(2) If the traffic is steered in a BE manner:¶
The line S07 and lines from S22 to S24 are replaced by the following:¶
S07. Query the service routing table indexed by SAN ID to determine
an outer gateway
S22. Push a new IPv6 header
S23. Set the outer IPv6 SA to itself
S24. Set the outer IPv6 DA to the queried outer gateway
When an IPv6 node (N) receives an IPv6 packet whose destination address matches a local IPv6 address instantiated as a SID (S), and S is a Computing SID, N does:¶
(1) If the traffic is steered into a tunnel, an SRv6 policy for instance:¶
S01. If (IPv6 Hop Limit <= 1) {
S02. Send an ICMP Time Exceeded message to the Source Address
with Code 0 (Hop limit exceeded in transit),
interrupt packet processing, and discard the packet.
S03. }
S04. Decrement IPv6 Hop Limit by 1
S05. Resolve the SAN ID encapsulated in the HBH
S06. Maintain the SAN Header in the HBH
S07. Query the service routing table indexed by SAN ID to determine
an outer gateway and an according SRv6 policy
S08. If an SRH is carried in the IPv6 header {
S09. If (Segments Left == 0) {
S10. Stop processing the SRH, and proceed to process the next
header in the packet, whose type is identified by
the Next Header field in the routing header.
S11. }
S12. max_LE = (Hdr Ext Len / 2) - 1
S13. If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) {
S14. Send an ICMP Parameter Problem to the Source Address
with Code 0 (Erroneous header field encountered)
and Pointer set to the Segments Left field,
interrupt packet processing, and discard the packet.
S15. }
S16. Decrement Segments Left by 1
S17. Update IPv6 DA with Segment List[Segments Left]
S18. }
S19. else {
S20. Update IPv6 DA with the queried gateway
S21. }
S22. Push a new IPv6 header with its own SRH containing the list of
segments of the SRv6 policy
S23. Set the outer IPv6 SA to itself
S24. Set the outer IPv6 DA to the first SID of the SRv6 policy
S25. Set the outer Payload Length, Traffic Class, Flow Label and
Next Header fields
S26. Submit the packet to the egress IPv6 FIB lookup for transmission
to the new destination
(2) If the traffic is steered in a BE manner:¶
The line S07 and lines from S22 to S24 are replaced by the following:¶
S07. Query the service routing table indexed by SAN ID to determine
an outer gateway
S22. Push a new IPv6 header
S23. Set the outer IPv6 SA to itself
S24. Set the outer IPv6 DA to the queried outer gateway
When an IPv6 node (N) receives an IPv6 packet whose destination address matches a local IPv6 address instantiated as a SID (S), and S is a Computing SID, N does:¶
(1) If the traffic is steered into a tunnel, an SRv6 policy for instance:¶
S01. When an SRH is processed {
S02. If (Segments Left == 0) {
S03. Stop processing the SRH, and proceed to process the next
header in the packet, whose type is identified by
the Next Header field in the routing header.
S04. }
S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address
with Code 0 (Hop limit exceeded in transit),
interrupt packet processing, and discard the packet.
S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1
S09. If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) {
S10. Send an ICMP Parameter Problem to the Source Address
with Code 0 (Erroneous header field encountered)
and Pointer set to the Segments Left field,
interrupt packet processing, and discard the packet.
S11. }
S12. Decrement IPv6 Hop Limit by 1
S13. Decrement Segments Left by 1
S14. Update IPv6 DA with Segment List[Segments Left]
S15. Resolve the SAN ID encapsulated in the HBH, DOH or a type of
SRH TLV
S16. Maintain the SAN Header in the HBH, DOH or a type of SRH TLV
S17. Query the service routing table indexed by SAN ID to determine
an outer gateway and an according SRv6 policy
S18. Push a new IPv6 header with its own SRH containing the list of
segments of the SRv6 policy
S19. Set the outer IPv6 SA to itself
S20. Set the outer IPv6 DA to the first SID of the SRv6 policy
S21. Set the outer Payload Length, Traffic Class, Flow Label and
Next Header fields
S22. Submit the packet to the egress IPv6 FIB lookup for transmission
to the new destination
S23. }
(2) If the traffic is steered in a BE manner:¶
The lines from S17 to S20 are replaced by the following:¶
S17. Query the service routing table indexed by SAN ID to determine
an outer gateway
S18. Push a new IPv6 header
S19. Set the outer IPv6 SA to itself
S20. Set the outer IPv6 DA to the queried outer gateway
When a SAN header is carried as an option in the DOH, a typical service routing procedure is shown in Figure 9.¶
+--------+ +-----------+ +----------+ +-----+
| Client +---------+Ingress PE+--------+Egress PE+---------+ L B |
+--------+ +-----------+ +----------+ +-----+
Inner IPv6 Packet:
+-----------+ +-----------+ +-----------+
| SIP | | SIP | | SIP |
+-----------+ +-----------+ +-----------+
|END.C(SID1)| |END.C(SID2)| | DIP |
+-----------+ +-----------+ +-----------+
| DOH | | DOH | | DOH |
+-----------+ +-----------+ +-----------+
| PAYLOAD | | PAYLOAD | | PAYLOAD |
+-----------+ +-----------+ +-----------+
DOH:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Opt Length |Opt Data Length|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SAN Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
Service Routing Table: v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SAN ID | Gateway | Interface |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID 1 | Egress 1 | Policy 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID 2 | Egress 2 | Policy 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ...... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Suppose the Endpoint behaviour of END.C is configured at Ingress PE and Egress PE, namely SID 1 and SID 2 respectively. SID1 and SID2 are advertised in the network domain by IGP. The client registers with the management and operation system to acquire a SAN ID and encapsulates it in the packet. The initial destination is END.C (SID 1) which may be configured in a static routing manner. The service addressing procedure from the client to the cloud is described below:¶
|<-Client->|<-------------------Network----------------->|<-Cloud->|
+------+ +----------+ +---------+ +-----+
|Client+-----+Ingress PE+-------------------+Egress PE+-----+ L B |
+------+ +----------+ | +---------+ +-----+
BE: v TE:
+-----------+ +-----------+
| IIP | | IIP |
+-----------+ +-----------+
| SID | | SID |
+-----------+ +-----------+
| SIP | | SRH |
+-----------+ +-----------+
|END.C(SID2)| | SIP |
+-----------+ +-----------+
| DOH | |END.C(SID2)|
+-----------+ +-----------+
| PAYLOAD | | DOH |
+-----------+ +-----------+
| PAYLOAD |
+-----------+
As shown in Figure 10, between Ingress PE and Egress PE, an outer header including SRH should be encapsulated when the traffic follows a specific SRv6 TE policy. Otherwise, a normal IPv6 header should be encapsulated under a BE condition.¶
Security has always been an indispensable and significant consideration for design and innovation in the fields of communication and services provisioning. A Computing Segment as END.C defined in this draft may be given security semantics and according behaviours, including encryption and decryption, etc. Security considerations may be studied in the future work.¶
TBA.¶
This document requires registration of End.C behavior in "SRv6 Endpoint Behaviors" sub-registry of "Segment Routing Parameters" registry.¶