+- ``<udf_id>``: Logical UDF id.
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+- ``<proto>``: Indicate the preceding hdr before the UDF header (`eth` or `udp`).
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+- ``<field>``: Indicate the field of the <proto> hdr (`type` (eth) or `dport` (udp).
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+- ``<key>``: UDF key in string format starting with '0x'.
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+- ``<mask>``: UDF mask in string format starting with '0x'.
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+- ``<offset>``: Starting UDF offset from the <proto> hdr.
+