Using shell commands:

nft add table ip filter
nft add map filter deucalion { type ipv4_addr : classid\; }

Using nftables file:

deucalion.nft

table ip filter {
	map deucalion {
		type ipv4_addr : classid;
		elements = { 1.1.1.2 : 2:2222, 1.1.1.3 : 3:3333 }
	}
 
 
	chain input {
		type filter hook input priority 0; policy accept;
		meta priority set ip daddr map @deucalion;
	}
}

This patch is already merged upstream (as of 2018 Archlinux and Ubuntu have it, Debian not yet!):

• https://www.spinics.net/lists/netfilter/msg57694.html
• https://www.spinics.net/lists/netfilter/threads.html#57694

You need it if nft shows this error:

<cmdline>:1:45-51: Error: syntax error, unexpected classid, expecting string or dscp or ecn or mark
add map filter deucalion { type ipv4_addr : classid; }
                                            ^^^^^^^
<cmdline>:1:26-52: Error: map definition does not specify key data type
add map filter deucalion { type ipv4_addr : classid; }
                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^

nft-classid.patch

parser: allow classid as set key
 
From: Arturo Borrero Gonzalez <arturo@xxxxxxxxxxxxx>
 
Allow TC classid as set key.
 
Signed-off-by: Arturo Borrero Gonzalez <arturo@xxxxxxxxxxxxx>
---
 src/parser_bison.y |    1 +
 1 file changed, 1 insertion(+)
 
diff --git a/src/parser_bison.y b/src/parser_bison.y
index 7016f5b..2918875 100644
--- a/src/parser_bison.y
+++ b/src/parser_bison.y
@@ -1545,6 +1545,7 @@ type_identifier		:	STRING	{ $$ = $1; }
 			|	MARK	{ $$ = xstrdup("mark"); }
 			|	DSCP	{ $$ = xstrdup("dscp"); }
 			|	ECN	{ $$ = xstrdup("ecn"); }
+			|	CLASSID { $$ = xstrdup("classid"); }
 			;
 
 hook_spec		:	TYPE		STRING		HOOK		STRING		dev_spec	PRIORITY	prio_spec