diff --git a/modules/retiolum/default.nix b/modules/retiolum/default.nix
index 4937150..c86a802 100644
--- a/modules/retiolum/default.nix
+++ b/modules/retiolum/default.nix
@@ -6,6 +6,7 @@ let
   netname = "retiolum";
   cfg = config.networking.retiolum;
   hosts = ../../hosts;
+  genipv6 = import ./genipv6.nix { inherit lib; };
 in {
   options = {
     networking.retiolum.ipv4 = mkOption {
@@ -17,6 +18,9 @@ in {
     };
     networking.retiolum.ipv6 = mkOption {
       type = types.str;
+      default = (genipv6 "retiolum" "external"  {
+        hostName = config.networking.hostName;
+      }).address;
       description = ''
         own ipv6 address
       '';
diff --git a/modules/retiolum/genipv6.nix b/modules/retiolum/genipv6.nix
new file mode 100644
index 0000000..b359232
--- /dev/null
+++ b/modules/retiolum/genipv6.nix
@@ -0,0 +1,198 @@
+# stolen from krebs/stockholm
+{ lib ? (import <nixpkgs> {}).lib }:
+with lib;
+let {
+  body = netname: subnetname: suffixSpec: rec {
+    address = let
+      suffix' = prependZeros suffixLength suffix;
+    in
+      normalize-ip6-addr
+        (checkAddress addressLength (joinAddress subnetPrefix suffix'));
+    addressCIDR = "${address}/${toString addressLength}";
+    addressLength = 128;
+
+    inherit netname;
+    netCIDR = "${netAddress}/${toString netPrefixLength}";
+    netAddress =
+      normalize-ip6-addr (appendZeros addressLength netPrefix);
+    netHash = toString {
+      retiolum = 0;
+      wiregrill = 1;
+    }.${netname};
+    netPrefix = "42:${netHash}";
+    netPrefixLength = {
+      retiolum = 32;
+      wiregrill = 32;
+    }.${netname};
+
+    inherit subnetname;
+    subnetCIDR = "${subnetAddress}/${toString subnetPrefixLength}";
+    subnetAddress =
+      normalize-ip6-addr (appendZeros addressLength subnetPrefix);
+    subnetHash = hashToLength 4 subnetname;
+    subnetPrefix = joinAddress netPrefix subnetHash;
+    subnetPrefixLength = netPrefixLength + 16;
+
+    suffix = getAttr (builtins.typeOf suffixSpec) {
+      set =
+        concatStringsSep
+          ":"
+          (stringToGroupsOf
+            4
+            (hashToLength (suffixLength / 4) suffixSpec.hostName));
+      string = suffixSpec;
+    };
+    suffixLength = addressLength - subnetPrefixLength;
+  };
+
+  appendZeros = n: s: let
+    n' = n / 16;
+    zeroCount = n' - length parsedaddr;
+    parsedaddr = parseAddress s;
+  in
+    formatAddress (parsedaddr ++ map (const "0") (range 1 zeroCount));
+
+  prependZeros = n: s: let
+    n' = n / 16;
+    zeroCount = n' - length parsedaddr;
+    parsedaddr = parseAddress s;
+  in
+    formatAddress (map (const "0") (range 1 zeroCount) ++ parsedaddr);
+
+  hasEmptyPrefix = xs: take 2 xs == ["" ""];
+  hasEmptySuffix = xs: takeLast 2 xs == ["" ""];
+  hasEmptyInfix = xs: any (x: x == "") (trimEmpty 2 xs);
+
+  hasEmptyGroup = xs:
+    any (p: p xs) [hasEmptyPrefix hasEmptyInfix hasEmptySuffix];
+
+  hashToLength = n: s: substring 0 n (builtins.hashString "sha256" s);
+
+  ltrimEmpty = n: xs: if hasEmptyPrefix xs then drop n xs else xs;
+  rtrimEmpty = n: xs: if hasEmptySuffix xs then dropLast n xs else xs;
+  trimEmpty = n: xs: rtrimEmpty n (ltrimEmpty n xs);
+
+  parseAddress = splitString ":";
+  formatAddress = concatStringsSep ":";
+
+  check = s: c: if !c then throw "${s}" else true;
+
+  checkAddress = maxaddrlen: addr: let
+    parsedaddr = parseAddress addr;
+    normalizedaddr = trimEmpty 1 parsedaddr;
+  in
+    assert (check "address malformed; lone leading colon: ${addr}" (
+      head parsedaddr == "" -> tail (take 2 parsedaddr) == ""
+    ));
+    assert (check "address malformed; lone trailing colon ${addr}" (
+      last parsedaddr == "" -> head (takeLast 2 parsedaddr) == ""
+    ));
+    assert (check "address malformed; too many successive colons: ${addr}" (
+      length (filter (x: x == "") normalizedaddr) > 1 -> addr == [""]
+    ));
+    assert (check "address malformed: ${addr}" (
+      all (test "[0-9a-f]{0,4}") parsedaddr
+    ));
+    assert (check "address is too long: ${addr}" (
+      length normalizedaddr * 16 <= maxaddrlen
+    ));
+    addr;
+
+  joinAddress = prefix: suffix: let
+    parsedPrefix = parseAddress prefix;
+    parsedSuffix = parseAddress suffix;
+    normalizePrefix = rtrimEmpty 2 parsedPrefix;
+    normalizeSuffix = ltrimEmpty 2 parsedSuffix;
+    delimiter =
+      optional (length (normalizePrefix ++ normalizeSuffix) < 8 &&
+                (hasEmptySuffix parsedPrefix || hasEmptyPrefix parsedSuffix))
+               "";
+  in
+    formatAddress (normalizePrefix ++ delimiter ++ normalizeSuffix);
+
+  # https://tools.ietf.org/html/rfc5952
+  normalize-ip6-addr =
+    let
+      max-run-0 =
+        let
+          both = v: { off = v; pos = v; };
+          gt = a: b: a.pos - a.off > b.pos - b.off;
+
+          chkmax = ctx: {
+            cur = both (ctx.cur.pos + 1);
+            max = if gt ctx.cur ctx.max then ctx.cur else ctx.max;
+          };
+
+          incpos = ctx: recursiveUpdate ctx {
+            cur.pos = ctx.cur.pos + 1;
+          };
+
+          f = ctx: blk: (if blk == "0" then incpos else chkmax) ctx;
+          z = { cur = both 0; max = both 0; };
+        in
+          blks: (chkmax (foldl' f z blks)).max;
+
+      group-zeros = a:
+        let
+          blks = splitString ":" a;
+          max = max-run-0 blks;
+          lhs = take max.off blks;
+          rhs = drop max.pos blks;
+        in
+          if max.pos == 0
+            then a
+            else let
+              sep =
+                if 8 - (length lhs + length rhs) == 1
+                  then ":0:"
+                  else "::";
+            in
+              "${concatStringsSep ":" lhs}${sep}${concatStringsSep ":" rhs}";
+
+      drop-leading-zeros =
+        let
+          f = block:
+            let
+              res = builtins.match "0*(.+)" block;
+            in
+              if res == null
+                then block # empty block
+                else elemAt res 0;
+        in
+          a: concatStringsSep ":" (map f (splitString ":" a));
+    in
+      a:
+        toLower
+          (if test ".*::.*" a
+            then a
+            else group-zeros (drop-leading-zeros a));
+
+  # Split string into list of chunks where each chunk is at most n chars long.
+  # The leftmost chunk might shorter.
+  # Example: stringToGroupsOf "123456" -> ["12" "3456"]
+  stringToGroupsOf = n: s: let
+    acc =
+      foldl'
+        (acc: c: if stringLength acc.chunk < n then {
+          chunk = acc.chunk + c;
+          chunks = acc.chunks;
+        } else {
+          chunk = c;
+          chunks = acc.chunks ++ [acc.chunk];
+        })
+        {
+          chunk = "";
+          chunks = [];
+        }
+        (stringToCharacters s);
+  in
+    filter (x: x != []) ([acc.chunk] ++ acc.chunks);
+
+
+  takeLast = n: xs: reverseList (take n (reverseList xs));
+
+  test = re: x: isString x && testString re x;
+
+  testString = re: x: builtins.match re x != null;
+
+}