The BGP service control plane required extensions are specified in draft-ietf-bess-srv6-services. BGP requires some changes in the IPv6, VPN-IPv4, VPN-IPv6 and EVPN family routes so that the egress PE can signal the following End programming behaviors to the ingress PE:
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Layer-3 SRv6 Service SIDs
- End.DT4
- a VPRN (or GRT) route-table lookup; signaled by VPN-IPv4 or EVPN-IFL IPv4 prefix routes (also by IPv4)
- End.DT6
- a VPRN (or GRT) route-table IPv6 lookup; signaled by VPN-IPv6 or EVPN-IFL IPv6 prefix routes (also by IPv6)
- End.DT46
- a VPRN route-table lookup for IPv4 or IPv6 prefixes; signaled by VPN-IPv4/6 or EVPN-IFL IPv4/6 prefix routes
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Layer-2 SRv6 Service SIDs
- End.DX2
- Layer 2 decapsulation and cross-connect to an Epipe egress SAP; signaled by A-D per EVI routes.
Note: End.DX2 is not supported in Release 21.5.
Figure 1 shows an example for the End.DX2 behavior for EVPN-VPWS services.
The ingress and egress PEs behave as follows:
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The egress PE (PE6) advertises an A-D per EVI route with the SRv6 Service SID that identifies the End.DX2 behavior. The service SID includes the configured locator in the Epipe (A6::), as well as the allocated function (E9), that identifies the Epipe at the egress PE.
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The ingress PE (PE1) imports the A-D per EVI route and creates an EVPN destination in the corresponding Epipe to A6::E9.
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When PE1 receives frames at the access SAP, it encapsulates the frames into an SRv6 packet, using the configured IP SA. The IP DA is the EVPN destination SID.
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Shortest path forwarding is considered in the example shown in Figure 1, and therefore the EVPN destination SID is encoded in the IP DA. If TI-LFA is required, PE1 modifies the encapsulation to include an SRH and additional SIDs.
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When the SRv6 packet arrives at PE6, the SID encoded in the IP DA identifies the packet for termination on PE6, and the Epipe for decapsulation and forwarding.
Similar procedures are followed for the other required services.