diff --git a/openbsc/src/osmo-bsc_nat/bsc_nat_rewrite_trie.c b/openbsc/src/osmo-bsc_nat/bsc_nat_rewrite_trie.c
new file mode 100644
index 0000000..57043ac
--- /dev/null
+++ b/openbsc/src/osmo-bsc_nat/bsc_nat_rewrite_trie.c
@@ -0,0 +1,240 @@
+/* Handling for loading a re-write file/database */
+/*
+ * (C) 2013 by On-Waves
+ * (C) 2013 by Holger Hans Peter Freyther <zecke@selfish.org>
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include <openbsc/nat_rewrite_trie.h>
+#include <openbsc/debug.h>
+
+#include <osmocom/core/talloc.h>
+#include <osmocom/core/utils.h>
+
+#include <assert.h>
+#include <stdio.h>
+#include <string.h>
+#include <ctype.h>
+
+#define CHECK_IS_DIGIT_OR_FAIL(prefix, pos)						\
+	if (!isdigit(prefix[pos]) && prefix[pos] != '+') {				\
+			LOGP(DNAT, LOGL_ERROR,						\
+				"Prefix(%s) contains non ascii text at(%d=%c)\n",	\
+				prefix, pos, prefix[pos]);				\
+			goto fail;							\
+	}
+#define TO_INT(c) \
+	((c) == '+' ? 10 : ((c - '0') % 10))
+
+static void insert_rewrite_node(struct nat_rewrite_rule *rule, struct nat_rewrite *root)
+{
+	struct nat_rewrite_rule *new = &root->rule;
+
+	const size_t len = strlen(rule->prefix);
+	int i;
+
+	if (len == 0) {
+		LOGP(DNAT, LOGL_ERROR, "An empty prefix does not make sense.\n");
+		goto fail;
+	}
+
+	for (i = 0; i < len - 1; ++i) {
+		int pos;
+
+		/* check if the input is valid */
+		CHECK_IS_DIGIT_OR_FAIL(rule->prefix, i);
+
+		/* check if the next node is already valid */
+		pos = TO_INT(rule->prefix[i]);
+		if (!new->rules[pos]) {
+			new->rules[pos] = talloc_zero(root, struct nat_rewrite_rule);
+			if (!new->rules[pos]) {
+				LOGP(DNAT, LOGL_ERROR,
+					"Failed to allocate memory.\n");
+				goto fail;
+			}
+
+			new->rules[pos]->empty = 1;
+		}
+
+		/* we continue here */
+		new = new->rules[pos];
+	}
+
+	/* new now points to the place where we want to add it */
+	int pos;
+
+	/* check if the input is valid */
+	CHECK_IS_DIGIT_OR_FAIL(rule->prefix, (len - 1));
+
+	/* check if the next node is already valid */
+	pos = TO_INT(rule->prefix[len - 1]);
+	if (!new->rules[pos])
+		new->rules[pos] = rule;
+	else if (new->rules[pos]->empty) {
+		/* copy over entries */
+		new->rules[pos]->empty = 0;
+		memcpy(new->rules[pos]->prefix, rule->prefix, sizeof(rule->prefix));
+		memcpy(new->rules[pos]->rewrite, rule->rewrite, sizeof(rule->rewrite));
+		talloc_free(rule);
+	} else {
+		LOGP(DNAT, LOGL_ERROR,
+			"Prefix(%s) is already installed\n", rule->prefix);
+		goto fail;
+	}
+
+	root->prefixes += 1;
+	return;
+
+fail:
+	talloc_free(rule);
+	return;
+}
+
+static void handle_line(struct nat_rewrite *rewrite, char *line)
+{
+	char *split;
+	struct nat_rewrite_rule *rule;
+	size_t size_prefix, size_end, len;
+
+
+	/* Find the ',' in the line */
+	len = strlen(line);
+	split = strstr(line, ",");
+	if (!split) {
+		LOGP(DNAT, LOGL_ERROR, "Line doesn't contain ','\n");
+		return;
+	}
+
+	/* Check if there is space for the rewrite rule */
+	size_prefix = split - line;
+	if (len - size_prefix <= 2) {
+		LOGP(DNAT, LOGL_ERROR, "No rewrite available.\n");
+		return;
+	}
+
+	/* Continue after the ',' to the end */
+	split = &line[size_prefix + 1];
+	size_end = strlen(split) - 1;
+
+	/* Check if both strings can fit into the static array */
+	if (size_prefix > sizeof(rule->prefix) - 1) {
+		LOGP(DNAT, LOGL_ERROR,
+			"Prefix is too long with %zu\n", size_prefix);
+		return;
+	}
+
+	if (size_end > sizeof(rule->rewrite) - 1) {
+		LOGP(DNAT, LOGL_ERROR,
+			"Rewrite is too long with %zu on %s\n",
+			size_end, &line[size_prefix + 1]);
+		return;
+	}
+
+	/* Now create the entry and insert it into the trie */
+	rule = talloc_zero(rewrite, struct nat_rewrite_rule);
+	if (!rule) {
+		LOGP(DNAT, LOGL_ERROR, "Can not allocate memory\n");
+		return;
+	}
+
+	memcpy(rule->prefix, line, size_prefix);
+	assert(size_prefix < sizeof(rule->prefix));
+	rule->prefix[size_prefix] = '\0';
+
+	memcpy(rule->rewrite, split, size_end);
+	assert(size_end < sizeof(rule->rewrite));
+	rule->rewrite[size_end] = '\0';
+
+	/* now insert and balance the tree */
+	insert_rewrite_node(rule, rewrite);
+}
+
+struct nat_rewrite *nat_rewrite_parse(void *ctx, const char *filename)
+{
+	FILE *file;
+	char *line = NULL;
+	size_t n = 2342;
+	struct nat_rewrite *res;
+
+	file = fopen(filename, "r");
+	if (!file)
+		return NULL;
+
+	res = talloc_zero(ctx, struct nat_rewrite);
+	if (!res) {
+		fclose(file);
+		return NULL;
+	}
+
+	/* mark the root as empty */
+	res->rule.empty = 1;
+
+	while (getline(&line, &n, file) != -1) {
+		handle_line(res, line);
+	}
+
+	free(line);
+	fclose(file);
+	return res;
+}
+
+/**
+ * Simple find that tries to do a longest match...
+ */
+struct nat_rewrite_rule *nat_rewrite_lookup(struct nat_rewrite *rewrite,
+					const char *prefix)
+{
+	struct nat_rewrite_rule *rule = &rewrite->rule;
+	struct nat_rewrite_rule *last = NULL;
+	const int len = OSMO_MIN(strlen(prefix), (sizeof(rule->prefix) - 1));
+	int i;
+
+	for (i = 0; rule && i < len; ++i) {
+		int pos;
+
+		CHECK_IS_DIGIT_OR_FAIL(prefix, i);
+		pos = TO_INT(prefix[i]);
+
+		rule = rule->rules[pos];
+		if (rule && !rule->empty)
+			last = rule;
+	}
+
+	return last;
+
+fail:
+	return NULL;
+}
+
+static void nat_rewrite_dump_rec(struct nat_rewrite_rule *rule)
+{
+	int i;
+	if (!rule->empty)
+		printf("%s,%s\n", rule->prefix, rule->rewrite);
+
+	for (i = 0; i < ARRAY_SIZE(rule->rules); ++i) {
+		if (!rule->rules[i])
+			continue;
+		nat_rewrite_dump_rec(rule->rules[i]);
+	}
+}
+
+void nat_rewrite_dump(struct nat_rewrite *rewrite)
+{
+	nat_rewrite_dump_rec(&rewrite->rule);
+}