Implement as path prepends. At least one prepend is needed for ebgp

neighbors. Fix a bug in the update generation. If no path attributes are
available e.g. a packet with only withdraws we need to set (and write) the
bgp path attribute field to zero. With this change we are able to send
valid updates to our neighbors with one exception: the nexthop field which
needs to be changed for ebgp neighbors.
OK henning@

4 files changed, 116 insertions, 18 deletions

diff --git a/usr.sbin/bgpd/rde.c b/usr.sbin/bgpd/rde.c
index 84614366952..09470f5dce2 100644
--- a/usr.sbin/bgpd/rde.c
+++ b/usr.sbin/bgpd/rde.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: rde.c,v 1.51 2004/01/10 16:20:29 claudio Exp $ */
+/*	$OpenBSD: rde.c,v 1.52 2004/01/10 22:25:42 claudio Exp $ */
 
 /*
  * Copyright (c) 2003, 2004 Henning Brauer <henning@openbsd.org>
@@ -618,8 +618,17 @@ rde_send_nexthop(in_addr_t next, int valid)
 		fatal("imsg_compose error");
 }
 
+/*
+ * update specific functions
+ */
 u_char	queue_buf[4096];
 
+u_int16_t
+rde_local_as(void)
+{
+	return conf->as;
+}
+
 void
 rde_update_queue_runner(void)
 {
@@ -634,10 +643,11 @@ rde_update_queue_runner(void)
 			if (peer->state != PEER_UP)
 				continue;
 			/* first withdraws */
-			wpos = 2;
-			r = up_dump_prefix(queue_buf + wpos, len - wpos,
+			wpos = 2; /* reserve space for the lenght field */
+			r = up_dump_prefix(queue_buf + wpos, len - wpos - 2,
 			    &peer->withdraws, peer);
 			wd_len = r;
+			/* write withdraws lenght filed */
 			wd_len = htons(wd_len);
 			memcpy(queue_buf, &wd_len, 2);
 			wpos += r;
@@ -647,8 +657,11 @@ rde_update_queue_runner(void)
 			    peer);
 			wpos += r;
 
-			if (wpos == 2)
-				/* no packet to send */
+			if (wpos == 4)
+				/*
+				 * No packet to send. The 4 bytes are the
+				 * needed withdraw and path attribute lenght.
+				 */
 				continue;
 
 			/* finally send message to SE */
diff --git a/usr.sbin/bgpd/rde.h b/usr.sbin/bgpd/rde.h
index b151c31553b..b0110dd2c88 100644
--- a/usr.sbin/bgpd/rde.h
+++ b/usr.sbin/bgpd/rde.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: rde.h,v 1.12 2004/01/10 16:20:29 claudio Exp $ */
+/*	$OpenBSD: rde.h,v 1.13 2004/01/10 22:25:42 claudio Exp $ */
 
 /*
  * Copyright (c) 2003, 2004 Claudio Jeker <claudio@openbsd.org> and
@@ -218,6 +218,7 @@ struct prefix {
 /* rde.c */
 void		 rde_send_kroute(struct prefix *, struct prefix *);
 void		 rde_send_nexthop(in_addr_t, int);
+u_int16_t	 rde_local_as(void);
 
 /* rde_rib.c */
 int		 attr_compare(struct attr_flags *, struct attr_flags *);
@@ -233,6 +234,8 @@ int		 aspath_verify(void *, u_int16_t, u_int16_t);
 #define		 AS_ERR_LOOP	-3
 struct aspath	*aspath_create(void *, u_int16_t);
 void		 aspath_destroy(struct aspath *);
+int		 aspath_write(void *, u_int16_t, struct aspath *, u_int16_t,
+		     int);
 u_char		*aspath_dump(struct aspath *);
 u_int16_t	 aspath_length(struct aspath *);
 u_int16_t	 aspath_count(struct aspath *);
diff --git a/usr.sbin/bgpd/rde_decide.c b/usr.sbin/bgpd/rde_decide.c
index 4e66e58515b..08c18bc3bac 100644
--- a/usr.sbin/bgpd/rde_decide.c
+++ b/usr.sbin/bgpd/rde_decide.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: rde_decide.c,v 1.12 2004/01/10 16:20:29 claudio Exp $ */
+/*	$OpenBSD: rde_decide.c,v 1.13 2004/01/10 22:25:42 claudio Exp $ */
 
 /*
  * Copyright (c) 2003, 2004 Claudio Jeker <claudio@openbsd.org>
@@ -475,7 +475,7 @@ up_generate_attr(struct rde_peer *peer, struct update_attr *upa,
 	struct attr	*oa;
 	u_int32_t	 tmp32;
 	int		 r;
-	u_int16_t	 aslen, len = sizeof(up_attr_buf), wlen = 0;
+	u_int16_t	 len = sizeof(up_attr_buf), wlen = 0;
 
 	/* origin */
 	if ((r = attr_write(up_attr_buf + wlen, len, ATTR_WELL_KNOWN,
@@ -484,10 +484,8 @@ up_generate_attr(struct rde_peer *peer, struct update_attr *upa,
 	wlen += r; len -= r;
 
 	/* aspath */
-	/* XXX XXX aspath prepends */
-	aslen = aspath_length(a->aspath);
-	if ((r = attr_write(up_attr_buf + wlen, len, ATTR_WELL_KNOWN,
-	    ATTR_ASPATH, aspath_dump(a->aspath), aslen)) == -1)
+	if ((r = aspath_write(up_attr_buf + wlen, len, a->aspath,
+	    rde_local_as(), peer->conf.ebgp == 0 ? 0 : 1)) == -1)
 		return (-1);
 	wlen += r; len -= r;
 
@@ -613,18 +611,26 @@ up_dump_attrnlri(u_char *buf, int len, struct rde_peer *peer)
 	u_int16_t		 attr_len;
 
 	upa = TAILQ_FIRST(&peer->updates);
-	if (upa == NULL || upa->attr_len + 5 > len) 
-		/* either no packet or not enough space */
-		return (0);
+	if (upa == NULL || upa->attr_len + 5 > len) {
+		/*
+		 * either no packet or not enough space.
+		 * The length field needs to be set to zero else it would be
+		 * an invalid bgp update.
+		 */
+		bzero(buf, 2);
+		return (2);
+	}
 
-	/* first dump the attributes */
+	/* first dump the 2-byte path attribute length */
 	attr_len = htons(upa->attr_len);
 	memcpy(buf, &attr_len, 2);
 	wpos = 2;
+
+	/* then the path attributes them self */
 	memcpy(buf + wpos, upa->attr, upa->attr_len);
 	wpos += upa->attr_len;
 
-	/* now dump the nlri */
+	/* last but not least dump the nlri */
 	r = up_dump_prefix(buf + wpos, len - wpos, &upa->prefix_h, peer);
 	wpos += r;
 
diff --git a/usr.sbin/bgpd/rde_rib.c b/usr.sbin/bgpd/rde_rib.c
index 097d18e02e6..f4712ffef3b 100644
--- a/usr.sbin/bgpd/rde_rib.c
+++ b/usr.sbin/bgpd/rde_rib.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: rde_rib.c,v 1.15 2004/01/10 16:20:29 claudio Exp $ */
+/*	$OpenBSD: rde_rib.c,v 1.16 2004/01/10 22:25:42 claudio Exp $ */
 
 /*
  * Copyright (c) 2003, 2004 Claudio Jeker <claudio@openbsd.org>
@@ -297,6 +297,82 @@ aspath_create(void *data, u_int16_t len)
 	return aspath;
 }
 
+int
+aspath_write(void *p, u_int16_t len, struct aspath *aspath, u_int16_t myAS,
+    int prepend)
+{
+	u_char		*b = p;
+	int		 tot_len, as_len, size, wpos = 0;
+	u_int16_t	 tmp;
+	u_int8_t	 type, attr_flag = ATTR_WELL_KNOWN;
+
+	if (prepend > 255)
+		/* lunatic prepends need to be blocked in the parser */
+		return (-1);
+
+	/* first calculate new size */
+	type = aspath->data[0];
+	size = aspath->data[1];
+	if (prepend == 0)
+		as_len = aspath->hdr.len;
+	else if (type == AS_SET || size + prepend > 255)
+		/* need to attach a new AS_SEQUENCE */
+		as_len = 2 + prepend * 2 + aspath->hdr.len;
+	else
+		as_len = prepend * 2 + aspath->hdr.len;
+
+	/* check buffer size */
+	tot_len = 2 + as_len;
+	if (as_len > 255) {
+		attr_flag |= ATTR_EXTLEN;
+		tot_len += 2;
+	} else
+		tot_len += 1;
+
+	if (tot_len > len)
+		return (-1);
+
+	/* header */
+	b[wpos++] = attr_flag;
+	b[wpos++] = ATTR_ASPATH;
+	if (as_len > 0xff) {
+		tmp = as_len;
+		tmp = htons(tmp);
+		memcpy(b, &tmp, 2);
+		wpos += 2;
+	} else
+		b[wpos++] = (u_char)(as_len & 0xff);
+
+	/* first prepends */
+	myAS = htons(myAS);
+	if (type == AS_SET) {
+		b[wpos++] = AS_SEQUENCE;
+		b[wpos++] = prepend;
+		for (; prepend > 0; prepend--) {
+			memcpy(b + wpos, &myAS, 2);
+			wpos += 2;
+		}
+		memcpy(b + wpos, aspath->data, aspath->hdr.len);
+	} else {
+		if (size + prepend > 255) {
+			b[wpos++] = AS_SEQUENCE;
+			b[wpos++] = size + prepend - 255;
+			for (; prepend + size > 255; prepend--) {
+				memcpy(b + wpos, &myAS, 2);
+				wpos += 2;
+			}
+		}
+		b[wpos++] = AS_SEQUENCE;
+		b[wpos++] = size + prepend;
+		for (; prepend > 0; prepend--) {
+			memcpy(b + wpos, &myAS, 2);
+			wpos += 2;
+		}
+		memcpy(b + wpos, aspath->data + 2, aspath->hdr.len - 2);
+	}
+	return (tot_len);
+}
+
 void
 aspath_destroy(struct aspath *aspath)
 {