diff --git a/code/bngblaster/src/bbl.c b/code/bngblaster/src/bbl.c
index b2f6e4c5..0b3b76b9 100644
--- a/code/bngblaster/src/bbl.c
+++ b/code/bngblaster/src/bbl.c
@@ -221,6 +221,7 @@ bbl_smear_job(timer_s *timer)
     UNUSED(timer);
     /* LCP Keepalive Interval */
     if(g_ctx->config.lcp_keepalive_interval) {
+        /* Adding 1 nanoseconds to enforce a dedicated timer bucket. */
         timer_smear_bucket(&g_ctx->timer_root, g_ctx->config.lcp_keepalive_interval, 1);
     }
 }
diff --git a/code/bngblaster/src/bbl_access.c b/code/bngblaster/src/bbl_access.c
index 7adccf7c..fc734250 100644
--- a/code/bngblaster/src/bbl_access.c
+++ b/code/bngblaster/src/bbl_access.c
@@ -410,12 +410,12 @@ bbl_access_igmp_initial_join(timer_s *timer)
             session->zapping_count = rand() % g_ctx->config.igmp_zap_count;
         }
 
-        /* Adding 1 nanosecond to enforce a dedicated timer bucket for zapping. */
-        timer_add_periodic(&g_ctx->timer_root, &session->timer_zapping, "IGMP Zapping", g_ctx->config.igmp_zap_interval, 1, session, &bbl_access_igmp_zapping);
+        /* Adding 2 nanoseconds to enforce a dedicated timer bucket for zapping. */
+        timer_add_periodic(&g_ctx->timer_root, &session->timer_zapping, "IGMP Zapping", g_ctx->config.igmp_zap_interval, 2, session, &bbl_access_igmp_zapping);
         LOG(IGMP, "IGMP (ID: %u) ZAPPING start zapping with interval %u\n",
             session->session_id, g_ctx->config.igmp_zap_interval);
 
-        timer_smear_bucket(&g_ctx->timer_root, g_ctx->config.igmp_zap_interval, 1);
+        timer_smear_bucket(&g_ctx->timer_root, g_ctx->config.igmp_zap_interval, 2);
     }
 }
 
diff --git a/code/bngblaster/src/bbl_config.c b/code/bngblaster/src/bbl_config.c
index 077b5dc4..29ed4bf4 100644
--- a/code/bngblaster/src/bbl_config.c
+++ b/code/bngblaster/src/bbl_config.c
@@ -1315,7 +1315,8 @@ json_parse_isis_config(json_t *isis, isis_config_s *isis_config)
     json_t *sub, *con, *c, *value = NULL;
     const char *s = NULL;
     int i, size;
-    
+    double number;
+
     isis_external_connection_s *connection = NULL;
 
     const char *schema[] = {
@@ -1447,7 +1448,12 @@ json_parse_isis_config(json_t *isis, isis_config_s *isis_config)
 
     value = json_object_get(isis, "hello-interval");
     if(json_is_number(value)) {
-        isis_config->hello_interval = json_number_value(value);
+        number = json_number_value(value);
+        if(number < 1 || number > UINT16_MAX) {
+            fprintf(stderr, "JSON config error: Invalid value for isis->hello-interval (1 - 65535)\n");
+            return false;
+        }
+        isis_config->hello_interval = number;
     } else {
         isis_config->hello_interval = ISIS_DEFAULT_HELLO_INTERVAL;
     }
@@ -1459,49 +1465,84 @@ json_parse_isis_config(json_t *isis, isis_config_s *isis_config)
 
     value = json_object_get(isis, "hold-time");
     if(json_is_number(value)) {
-        isis_config->hold_time = json_number_value(value);
+        number = json_number_value(value);
+        if(number < 1 || number > UINT16_MAX) {
+            fprintf(stderr, "JSON config error: Invalid value for isis->hold-time (1 - 65535)\n");
+            return false;
+        }
+        isis_config->hold_time = number;
     } else {
         isis_config->hold_time = ISIS_DEFAULT_HOLD_TIME;
     }
 
     value = json_object_get(isis, "lsp-lifetime");
     if(json_is_number(value)) {
-        isis_config->lsp_lifetime = json_number_value(value);
+        number = json_number_value(value);
+        if(number < ISIS_DEFAULT_LSP_LIFETIME_MIN || number > ISIS_DEFAULT_LSP_LIFETIME) {
+            fprintf(stderr, "JSON config error: Invalid value for isis->lsp-lifetime (330 - 65535)\n");
+            return false;
+        }
+        isis_config->lsp_lifetime = number;
     } else {
         isis_config->lsp_lifetime = ISIS_DEFAULT_LSP_LIFETIME;
     }
 
     value = json_object_get(isis, "lsp-refresh-interval");
     if(json_is_number(value)) {
-        isis_config->lsp_refresh_interval = json_number_value(value);
+        number = json_number_value(value);
+        if(number < 1 || number > UINT16_MAX) {
+            fprintf(stderr, "JSON config error: Invalid value for isis->lsp-refresh-interval (1 - 65535)\n");
+            return false;
+        }
+        isis_config->lsp_refresh_interval = number;
     } else {
         isis_config->lsp_refresh_interval = ISIS_DEFAULT_LSP_REFRESH_IVL;
     }
 
     value = json_object_get(isis, "lsp-retry-interval");
     if(json_is_number(value)) {
-        isis_config->lsp_retry_interval = json_number_value(value);
+        number = json_number_value(value);
+        if(number < 1 || number > UINT16_MAX) {
+            fprintf(stderr, "JSON config error: Invalid value for isis->lsp-retry-interval (1 - 65535)\n");
+            return false;
+        }
+        isis_config->lsp_retry_interval = number;
     } else {
         isis_config->lsp_retry_interval = ISIS_DEFAULT_LSP_RETRY_IVL;
     }
 
     value = json_object_get(isis, "lsp-tx-interval");
     if(json_is_number(value)) {
-        isis_config->lsp_tx_interval = json_number_value(value);
+        number = json_number_value(value);
+        if(number < 1 || number > UINT16_MAX) {
+            fprintf(stderr, "JSON config error: Invalid value for isis->lsp-tx-interval (1 - 65535)\n");
+            return false;
+        }
+        isis_config->lsp_tx_interval = number;
     } else {
         isis_config->lsp_tx_interval = ISIS_DEFAULT_LSP_TX_IVL_MS;
     }
 
     value = json_object_get(isis, "lsp-tx-window-size");
     if(json_is_number(value)) {
-        isis_config->lsp_tx_window_size = json_number_value(value);
+        number = json_number_value(value);
+        if(number < 1 || number > UINT16_MAX) {
+            fprintf(stderr, "JSON config error: Invalid value for isis->lsp-tx-window-size (1 - 65535)\n");
+            return false;
+        }
+        isis_config->lsp_tx_window_size = number;
     } else {
         isis_config->lsp_tx_window_size = ISIS_DEFAULT_LSP_WINDOWS_SIZE;
     }
 
     value = json_object_get(isis, "csnp-interval");
     if(json_is_number(value)) {
-        isis_config->csnp_interval = json_number_value(value);
+        number = json_number_value(value);
+        if(number < 1 || number > UINT16_MAX) {
+            fprintf(stderr, "JSON config error: Invalid value for isis->csnp-interval (1 - 65535)\n");
+            return false;
+        }
+        isis_config->csnp_interval = number;
     } else {
         isis_config->csnp_interval = ISIS_DEFAULT_CSNP_INTERVAL;
     }
diff --git a/code/bngblaster/src/isis/isis.c b/code/bngblaster/src/isis/isis.c
index 4ee52690..9fcd4f3a 100644
--- a/code/bngblaster/src/isis/isis.c
+++ b/code/bngblaster/src/isis/isis.c
@@ -76,7 +76,7 @@ isis_init() {
         }
 
         if(config->external_mrt_file) {
-            if(!isis_mrt_load(instance, config->external_mrt_file)) {
+            if(!isis_mrt_load(instance, config->external_mrt_file, true)) {
                 LOG(ISIS, "Failed to load MRT file %s\n", config->external_mrt_file);
                 return false;
             }
diff --git a/code/bngblaster/src/isis/isis_csnp.c b/code/bngblaster/src/isis/isis_csnp.c
index 1e580c51..714013cc 100644
--- a/code/bngblaster/src/isis/isis_csnp.c
+++ b/code/bngblaster/src/isis/isis_csnp.c
@@ -78,37 +78,52 @@ isis_csnp_job(timer_s *timer)
     while(next) {
         lsp = *hb_itor_datum(itor);
 
-        /* Calculate remaining lifetime and ignore if already expired. */
-        timespec_sub(&ago, &now, &lsp->timestamp);
-        if(ago.tv_sec < lsp->lifetime) {
-            remaining_lifetime = lsp->lifetime - ago.tv_sec;
-
-            if(tlv->len > UINT8_MAX-ISIS_LSP_ENTRY_LEN) {
-                /* Open next LSP entry TLV */
-                if(pdu.pdu_len+sizeof(isis_tlv_s)+ISIS_LSP_ENTRY_LEN > ISIS_MAX_PDU_LEN) {
-                    adjacency->csnp_start = lsp->id;
-                    break;
-                }
-                tlv = (isis_tlv_s *)PDU_CURSOR(&pdu);
-                tlv->type = ISIS_TLV_LSP_ENTRIES;
-                tlv->len = 0;
-                PDU_BUMP_WRITE_BUFFER(&pdu, sizeof(isis_tlv_s));
-            } else {
-                if(pdu.pdu_len+ISIS_LSP_ENTRY_LEN > ISIS_MAX_PDU_LEN) {
-                    /* All entries do not fit into single CSNP. */
-                    adjacency->csnp_start = lsp->id;
-                    break;
-                }
-            }
-            tlv->len+=sizeof(isis_lsp_entry_s);
-            entry = (isis_lsp_entry_s *)PDU_CURSOR(&pdu);
-            entry->lifetime = htobe16(remaining_lifetime);
-            entry->lsp_id = htobe64(lsp->id);
-            entry->seq = htobe32(lsp->seq);
-            entry->checksum = *(uint16_t*)PDU_OFFSET(&lsp->pdu, ISIS_OFFSET_LSP_CHECKSUM);
-            PDU_BUMP_WRITE_BUFFER(&pdu, sizeof(isis_lsp_entry_s));
-            entries++;
+        if(lsp->deleted) {
+            /* Ignore deleted LSP. */
+            next = hb_itor_next(itor);
+            continue;
         }
+
+        /* Calculate remaining lifetime. */
+        timespec_sub(&ago, &now, &lsp->timestamp);
+        if(lsp->expired || ago.tv_sec >= lsp->lifetime) {
+            /* Expired! */
+            remaining_lifetime = 0;
+        } else {
+            remaining_lifetime = lsp->lifetime - ago.tv_sec;
+        }
+
+        if(tlv->len > UINT8_MAX-ISIS_LSP_ENTRY_LEN) {
+            /* Open next LSP entry TLV. */
+            if(pdu.pdu_len+sizeof(isis_tlv_s)+ISIS_LSP_ENTRY_LEN > ISIS_MAX_PDU_LEN) {
+                adjacency->csnp_start = lsp->id;
+                break;
+            }
+            tlv = (isis_tlv_s *)PDU_CURSOR(&pdu);
+            tlv->type = ISIS_TLV_LSP_ENTRIES;
+            tlv->len = 0;
+            PDU_BUMP_WRITE_BUFFER(&pdu, sizeof(isis_tlv_s));
+        } else {
+            if(pdu.pdu_len+ISIS_LSP_ENTRY_LEN > ISIS_MAX_PDU_LEN) {
+                /* All entries do not fit into single CSNP. */
+                adjacency->csnp_start = lsp->id;
+                break;
+            }
+        }
+        tlv->len+=sizeof(isis_lsp_entry_s);
+        entry = (isis_lsp_entry_s *)PDU_CURSOR(&pdu);
+        entry->lsp_id = htobe64(lsp->id);
+        entry->seq = htobe32(lsp->seq);
+        if(remaining_lifetime) {
+            entry->lifetime = htobe16(remaining_lifetime);
+            entry->checksum = *(uint16_t*)PDU_OFFSET(&lsp->pdu, ISIS_OFFSET_LSP_CHECKSUM);
+        } else {
+            entry->lifetime = 0;
+            entry->checksum = 0;
+        }
+        PDU_BUMP_WRITE_BUFFER(&pdu, sizeof(isis_lsp_entry_s));
+        entries++;
+
         next = hb_itor_next(itor);
     }
     hb_itor_free(itor);
@@ -127,7 +142,7 @@ isis_csnp_job(timer_s *timer)
     }    
 
     if(!entries) {
-        /* Do not send empty PSNP. */
+        /* Do not send empty CSNP. */
         return;
     }
 
diff --git a/code/bngblaster/src/isis/isis_ctrl.c b/code/bngblaster/src/isis/isis_ctrl.c
index d29ee8ca..72900b0c 100644
--- a/code/bngblaster/src/isis/isis_ctrl.c
+++ b/code/bngblaster/src/isis/isis_ctrl.c
@@ -135,11 +135,18 @@ isis_ctrl_database_entries(hb_tree *lsdb)
     database = json_array();
     while(next) {
         lsp = *hb_itor_datum(itor);
+
+        if(lsp->deleted) {
+            /* Ignore deleted LSP. */
+            next = hb_itor_next(itor);
+            continue;
+        }
+
         timespec_sub(&ago, &now, &lsp->timestamp);
-        if(ago.tv_sec < lsp->lifetime) {
-            remaining_lifetime = lsp->lifetime - ago.tv_sec;
-        } else {
+        if(lsp->expired || ago.tv_sec >= lsp->lifetime) {
             remaining_lifetime = 0;
+        } else {
+            remaining_lifetime = lsp->lifetime - ago.tv_sec;
         }
 
         if(lsp->source.adjacency) {
@@ -253,7 +260,7 @@ isis_ctrl_load_mrt(int fd, uint32_t session_id __attribute__((unused)), json_t *
         return bbl_ctrl_status(fd, "error", 404, "ISIS instance not found");
     }
 
-    if(!isis_mrt_load(instance, file_path)) {
+    if(!isis_mrt_load(instance, file_path, false)) {
         return bbl_ctrl_status(fd, "error", 500, "failed to load ISIS MRT file");
     }
     return bbl_ctrl_status(fd, "ok", 200, NULL);
diff --git a/code/bngblaster/src/isis/isis_def.h b/code/bngblaster/src/isis/isis_def.h
index d81c6ca6..e7235862 100644
--- a/code/bngblaster/src/isis/isis_def.h
+++ b/code/bngblaster/src/isis/isis_def.h
@@ -63,6 +63,7 @@
 #define ISIS_DEFAULT_HELLO_INTERVAL     10
 #define ISIS_DEFAULT_CSNP_INTERVAL      30
 #define ISIS_DEFAULT_HOLD_TIME          30
+#define ISIS_DEFAULT_LSP_LIFETIME_MIN   330
 #define ISIS_DEFAULT_LSP_LIFETIME       65535
 #define ISIS_DEFAULT_LSP_RETRY_IVL      5
 #define ISIS_DEFAULT_LSP_REFRESH_IVL    300
@@ -70,7 +71,6 @@
 #define ISIS_DEFAULT_LSP_WINDOWS_SIZE   1
 
 #define ISIS_DEFAULT_TEARDOWN_TIME      5
-#define ISIS_DEFAULT_PURGE_LIFETIME     0
 
 #define ISIS_LSP_GC_INTERVAL            30
 
@@ -364,6 +364,7 @@ typedef struct isis_lsp_ {
 
     uint32_t refcount;
     bool expired;
+    bool deleted;
 
     uint32_t seq;           /* Sequence number */
     uint16_t lifetime;      /* Remaining lifetime */
diff --git a/code/bngblaster/src/isis/isis_lsp.c b/code/bngblaster/src/isis/isis_lsp.c
index 82369d33..779f2b85 100644
--- a/code/bngblaster/src/isis/isis_lsp.c
+++ b/code/bngblaster/src/isis/isis_lsp.c
@@ -207,6 +207,45 @@ isis_lsp_retry_job(timer_s *timer)
     }
 }
 
+void
+isis_lsp_purge_job(timer_s *timer)
+{
+    isis_lsp_s *lsp = timer->data;
+    lsp->expired = true;
+    lsp->deleted = true;
+}
+
+void
+isis_lsp_lifetime_job(timer_s *timer)
+{
+    isis_lsp_s *lsp = timer->data;
+    lsp->expired = true;
+
+    LOG(ISIS, "ISIS %s-LSP %s (source %s seq %u) lifetime expired (%us)\n", 
+        isis_level_string(lsp->level), 
+        isis_lsp_id_to_str(&lsp->id),
+        isis_source_string(lsp->source.type),
+        lsp->seq, lsp->lifetime);
+}
+
+void
+isis_lsp_lifetime(isis_lsp_s *lsp)
+{
+    timer_del(lsp->timer_refresh);
+    if(lsp->lifetime > 0) {
+        timer_add(&g_ctx->timer_root, 
+                  &lsp->timer_lifetime, 
+                  "ISIS LIFETIME", lsp->lifetime, 0, lsp,
+                  &isis_lsp_lifetime_job);
+    } else {
+        timer_add(&g_ctx->timer_root, 
+                  &lsp->timer_lifetime, 
+                  "ISIS PURGE", 60, 0, lsp,
+                  &isis_lsp_purge_job);
+    }
+    timer_no_smear(lsp->timer_lifetime);
+}
+
 void
 isis_lsp_refresh(isis_lsp_s *lsp)
 {
@@ -214,11 +253,6 @@ isis_lsp_refresh(isis_lsp_s *lsp)
 
     lsp->seq++;
     lsp->expired = false;
-    timer_add(&g_ctx->timer_root, 
-              &lsp->timer_lifetime, 
-              "ISIS LIFETIME", lsp->lifetime, 0, lsp,
-              &isis_lsp_lifetime_job);
-    timer_no_smear(lsp->timer_lifetime);
 
     *(uint32_t*)PDU_OFFSET(&lsp->pdu, ISIS_OFFSET_LSP_SEQ) = htobe32(lsp->seq);
     clock_gettime(CLOCK_MONOTONIC, &lsp->timestamp);
@@ -236,19 +270,6 @@ isis_lsp_refresh_job(timer_s *timer)
     isis_lsp_refresh(lsp);
 }
 
-void
-isis_lsp_lifetime_job(timer_s *timer)
-{
-    isis_lsp_s *lsp = timer->data;
-
-    LOG(ISIS, "ISIS %s-LSP %s (seq %u) lifetime expired\n", 
-        isis_level_string(lsp->level), 
-        isis_lsp_id_to_str(&lsp->id), 
-        lsp->seq);
-
-    lsp->expired = true;
-}
-
 void
 isis_lsp_sx_job(timer_s *timer)
 {
@@ -336,7 +357,9 @@ isis_lsp_final(isis_lsp_s *lsp)
     isis_pdu_update_len(pdu);
     isis_pdu_update_auth(pdu, lsp->auth_key);
     isis_pdu_update_lifetime(pdu, lsp->lifetime);
-    isis_pdu_update_checksum(pdu);
+    if(lsp->lifetime > 0) {
+        isis_pdu_update_checksum(pdu);
+    }
 }
 
 static isis_lsp_s *
@@ -348,6 +371,7 @@ isis_lsp_fragment(isis_instance_s *instance, uint8_t level, uint8_t fragment, bo
     isis_pdu_s *pdu = NULL;
 
     uint64_t lsp_id = htobe64(fragment);
+    uint16_t refresh_interval = 0;
 
     hb_tree *lsdb;
     void **search = NULL;
@@ -384,12 +408,17 @@ isis_lsp_fragment(isis_instance_s *instance, uint8_t level, uint8_t fragment, bo
 
     clock_gettime(CLOCK_MONOTONIC, &lsp->timestamp);
     if(purge || instance->teardown) {
-        lsp->lifetime = ISIS_DEFAULT_PURGE_LIFETIME;
-        timer_del(lsp->timer_refresh);
+        lsp->lifetime = 0;
+        isis_lsp_lifetime(lsp);
     } else {
         lsp->lifetime = config->lsp_lifetime;
+        refresh_interval = lsp->lifetime - 300;
+        if(config->lsp_refresh_interval < refresh_interval) {
+            refresh_interval = config->lsp_refresh_interval;
+        }
+        timer_del(lsp->timer_lifetime);
         timer_add_periodic(&g_ctx->timer_root, &lsp->timer_refresh, 
-                           "ISIS LSP refresh", config->lsp_refresh_interval, 0, lsp, 
+                           "ISIS LSP REFRESH", refresh_interval, 3, lsp, 
                            &isis_lsp_refresh_job);
     }
 
@@ -609,6 +638,8 @@ isis_lsp_handler_rx(bbl_network_interface_s *interface, isis_pdu_s *pdu, uint8_t
             /* Per default we will not overwrite 
              * external LSP. */
             if(config->external_auto_refresh) {
+                /* With external-auto-refresh enabled, 
+                 * the sequence number will be increased. */
                 lsp->seq = seq;
                 isis_lsp_refresh(lsp);
             }
@@ -647,12 +678,7 @@ isis_lsp_handler_rx(bbl_network_interface_s *interface, isis_pdu_s *pdu, uint8_t
     PDU_CURSOR_RST(pdu);
     memcpy(&lsp->pdu, pdu, sizeof(isis_pdu_s));
 
-    timer_add(&g_ctx->timer_root, 
-              &lsp->timer_lifetime, 
-              "ISIS LIFETIME", lsp->lifetime, 0, lsp,
-              &isis_lsp_lifetime_job);
-    timer_no_smear(lsp->timer_lifetime);
-
+    isis_lsp_lifetime(lsp);
     isis_lsp_flood(lsp);
 
 ACK:
@@ -704,10 +730,12 @@ isis_lsp_purge_external(isis_instance_s *instance, uint8_t level)
         lsp = *hb_itor_datum(itor);
         if(lsp && lsp->source.type == ISIS_SOURCE_EXTERNAL) {
             lsp->seq++;
-            lsp->lifetime = ISIS_DEFAULT_PURGE_LIFETIME;
             lsp->timestamp.tv_sec = now.tv_sec;
             lsp->timestamp.tv_nsec = now.tv_nsec;
-            timer_del(lsp->timer_refresh);
+
+            lsp->lifetime = 0;
+            lsp->expired = true;
+            isis_lsp_lifetime(lsp);
 
             /* Build PDU */
             pdu = &lsp->pdu;
@@ -721,7 +749,7 @@ isis_lsp_purge_external(isis_instance_s *instance, uint8_t level)
                 lsp->auth_key = config->level2_key;
             }
         
-            /* PDU header */
+            /* PDU header. */
             isis_pdu_add_u16(pdu, 0);
             isis_pdu_add_u16(pdu, 0);
             isis_pdu_add_u64(pdu, lsp->id);
@@ -729,14 +757,17 @@ isis_lsp_purge_external(isis_instance_s *instance, uint8_t level)
             isis_pdu_add_u16(pdu, 0);
             isis_pdu_add_u8(pdu, 0x03); 
 
-            /* TLV section */
+            /* TLV section. */
             isis_pdu_add_tlv_auth(pdu, auth_type, lsp->auth_key);
 
-            /* Update checksum... */
+            /* Update length and authentication. */
             isis_pdu_update_len(pdu);
             isis_pdu_update_auth(pdu, lsp->auth_key);
-            isis_pdu_update_lifetime(pdu, lsp->lifetime);
-            isis_pdu_update_checksum(pdu);
+
+            /* Set checksum and lifetime to zero. */
+            *(uint16_t*)PDU_OFFSET(pdu, ISIS_OFFSET_LSP_LIFETIME) = 0;
+            *(uint16_t*)PDU_OFFSET(pdu, ISIS_OFFSET_LSP_CHECKSUM) = 0;
+
             isis_lsp_flood(lsp);
         }
         next = hb_itor_next(itor);
@@ -752,10 +783,12 @@ isis_lsp_purge_external(isis_instance_s *instance, uint8_t level)
 bool
 isis_lsp_update_external(isis_instance_s *instance, isis_pdu_s *pdu)
 {
+    uint8_t level;
+
     isis_lsp_s *lsp = NULL;
-    uint64_t    lsp_id;
-    uint32_t    seq;
-    uint8_t     level;
+    uint64_t lsp_id;
+    uint32_t seq;
+    uint16_t refresh_interval = 0;
 
     hb_tree *lsdb;
     void **search = NULL;
@@ -772,7 +805,7 @@ isis_lsp_update_external(isis_instance_s *instance, isis_pdu_s *pdu)
     lsp_id = be64toh(*(uint64_t*)PDU_OFFSET(pdu, ISIS_OFFSET_LSP_ID));
     seq = be32toh(*(uint32_t*)PDU_OFFSET(pdu, ISIS_OFFSET_LSP_SEQ));
 
-    LOG(DEBUG, "ISIS UPDATE %s-LSP %s (seq %u) from command\n", 
+    LOG(ISIS, "ISIS UPDATE %s-LSP %s (seq %u) from command\n", 
         isis_level_string(level), 
         isis_lsp_id_to_str(&lsp_id), 
         seq);
@@ -807,11 +840,24 @@ isis_lsp_update_external(isis_instance_s *instance, isis_pdu_s *pdu)
     PDU_CURSOR_RST(pdu);
     memcpy(&lsp->pdu, pdu, sizeof(isis_pdu_s));
 
-    timer_add(&g_ctx->timer_root, 
-              &lsp->timer_lifetime, 
-              "ISIS LIFETIME", lsp->lifetime, 0, lsp,
-              &isis_lsp_lifetime_job);
-    timer_no_smear(lsp->timer_lifetime);
+    if(lsp->lifetime > 0 && instance->config->external_auto_refresh) {
+        if(level == ISIS_LEVEL_1) {
+            lsp->auth_key = instance->config->level1_key;
+        } else {
+            lsp->auth_key = instance->config->level2_key;
+        }
+        if(lsp->lifetime < ISIS_DEFAULT_LSP_LIFETIME_MIN) {
+            /* Increase ISIS lifetime. */
+            lsp->lifetime = ISIS_DEFAULT_LSP_LIFETIME_MIN;
+            isis_lsp_refresh(lsp); 
+        }
+        refresh_interval = lsp->lifetime - 300;
+        timer_add_periodic(&g_ctx->timer_root, &lsp->timer_refresh, 
+                            "ISIS LSP REFRESH", refresh_interval, 3, lsp, 
+                            &isis_lsp_refresh_job);
+    } else {
+        isis_lsp_lifetime(lsp);
+    }
 
     isis_lsp_flood(lsp);
     return true;
diff --git a/code/bngblaster/src/isis/isis_lsp.h b/code/bngblaster/src/isis/isis_lsp.h
index 2bcea116..cc156f9a 100644
--- a/code/bngblaster/src/isis/isis_lsp.h
+++ b/code/bngblaster/src/isis/isis_lsp.h
@@ -24,11 +24,14 @@ isis_lsp_gc_job(timer_s *timer);
 void
 isis_lsp_retry_job(timer_s *timer);
 
+void
+isis_lsp_refresh(isis_lsp_s *lsp);
+
 void
 isis_lsp_refresh_job(timer_s *timer);
 
 void
-isis_lsp_lifetime_job(timer_s *timer);
+isis_lsp_lifetime(isis_lsp_s *lsp);
 
 void
 isis_lsp_sx_job(timer_s *timer);
diff --git a/code/bngblaster/src/isis/isis_mrt.c b/code/bngblaster/src/isis/isis_mrt.c
index 0b6ce503..99071412 100644
--- a/code/bngblaster/src/isis/isis_mrt.c
+++ b/code/bngblaster/src/isis/isis_mrt.c
@@ -9,7 +9,7 @@
 #include "isis.h"
 
 bool
-isis_mrt_load(isis_instance_s *instance, char *file_path)
+isis_mrt_load(isis_instance_s *instance, char *file_path, bool startup)
 {
     FILE *mrt_file;
 
@@ -21,6 +21,7 @@ isis_mrt_load(isis_instance_s *instance, char *file_path)
     isis_lsp_s *lsp = NULL;
     uint64_t lsp_id;
     uint32_t seq;
+    uint16_t refresh_interval = 0;
 
     hb_tree *lsdb;
     void **search = NULL;
@@ -117,26 +118,31 @@ isis_mrt_load(isis_instance_s *instance, char *file_path)
         PDU_CURSOR_RST(&pdu);
         memcpy(&lsp->pdu, &pdu, sizeof(isis_pdu_s));
 
-        if(instance->config->external_auto_refresh) {
+        if(lsp->lifetime > 0 && instance->config->external_auto_refresh) {
             if(level == ISIS_LEVEL_1) {
                 lsp->auth_key = instance->config->level1_key;
             } else {
                 lsp->auth_key = instance->config->level2_key;
             }
-            if(lsp->lifetime < 330) {
-                lsp->lifetime = 300;
+            if(lsp->lifetime < ISIS_DEFAULT_LSP_LIFETIME_MIN) {
+                /* Increase ISIS lifetime. */
+                lsp->lifetime = ISIS_DEFAULT_LSP_LIFETIME_MIN;
+                isis_lsp_refresh(lsp); 
             }
+            refresh_interval = lsp->lifetime - 300;
             timer_add_periodic(&g_ctx->timer_root, &lsp->timer_refresh, 
-                               "ISIS LSP refresh", lsp->lifetime - 300, 0, lsp, 
+                               "ISIS LSP REFRESH", refresh_interval, 3, lsp, 
                                &isis_lsp_refresh_job);
+        } else {
+            isis_lsp_lifetime(lsp);
         }
-
-        timer_add(&g_ctx->timer_root, 
-                  &lsp->timer_lifetime, 
-                  "ISIS LIFETIME", lsp->lifetime, 0, lsp,
-                  &isis_lsp_lifetime_job);
-        timer_no_smear(lsp->timer_lifetime);
     }
+
+    if(startup && refresh_interval) {
+        /* Adding 3 nanoseconds to enforce a dedicated timer bucket. */
+        timer_smear_bucket(&g_ctx->timer_root, refresh_interval, 3);
+    }
+
     fclose(mrt_file);
     return true;
 }
\ No newline at end of file
diff --git a/code/bngblaster/src/isis/isis_mrt.h b/code/bngblaster/src/isis/isis_mrt.h
index f4a45999..c6e3f1fe 100644
--- a/code/bngblaster/src/isis/isis_mrt.h
+++ b/code/bngblaster/src/isis/isis_mrt.h
@@ -19,6 +19,6 @@ typedef struct isis_mrt_hdr_ {
 } __attribute__ ((__packed__)) isis_mrt_hdr_t;
 
 bool
-isis_mrt_load(isis_instance_s *instance, char *file_path);
+isis_mrt_load(isis_instance_s *instance, char *file_path, bool startup);
 
 #endif
\ No newline at end of file
diff --git a/code/bngblaster/src/isis/isis_p2p_hello.c b/code/bngblaster/src/isis/isis_p2p_hello.c
index c02f666c..2cc11d7a 100644
--- a/code/bngblaster/src/isis/isis_p2p_hello.c
+++ b/code/bngblaster/src/isis/isis_p2p_hello.c
@@ -207,13 +207,16 @@ isis_p2p_hello_handler_rx(bbl_network_interface_s *interface, isis_pdu_s *pdu)
         }
     }
 
-    if(adjacency->state != new_state && new_state == ISIS_P2P_ADJACENCY_STATE_UP) {
-        for(int i=0; i<ISIS_LEVELS; i++) {
-            if(interface->isis_adjacency[i]) {
-                isis_adjacency_up(interface->isis_adjacency[i]);
-                isis_lsp_self_update(adjacency->instance, i+1);
+    if(adjacency->state != new_state) {
+        interface->send_requests |= BBL_IF_SEND_ISIS_P2P_HELLO;
+        if(new_state == ISIS_P2P_ADJACENCY_STATE_UP) {
+            for(int i=0; i<ISIS_LEVELS; i++) {
+                if(interface->isis_adjacency[i]) {
+                    isis_adjacency_up(interface->isis_adjacency[i]);
+                    isis_lsp_self_update(adjacency->instance, i+1);
+                }
             }
         }
+        adjacency->state = new_state;
     }
-    adjacency->state = new_state;
 }
\ No newline at end of file
diff --git a/code/bngblaster/src/isis/isis_pdu.c b/code/bngblaster/src/isis/isis_pdu.c
index 2e5a7832..38cbf6f6 100644
--- a/code/bngblaster/src/isis/isis_pdu.c
+++ b/code/bngblaster/src/isis/isis_pdu.c
@@ -231,17 +231,19 @@ isis_pdu_update_auth(isis_pdu_s *pdu, char *key)
 bool
 isis_pdu_validate_checksum(isis_pdu_s *pdu)
 {
-    uint16_t checksum;
-    uint16_t checksum_orig;
+    uint16_t checksum = 0;
+    uint16_t checksum_orig = 0;
 
-    switch (pdu->pdu_type) {
+    switch(pdu->pdu_type) {
         case ISIS_PDU_L1_LSP:
         case ISIS_PDU_L2_LSP:
             checksum_orig = *(uint16_t*)PDU_OFFSET(pdu, ISIS_OFFSET_LSP_CHECKSUM);
-            checksum = isis_checksum_fletcher16(
-                pdu->pdu+ISIS_OFFSET_LSP_ID, 
-                pdu->pdu_len-ISIS_OFFSET_LSP_ID, 
-                ISIS_OFFSET_LSP_CHECKSUM-ISIS_OFFSET_LSP_ID);
+            if(checksum_orig > 0) {
+                checksum = isis_checksum_fletcher16(
+                    pdu->pdu+ISIS_OFFSET_LSP_ID, 
+                    pdu->pdu_len-ISIS_OFFSET_LSP_ID, 
+                    ISIS_OFFSET_LSP_CHECKSUM-ISIS_OFFSET_LSP_ID);
+            }
             break;
         default:
             return true;
diff --git a/code/bngblaster/src/isis/isis_psnp.c b/code/bngblaster/src/isis/isis_psnp.c
index c76b733b..3f50be52 100644
--- a/code/bngblaster/src/isis/isis_psnp.c
+++ b/code/bngblaster/src/isis/isis_psnp.c
@@ -70,39 +70,49 @@ isis_psnp_job (timer_s *timer)
         lsp = *search;
         hb_tree_remove(adjacency->psnp_tree, &lsp->id);
 
-        /* Calculate remaining lifetime and ignore if already expired. */
-        timespec_sub(&ago, &now, &lsp->timestamp);
-        if(ago.tv_sec < lsp->lifetime) {
-            remaining_lifetime = lsp->lifetime - ago.tv_sec;
-
-            if(tlv->len > UINT8_MAX-ISIS_LSP_ENTRY_LEN) {
-                /* Open next LSP entry TLV */
-                if(pdu.pdu_len+sizeof(isis_tlv_s)+ISIS_LSP_ENTRY_LEN > ISIS_MAX_PDU_LEN) {
-                    adjacency->csnp_start = lsp->id;
-                    break;
-                }
-                tlv = (isis_tlv_s *)PDU_CURSOR(&pdu);
-                tlv->type = ISIS_TLV_LSP_ENTRIES;
-                tlv->len = 0;
-                PDU_BUMP_WRITE_BUFFER(&pdu, sizeof(isis_tlv_s));
-            } else {
-                if(pdu.pdu_len+ISIS_LSP_ENTRY_LEN > ISIS_MAX_PDU_LEN) {
-                    /* All entries do not fit into single PSNP. */
-                    adjacency->timer_psnp_started = true;
-                    timer_add(&g_ctx->timer_root, &adjacency->timer_psnp_next, 
-                              "ISIS PSNP", 0, 10*MSEC, adjacency, &isis_psnp_job);
-                    break;
-                }
-            }
-            tlv->len+=sizeof(isis_lsp_entry_s);
-            entry = (isis_lsp_entry_s *)PDU_CURSOR(&pdu);
-            entry->lifetime = htobe16(remaining_lifetime);
-            entry->lsp_id = htobe64(lsp->id);
-            entry->seq = htobe32(lsp->seq);
-            entry->checksum = *(uint16_t*)PDU_OFFSET(&lsp->pdu, ISIS_OFFSET_LSP_CHECKSUM);
-            PDU_BUMP_WRITE_BUFFER(&pdu, sizeof(isis_lsp_entry_s));
-            entries++;
+        if(lsp->deleted) {
+            /* Ignore deleted LSP. */
+            search = hb_tree_search_gt(adjacency->psnp_tree, &lsp_id_zero);
+            continue;
         }
+
+        /* Calculate remaining lifetime. */
+        timespec_sub(&ago, &now, &lsp->timestamp);
+        if(lsp->expired || ago.tv_sec >= lsp->lifetime) {
+            /* Expired! */
+            remaining_lifetime = 0;
+        } else {
+            remaining_lifetime = lsp->lifetime - ago.tv_sec;
+        }
+
+        if(tlv->len > UINT8_MAX-ISIS_LSP_ENTRY_LEN) {
+            /* Open next LSP entry TLV. */
+            if(pdu.pdu_len+sizeof(isis_tlv_s)+ISIS_LSP_ENTRY_LEN > ISIS_MAX_PDU_LEN) {
+                adjacency->csnp_start = lsp->id;
+                break;
+            }
+            tlv = (isis_tlv_s *)PDU_CURSOR(&pdu);
+            tlv->type = ISIS_TLV_LSP_ENTRIES;
+            tlv->len = 0;
+            PDU_BUMP_WRITE_BUFFER(&pdu, sizeof(isis_tlv_s));
+        } else {
+            if(pdu.pdu_len+ISIS_LSP_ENTRY_LEN > ISIS_MAX_PDU_LEN) {
+                /* All entries do not fit into single PSNP. */
+                adjacency->timer_psnp_started = true;
+                timer_add(&g_ctx->timer_root, &adjacency->timer_psnp_next, 
+                          "ISIS PSNP", 0, 10*MSEC, adjacency, &isis_psnp_job);
+                break;
+            }
+        }
+        tlv->len+=sizeof(isis_lsp_entry_s);
+        entry = (isis_lsp_entry_s *)PDU_CURSOR(&pdu);
+        entry->lifetime = htobe16(remaining_lifetime);
+        entry->lsp_id = htobe64(lsp->id);
+        entry->seq = htobe32(lsp->seq);
+        entry->checksum = *(uint16_t*)PDU_OFFSET(&lsp->pdu, ISIS_OFFSET_LSP_CHECKSUM);
+        PDU_BUMP_WRITE_BUFFER(&pdu, sizeof(isis_lsp_entry_s));
+        entries++;
+
         search = hb_tree_search_gt(adjacency->psnp_tree, &lsp_id_zero);
     }
     isis_pdu_update_len(&pdu);