- Add the min-cache-ttl config knob.
- Add the override-cache-ttl config knob.

--- bin/named/config.c.orig	2021-05-12 10:45:51 UTC
+++ bin/named/config.c
@@ -182,6 +182,8 @@ options {\n\
 "	max-acache-size 16M;\n\
 	max-cache-size 90%;\n\
 	max-cache-ttl 604800; /* 1 week */\n\
+	min-cache-ttl 0; /* no minimal, zero is allowed */\n\
+	override-cache-ttl 0; /* do not override */\n\
 	max-clients-per-query 100;\n\
 	max-ncache-ttl 10800; /* 3 hours */\n\
 	max-recursion-depth 7;\n\
--- bin/named/server.c.orig	2021-05-12 10:45:51 UTC
+++ bin/named/server.c
@@ -3721,6 +3721,16 @@ configure_view(dns_view_t *view, dns_viewlist_t *viewl
 	}
 
 	obj = NULL;
+	result = ns_config_get(maps, "override-cache-ttl", &obj);
+	INSIST(result == ISC_R_SUCCESS);
+	view->overridecachettl = cfg_obj_asuint32(obj);
+
+	obj = NULL;
+	result = ns_config_get(maps, "min-cache-ttl", &obj);
+	INSIST(result == ISC_R_SUCCESS);
+	view->mincachettl = cfg_obj_asuint32(obj);
+
+	obj = NULL;
 	result = ns_config_get(maps, "max-cache-ttl", &obj);
 	INSIST(result == ISC_R_SUCCESS);
 	view->maxcachettl = cfg_obj_asuint32(obj);
--- lib/dns/include/dns/view.h.orig	2021-05-12 10:45:51 UTC
+++ lib/dns/include/dns/view.h
@@ -152,6 +152,8 @@ struct dns_view {
 	bool			requestnsid;
 	bool			sendcookie;
 	dns_ttl_t			maxcachettl;
+	dns_ttl_t			mincachettl;
+	dns_ttl_t			overridecachettl;
 	dns_ttl_t			maxncachettl;
 	uint32_t			nta_lifetime;
 	uint32_t			nta_recheck;
--- lib/dns/resolver.c.orig	2021-05-12 10:45:51 UTC
+++ lib/dns/resolver.c
@@ -5579,6 +5579,18 @@ cache_name(fetchctx_t *fctx, dns_message_t *rmessage,
 		}
 
 		/*
+		 * Enforce the configure cache TTL override.
+		 */
+                if (res->view->overridecachettl)
+                        rdataset->ttl = res->view->overridecachettl;
+
+		/*
+		 * Enforce the configure minimum cache TTL.
+		 */
+                if (rdataset->ttl < res->view->mincachettl)
+                        rdataset->ttl = res->view->mincachettl;
+
+		/*
 		 * Enforce the configure maximum cache TTL.
 		 */
 		if (rdataset->ttl > res->view->maxcachettl) {
--- lib/isccfg/namedconf.c.orig	2021-05-12 10:45:51 UTC
+++ lib/isccfg/namedconf.c
@@ -1773,6 +1773,8 @@ view_clauses[] = {
 #endif
 	{ "max-acache-size", &cfg_type_sizenodefault, 0 },
 	{ "max-cache-size", &cfg_type_sizeorpercent, 0 },
+	{ "override-cache-ttl", &cfg_type_uint32, 0 },
+	{ "min-cache-ttl", &cfg_type_uint32, 0 },
 	{ "max-cache-ttl", &cfg_type_uint32, 0 },
 	{ "max-clients-per-query", &cfg_type_uint32, 0 },
 	{ "max-ncache-ttl", &cfg_type_uint32, 0 },