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Document NixlConnector backend selection via kv_connector_extra_config (#33552)

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Signed-off-by: KrxGu <krishom70@gmail.com>
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Krish Gupta
2026-02-03 19:19:59 +05:30
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docs/features/nixl_connector_usage.md
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@@ -36,6 +36,35 @@ export UCX_NET_DEVICES=all # or specify network devices like "mlx5_0:1,mlx5_1:1
!!! tip
When using UCX as the transport backend, NCCL environment variables (like `NCCL_IB_HCA`, `NCCL_SOCKET_IFNAME`) are not applicable to NixlConnector, so configure UCX-specific environment variables instead of NCCL variables.
#### Selecting a NIXL transport backend (plugin)
NixlConnector can use different NIXL transport backends (plugins). By default, NixlConnector uses UCX as the transport backend.
To select a different backend, set `kv_connector_extra_config.backends` in `--kv-transfer-config`.
### Example: using LIBFABRIC backend
```bash
vllm serve <MODEL> \
--kv-transfer-config '{
"kv_connector":"NixlConnector",
"kv_role":"kv_both",
"kv_connector_extra_config":{"backends":["LIBFABRIC"]}
}'
```
You can also pass JSON keys individually using dotted arguments, and you can append list elements using `+`:
```bash
vllm serve <MODEL> \
--kv-transfer-config.kv_connector NixlConnector \
--kv-transfer-config.kv_role kv_both \
--kv-transfer-config.kv_connector_extra_config.backends+ LIBFABRIC
```
!!! note
Backend availability depends on how NIXL was built and what plugins are present in your environment. Refer to the [NIXL repository](https://github.com/ai-dynamo/nixl) for available backends and build instructions.
## Basic Usage (on the same host)
### Producer (Prefiller) Configuration