If the SI value is equal to 0, the device decreases the SL value by 1, resets the SI value to 3, and searches for the G-SID group corresponding to the SL value of the packet. Then, the device calculates the destination address based on the 32-bit G-SID identified by SI value 3.
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If the destination address of the packet is a 32-bit SRv6 SID without the COC flag in the segment list, the device decreases the SL value by 1 and searches for the 128-bit SRv6 SID corresponding to [SL-1]. Then, the device replaces the destination address in the IPv6 header with the SRv6 SID.
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If the destination address of the packet is a 128-bit SRv6 SID without the COC flag in the segment list, the device decreases the SL value by 1 and searches for the 128-bit SRv6 SID corresponding to [SL-1]. Then, the device replaces the destination address in the IPv6 header with the SRv6 SID.
BGP-EPE
IGP for SRv6 cannot advertise SRv6 SIDs across ASs. To advertise SRv6 SIDs across ASs, use
BGP Egress Peer Engineering (BGP-EPE).
BGP-EPE can allocate BGP peer SIDs to inter-AS segments.
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If the device has established BGP LS peer relationship with a network controller, it advertises the peer SIDs to the network controller through extended BGP LS messages. Then, the controller orchestrates the IGP SIDs and BGP peer SIDs to realize optimal inter-AS traffic forwarding.
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If the device has not established BGP LS peer relationship with a network controller, it advertises the peer SIDs to a BGP peer through BGP LS messages. When a device that has established BGP LS peer relationship with a network controller receives the peer SIDs, it advertises the peer SIDs to the network controller through BGP LS messages.
BGP-EPE supports automatic peer SID allocation and static peer SID allocation. As shown in Figure
40,
BGP-EPE can allocate the following peer SIDs:
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PeerNode SID —Identifies a peer node. BGP-EPE allocates a PeerNode SID to each BGP session. If the device establishes EBGP peer relationship with a peer through a loopback interface, it might have multiple physical links to reach the peer. In this case, the PeerNode SID for this peer is associated with multiple output interfaces. Traffic destined for this peer based on the PeerNode SID will be distributed among these output interfaces.
•
PeerAdj SID —Identifies an adjacency link that can reach a peer node. If the device establishes
EBGP peer relationship with a peer through a loopback interface, it might have multiple physical links to reach the peer. Each link is allocated a PeerAdj SID. When the device forwards traffic based on a PeerAdj SID, the traffic is forwarded out of the interface that is attached to the link identified by the PeerAdj SID.
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PeerNode-Adj SID —Identifies a peer node and identifies one or multiple adjacency links that can reach a peer node.
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PeerSet SID —Identifies a group of peer nodes in a BGP-EPE SRv6 peer set. A PeerSet SID corresponds to multiple PeerNode SIDs and PeerAdj SIDs. When the device forwards traffic based on a PeerSet SID, it distributes the traffic among multiple peers.
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