BGP: Add support for BGP hostname capability

This is an implementation of draft-walton-bgp-hostname-capability-02.
It is implemented since quite some time for FRR and in datacenter, this
gives a nice output to avoid using IP addresses.

It is disabled by default. The hostname is retrieved from uname(2) and
can be overriden with "hostname" option. The domain name is never set
nor displayed.

Minor changes by committer.

proto/bgp/bgp.c

@@ -103,6 +103,7 @@
  * RFC 8654 - Extended Message Support for BGP
  * draft-ietf-idr-ext-opt-param-07
  * draft-uttaro-idr-bgp-persistence-04
+ * draft-walton-bgp-hostname-capability-02
  */
 
 #undef LOCAL_DEBUG
@@ -2415,6 +2416,9 @@ bgp_show_capabilities(struct bgp_proto *p UNUSED, struct bgp_caps *caps)
     bgp_show_afis(-1006, "        AF supported:", afl1, afn1);
     bgp_show_afis(-1006, "        AF preserved:", afl2, afn2);
   }
+
+  if (caps->hostname)
+    cli_msg(-1006, "      Hostname: %s", caps->hostname);
 }
 
 static void

proto/bgp/bgp.h

@@ -98,6 +98,7 @@ struct bgp_config {
   int enable_refresh;			/* Enable local support for route refresh [RFC 2918] */
   int enable_as4;			/* Enable local support for 4B AS numbers [RFC 6793] */
   int enable_extended_messages;		/* Enable local support for extended messages [draft] */
+  int enable_hostname;			/* Enable local support for hostname [draft] */
   u32 rr_cluster_id;			/* Route reflector cluster ID, if different from local ID */
   int rr_client;			/* Whether neighbor is RR client of me */
   int rs_client;			/* Whether neighbor is RS client of me */
@@ -228,6 +229,8 @@ struct bgp_caps {
   u8 any_ext_next_hop;			/* Bitwise OR of per-AF ext_next_hop */
   u8 any_add_path;			/* Bitwise OR of per-AF add_path */
 
+  const char *hostname;			/* Hostname, RFC draft */
+
   u16 af_count;				/* Number of af_data items */
   u16 length;				/* Length of capabilities in OPEN msg */
 

proto/bgp/config.Y

@@ -62,6 +62,7 @@ bgp_proto_start: proto_start BGP {
      BGP_CFG->error_delay_time_max = 300;
      BGP_CFG->enable_refresh = 1;
      BGP_CFG->enable_as4 = 1;
+     BGP_CFG->enable_hostname = 0;
      BGP_CFG->capabilities = 2;
      BGP_CFG->interpret_communities = 1;
      BGP_CFG->allow_as_sets = 1;
@@ -173,6 +174,7 @@ bgp_proto:
  | bgp_proto ENABLE ROUTE REFRESH bool ';' { BGP_CFG->enable_refresh = $5; }
  | bgp_proto ENABLE AS4 bool ';' { BGP_CFG->enable_as4 = $4; }
  | bgp_proto ENABLE EXTENDED MESSAGES bool ';' { BGP_CFG->enable_extended_messages = $5; }
+ | bgp_proto ADVERTISE HOSTNAME bool ';' { BGP_CFG->enable_hostname = $4; }
  | bgp_proto CAPABILITIES bool ';' { BGP_CFG->capabilities = $3; }
  | bgp_proto PASSWORD text ';' { BGP_CFG->password = $3; }
  | bgp_proto SETKEY bool ';' { BGP_CFG->setkey = $3; }

proto/bgp/packets.c

@@ -252,6 +252,14 @@ bgp_prepare_capabilities(struct bgp_conn *conn)
   if (p->cf->llgr_mode)
     caps->llgr_aware = 1;
 
+  if (p->cf->enable_hostname && config->hostname)
+  {
+    size_t length = strlen(config->hostname);
+    char *hostname = mb_allocz(p->p.pool, length+1);
+    memcpy(hostname, config->hostname, length+1);
+    caps->hostname = hostname;
+  }
+
   /* Allocate and fill per-AF fields */
   WALK_LIST(c, p->p.channels)
   {
@@ -412,6 +420,24 @@ bgp_write_capabilities(struct bgp_conn *conn, byte *buf)
     data[-1] = buf - data;
   }
 
+  if (caps->hostname)
+  {
+    *buf++ = 73;                /* Capability 73: Hostname */
+    *buf++ = 0;			/* Capability data length */
+    data = buf;
+
+    /* Hostname */
+    size_t length = strlen(caps->hostname);
+    *buf++ = length;
+    memcpy(buf, caps->hostname, length);
+    buf += length;
+
+    /* Domain, not implemented */
+    *buf++ = 0;
+
+    data[-1] = buf - data;
+  }
+
   caps->length = buf - buf_head;
 
   return buf;
@@ -573,6 +599,21 @@ bgp_read_capabilities(struct bgp_conn *conn, byte *pos, int len)
       }
       break;
 
+    case 73: /* Hostname, RFC draft */
+      if ((cl < 2) || (cl < 2 + pos[2]))
+        goto err;
+
+      int length = pos[2];
+      char *hostname = mb_allocz(p->p.pool, length+1);
+      memcpy(hostname, pos + 3, length);
+      hostname[length] = 0;
+
+      for (i = 0; i < length; i++)
+        if (hostname[i] < ' ')
+          hostname[i] = ' ';
+
+      caps->hostname = hostname;
+
       /* We can safely ignore all other capabilities */
     }