| LSR Working Group | Yao. Liu |
| Internet-Draft | Zheng. Zhang |
| Intended status: Standards Track | ZTE Corporation |
| Expires: August 27, 2020 | February 24, 2020 |
IGP Extensions for Segment Routing Service Segment
draft-lz-lsr-igp-sr-service-segments-01
This document defines extensions to the link-state routing protocols (IS-IS and OSPF) in order to carry service segment information via IGP.
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Segments are introduced in the SR architecture [RFC8402]. Segment Routing (SR) allows for a flexible definition of end-to-end paths by encoding paths as sequences of topological sub-paths, called "segments".
Service Function Chaining (SFC) [RFC7665] provides support for the creation of composite services that consist of an ordered set of Service Functions (SF) that are to be applied to packets and/or frames selected as a result of classification.
[I-D.ietf-spring-sr-service-programming] describes how a service can be associated with a SID and how to achieve service funtion chaining in SR-enabled MPLS and IPv6 networks. It also defines SR-aware and SR-unaware services. For a SR-unaware service ,there has to be a SR proxy handling the SR processing on behalf of the service .
[I-D.dawra-idr-bgp-ls-sr-service-segments] propose extensions to BGP-LS for Service Chaining to distribute the service segment information to SR Controller.
SR-C
|
|
A----1----2----3----4----5----B
| |
| |
S1 S2 proxy----S2
Figure 1: Figure 1:Network with Services
The network topology is shown in figure 1.
Node 1-5 are nodes capital of segment routing. A and B are two end hosts. S1 is an SR-aware Service. S2 is an SR-unaware Service.
SR Controller (SR-C) is connected to node 1, but may be attached to any node 1-5 in the network.
SR-C is capable of receiving BGP-LS updates to discover topology, and calculating constrained paths between 1 and 5.
If node 1 gets the service segment information, it can use the BGP-LS extensions [I-D.ietf-spring-sr-service-programming] to advertise it to the SR-C, but how can node 1 get it is a question.but node 1 must get the service segment information from other nodes at first.
This document proposes extensions for IGP to advertise service segment information so that there is only one SR node needed per Autonomous System to be connected with the SR-C through BGP-LS to advertise the information to it.
This extension works for both SR-MPLS and SRv6.
After an SFF like node 2 or node 4 get the service segment information, it needs to advertise the information to other SR nodes in the domain through IGP.
How can SFFs like node 2 and node 4 get the service segment information from S1 and S2 proxy will be discussed further.
There may be other alternate mechanisms and are outside of scope of this document.
This document introduces new TLVs for SRv6 End SID sub-TLV [I-D.ietf-lsr-isis-srv6-extensions] and SID/Label sub-TLV [RFC8666] for SR-MPLS to associate the Service SID Value with Service-related Information.
One of the new TLVs is Service Chaining (SC) TLV, the TLV is defined as follows :
+---------------------------------------+
| Type (1 octet) |
+---------------------------------------+
| Length (1 octet) |
+---------------------------------------+
| Service Type(ST) (2 octet) |
+---------------------------------------+
| Flags (1 octet) |
+---------------------------------------+
| Traffic Type(1 octet) |
+---------------------------------------+
| RESERVED (2 octet) |
+---------------------------------------+
Figure 2:Service Chaining (SC) TLV
where:
Type,Length,Flags,Traffic Type and RESERVED are the same as the SC TLV defined in [I-D.dawra-idr-bgp-ls-sr-service-segments] chapter 2.
Service Type: 16-bits field.The right most 12 bits categorize the Service: (such as "Firewall", "Classifier" etc.).
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | P FLAG| Service info | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3:Service Type(ST) Field
The first 4 bits are P FLAG which is used to indicate the SR proxy type with the following values:
0000:SR-aware function.
0001:Static proxy.
0010:Dynamic proxy.
0011:Masquerading proxy.
0100:Shared memory proxy.
Other values are reserved for new types of proxy.
The P FLAG is mainly defined for SR-MPLS.
In SRv6,although most proxy types can be represented by the END functions[I-D.ietf-spring-sr-service-programming], there may be situations that the new type of proxy cannot be associated with the network programming function, or the SR proxy node does not support standard network programming, so the P flag is still useful.
In the IS-IS notification message, when both SR proxy END function and P FLAG exist, the proxy type represented by END function shall prevail.
Another Optional Opaque Metadata(OM) TLV is defined in figure 4. The definition and structure are the same as the OM TLV defined in [I-D.dawra-idr-bgp-ls-sr-service-segments] chapter 2.
+---------------------------------------+
| Type (1 octet) |
+---------------------------------------+
| Length (1 octet) |
+---------------------------------------+
| Opaque Type (2 octet) |
+---------------------------------------+
| Flags (1 octet) |
+---------------------------------------+
| Value (variable) |
+---------------------------------------+
Figure 4:Opaque Metadata(OM) TLV
This document introduces new TLVs for SRv6 End SID sub-TLV [I-D.li-ospf-ospfv3-srv6-extensions] and SID/Label sub-TLV [RFC8665]for SR-MPLS to associate the Service SID Value with Service-related Information.
One of the new TLVs is Service Chaining (SC) TLV,
+---------------------------------------+
| Type (2 octet) |
+---------------------------------------+
| Length (2 octet) |
+---------------------------------------+
| Service Type(ST) (2 octet) |
+---------------------------------------+
| Flags (1 octet) |
+---------------------------------------+
| Traffic Type(1 octet) |
+---------------------------------------+
| RESERVED (2 octet) |
+---------------------------------------+
Figure 5:Service Chaining (SC) TLV
where:
Type,Length,Flags,Traffic Type and RESERVED are the same as the SC TLV defined in [I-D.dawra-idr-bgp-ls-sr-service-segments] chapter 2.
The definition and use principle of the Service Type field is the same as that defined in the IS-IS extension above.
Another Optional Opaque Metadata(OM) TLV is defined in figure 6. The definition and structure are the same as the OM TLV defined in [I-D.dawra-idr-bgp-ls-sr-service-segments] chapter 2.
+---------------------------------------+
| Type (2 octet) |
+---------------------------------------+
| Length (2 octet) |
+---------------------------------------+
| Opaque Type (2 octet) |
+---------------------------------------+
| Flags (1 octet) |
+---------------------------------------+
| Value (variable) |
+---------------------------------------+
Figure 6:Opaque Metadata(OM) TLV
Procedures and protocol extensions defined in this document do not affect the IS-IS and OSPF security model
TBD
| [RFC8402] | Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B., Litkowski, S. and R. Shakir, "Segment Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, July 2018. |