Explains how Format 1 locators are replaced through preparation, dual-format underlay operation, overlay migration, SID replacement, and final removal from P and PE nodes.
Summary
The uSID f3216 migration involves Network nodes, IS-IS protocol, P nodes, PE nodes, BGP, EVPN, and SRv6. The process begins with network nodes being upgraded to support uSID f3216 and allow coexistence. Subsequently, IS-IS on P and PE nodes is configured to incrementally shift the underlay to f3216 while temporarily coexisting with format1. Finally, BGP and EVPN configurations on PE nodes are updated to migrate overlay services, with SRv6 managing the allocation and deallocation of SIDs. This systematic approach ensures a seamless transition to a fully uSID f3216-based network architecture.
Workflow
These stages describe how the uSID f3216 migration process works.
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Prepare for migration: Upgrade the network nodes to an image that is uSID f3216 capable, and allows the coexistence of format1 and f3216
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Migrate the underlay to uSID: IS-IS as an underlay protocol was already configured on P and PE nodes using format1 locators. In this migration step, add f3216 locators in the IS-IS configuration, in addition to the format1 locators. Both format1 and f3216 endpoint SIDs are concurrently allocated, installed, and announced during this stage. f3216 is the preferred option over format1 for underlay paths.
After the f3216 locators have been configured on all P and PE nodes, the format1 locators are removed from the P nodes. The overlay services still use the format1 locators after completing this migration step, therefore, the format1 locator configuration must be maintained on the PE nodes.
At the end of this step, the migration status of the P nodes is:
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Locator reachability: f3216 only
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Underlay endpoints/headends: f3216 only
At the end of this step, the migration status of the PE Nodes is:
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Locator reachability: format1 and f3216
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Underlay endpoints/headends: f3216 only
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Overlay endpoints/headends: format1
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Migrate the overlay to uSID: Enable overlay f3216 locators under BGP and EVPN on all PE nodes. The BGP and EVPN configurations replace the format1 locator with the f3216 locator. During this stage, the f3216 uSIDs are allocated, installed, and announced, while the format1 SIDs are deallocated, uninstalled, and withdrawn.
For a transient period, BGP and EVPN might have some paths with a format1 SID and some with an f3216 SID.
The format1 locators are removed from the underlay after all the overlay traffic has converged to use f3216 SIDs. By unconfiguring the format1 locators from BGP and EVPN, they are deleted from SRv6.
At the end of this step, the migration status of the P/PE Nodes is:
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Locator reachability: f3216 only
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Underlay endpoints/headends: f3216 only
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Overlay endpoints/headends: f3216 only
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Final state: This is the state of deployment at the end of the migration. At the end state, you can update the network and add new features. In the Full-Replace migration end state, both underlay and overlay are migrated to uSID f3216.