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End.AM SID —Applies to the SRv6 service chain masquerading scenario. For more information about End.AM SIDs, see "Configuring SRv6 service chains."
Use IGP to advertise SRv6 SIDs for an SR node. The other SR nodes will generate route entries of that SR node based on the advertised information.
SRv6 SID flavors
Use SRv6 SID flavors to change the forwarding behaviors of SRv6 SIDs in order to meet multiple service requirements. The following SRv6 SID flavors are supported:
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Penultimate Segment POP of the SRH (PSP) —The penultimate SRv6 node removes the
SRH to reduce the workload of the end SRv6 node and improve the forwarding efficiency. The end SRv6 node does not read the SRH, and it only looks up the local SID table for the destination IPv6 address of packets to forward the packets.
•
NO PSP —The penultimate SRv6 node does not remove the SRH.
Local SID forwarding table
An SRv6-enabled node maintains a local SID forwarding table that records the SRv6 SIDs generated on the local node. The local SID forwarding table has the following functions:
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Stores local generated SRv6 SID forwarding information.
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Stores SRv6 SID operation types.
Segment List
A Segment List is an ordered list of SIDs, which is also referred to as a Segment Identifier (SID) list in this document. The SR nodes forward packets based on the SIDs in the order that they are arranged in the SID list.
SRv6 tunnel
An SRv6 tunnel is a virtual point-to-point connection established between the SRv6 ingress node and egress node. IPv6 packets are encapsulated at the ingress node and de-encapsulated at the egress node.
SRv6 packet format
An outer IPv6 header and a Segment Routing Header (SRH) are added to the original Layer 3 data packet to form an SRv6 packet.
As shown in Figure 34 , the value for the
Next Header field is 43 in the outer IPv6 header, which indicates that the header next to the IPv6 header is a routing extension header. The value for the
Routing Type field in the routing extension header is 4, which indicates that the routing extension header is an SRH. The SRH header contains the following fields:
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8-bit Next Header —Identifies the type of the header next to the SRH.
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8-bit Hdr Ext Len —Length of the SRH header in 8-octet units, not including the first 8 octets.
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8-bit Routing Type —The value for this field is 4, which represents SRH.
•
8-bit Segments Left —Contains the index of the next segment to inspect in the Segment List.
The Segments Left field is set to n -1 where n is the number of segments in the Segment List.
Segments Left is decremented at each segment.
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8-bit Last Entry —Contains the index of the first SID in the path used to forward the packet.
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8-bit Flags —Contains flags.
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16-bit Tag —Tags a packet as part of a class or group of packets, for example, packets sharing the same set of properties.
•
Segment List —Contains 128-bit IPv6 addresses representing the ordered segments. The
Segment List is encoded starting from the last segment of the path. The first element of the segment list (Segment List [0]) contains the last segment of the path, the second element
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