From 50bc5bbd0e7a5e74a606661b07a086106546ccc4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Asbj=C3=B8rn=20Sloth=20T=C3=B8nnesen?= <ast@2e8.dk>
Date: Sat, 16 May 2026 20:18:13 +0000
Subject: add support for IPv4 via IPv6 nexthop
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This is common with BGP (RFC 8950), but the underlying
principle is will soon have it's own RFC.

Example: (guest VM)
  ip addr add 192.0.2.42/32 dev lo
  ip route add proto static 0.0.0.0/0 via inet6 2001:db8:1337::1

RFC 8950: Advertising IPv4 NLRI with an IPv6 Next Hop
https://www.rfc-editor.org/rfc/rfc8950

draft-ietf-intarea-v4-via-v6: IPv4 routes with an IPv6 next hop
https://datatracker.ietf.org/doc/draft-ietf-intarea-v4-via-v6/

Signed-off-by: Asbjørn Sloth Tønnesen <ast@2e8.dk>
---
 qemu        | 9 +++++++--
 test-in.xml | 9 +++++++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/qemu b/qemu
index 9a20e74..5a63c63 100755
--- a/qemu
+++ b/qemu
@@ -45,7 +45,11 @@ xpath(){
 	echo "$2" | xmllint --xpath "$1" - 2>/dev/null
 }
 
-get_address_family(){ [ -z "${1##*:*}" ] && echo ipv6 || echo ipv4; }
+is_ipv6(){ [ -z "${1##*:*}" ]; }
+
+ip_family_select(){ is_ipv6 "$1" && echo "$3" || echo "$2"; }
+
+get_address_family(){ ip_family_select "$1" 'ipv4' 'ipv6'; }
 
 get_config(){
 	local configfile="$1"
@@ -138,8 +142,9 @@ process_route(){
 
 	local prefix; prefix="$(get_attr 'prefix' "$nodexml")"
 	local nexthop; nexthop="$(get_attr 'nexthop' "$nodexml")"
+	local nh_fam; nh_fam="inet$(ip_family_select "$nexthop" '' '6')"
 
-	ip route add proto static "$prefix" via "$nexthop"
+	ip route add proto static "$prefix" via "$nh_fam" "$nexthop"
 	return 0
 }
 
diff --git a/test-in.xml b/test-in.xml
index 59af475..7f5d8dd 100644
--- a/test-in.xml
+++ b/test-in.xml
@@ -14,6 +14,11 @@
         <gateway address="192.0.2.9/29"/>
         <host address="192.0.2.10"/>
       </interface>
+      <interface mac="fa:23:45:67:89:0a" mtu="4470">
+	<gateway address="2001:db8:1337::1/64"/>
+	<host address="2001:db8:1337::2"/>
+	<route prefix="192.0.2.42/32" nexthop="2001:db8:1337::2"/>
+      </interface>
     </routed-subnet>
   </metadata>
   <devices>
@@ -25,5 +30,9 @@
       <mac address="fa:12:34:ab:cd:ef"/>
       <target dev="bar0"/>
     </interface>
+    <interface type="ethernet">
+      <mac address="fa:23:45:67:89:0a"/>
+      <target dev="v6only"/>
+    </interface>
   </devices>
 </domain>
-- 
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