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-rw-r--r--doc/bird.sgml16
-rw-r--r--nest/a-path.c14
-rw-r--r--nest/attrs.h1
-rw-r--r--proto/bgp/attrs.c46
-rw-r--r--proto/bgp/config.Y2
5 files changed, 63 insertions, 16 deletions
diff --git a/doc/bird.sgml b/doc/bird.sgml
index 5ee9562..8fa55f8 100644
--- a/doc/bird.sgml
+++ b/doc/bird.sgml
@@ -784,7 +784,7 @@ for each neighbor using the following configuration parameters:
<tag>default bgp_med <m/number/</tag> Value of the Multiple Exit
Discriminator to be used during route selection when the MED attribute
- is missing. Default: infinite.
+ is missing. Default: 0.
<tag>default bgp_local_pref <m/number/</tag> Value of the Local Preference
to be used during route selection when the Local Preference attribute
@@ -806,10 +806,16 @@ with `<tt/O/') are optional.
selection among multiple BGP routes (see the selection rules above). It's
used as an additional metric which is propagated through the whole local AS.
- <tag>int <cf/bgp_med/ [IO]</tag> The Multiple Exit Discriminator of the route
- is an optional attribute which is often used within the local AS to
- reflect interior distances to various boundary routers. See the route selection
- rules above for exact semantics.
+ <tag>int <cf/bgp_med/ [O]</tag> The Multiple Exit Discriminator of the route
+ is an optional attribute which is used on on external (inter-AS) links to
+ convey to an adjacent AS the optimal entry point into the local AS.
+ The received attribute may be also propagated over internal BGP links
+ (and this is default behavior). The attribute value is zeroed when a route
+ is exported from a routing table to a BGP instance to ensure that the attribute
+ received from a neighboring AS is not propagated to other neighboring ASes.
+ A new value might be set in the export filter of a BGP instance.
+ See RFC 4451<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4451.txt">
+ for further discussion of BGP MED attribute.
<tag>enum <cf/bgp_origin/</tag> Origin of the route: either <cf/ORIGIN_IGP/
if the route has originated in an interior routing protocol or
diff --git a/nest/a-path.c b/nest/a-path.c
index f466691..5e3ecfd 100644
--- a/nest/a-path.c
+++ b/nest/a-path.c
@@ -244,6 +244,20 @@ as_path_get_first(struct adata *path, u32 *orig_as)
}
int
+as_path_get_last(struct adata *path, u32 *last_as)
+{
+ u8 *p = path->data;
+
+ if ((path->length == 0) || (p[0] != AS_PATH_SEQUENCE) || (p[1] == 0))
+ return 0;
+ else
+ {
+ *last_as = get_as(p+2);
+ return 1;
+ }
+}
+
+int
as_path_is_member(struct adata *path, u32 as)
{
int bs = bgp_as4_support ? 4 : 2;
diff --git a/nest/attrs.h b/nest/attrs.h
index aaa5f4a..fee2c2c 100644
--- a/nest/attrs.h
+++ b/nest/attrs.h
@@ -27,6 +27,7 @@ int as_path_convert_to_new(struct adata *path, byte *dst, int req_as);
void as_path_format(struct adata *path, byte *buf, unsigned int size);
int as_path_getlen(struct adata *path);
int as_path_get_first(struct adata *path, u32 *orig_as);
+int as_path_get_last(struct adata *path, u32 *last_as);
int as_path_is_member(struct adata *path, u32 as);
diff --git a/proto/bgp/attrs.c b/proto/bgp/attrs.c
index b5d8fba..2210cbe 100644
--- a/proto/bgp/attrs.c
+++ b/proto/bgp/attrs.c
@@ -146,7 +146,7 @@ static struct attr_desc bgp_attr_table[] = {
bgp_check_as_path, NULL },
{ "next_hop", 4, BAF_TRANSITIVE, EAF_TYPE_IP_ADDRESS, 1, /* BA_NEXT_HOP */
bgp_check_next_hop, NULL },
- { "med", 4, BAF_OPTIONAL, EAF_TYPE_INT, 0, /* BA_MULTI_EXIT_DISC */
+ { "med", 4, BAF_OPTIONAL, EAF_TYPE_INT, 1, /* BA_MULTI_EXIT_DISC */
NULL, NULL },
{ "local_pref", 4, BAF_TRANSITIVE, EAF_TYPE_INT, 0, /* BA_LOCAL_PREF */
NULL, NULL },
@@ -829,7 +829,17 @@ bgp_update_attrs(struct bgp_proto *p, rte *e, ea_list **attrs, struct linpool *p
eattr *a;
if (!p->is_internal)
- bgp_path_prepend(e, attrs, pool, p->local_as);
+ {
+ bgp_path_prepend(e, attrs, pool, p->local_as);
+
+ /* The MULTI_EXIT_DISC attribute received from a neighboring AS MUST NOT be
+ * propagated to other neighboring ASes.
+ * Perhaps it would be better to undefine it.
+ */
+ a = ea_find(e->attrs->eattrs, EA_CODE(EAP_BGP, BA_MULTI_EXIT_DISC));
+ if (a)
+ bgp_attach_attr(attrs, pool, BA_MULTI_EXIT_DISC, 0);
+ }
a = ea_find(e->attrs->eattrs, EA_CODE(EAP_BGP, BA_NEXT_HOP));
if (a && (p->is_internal || (!p->is_internal && e->attrs->iface == p->neigh->iface)))
@@ -894,6 +904,18 @@ bgp_import_control(struct proto *P, rte **new, ea_list **attrs, struct linpool *
return bgp_create_attrs(p, e, attrs, pool);
}
+static inline u32
+bgp_get_neighbor(rte *r)
+{
+ eattr *e = ea_find(r->attrs->eattrs, EA_CODE(EAP_BGP, BA_AS_PATH));
+ u32 as;
+
+ if (e && as_path_get_last(e->u.ptr, &as))
+ return as;
+ else
+ return ((struct bgp_proto *) r->attrs->proto)->remote_as;
+}
+
int
bgp_rte_better(rte *new, rte *old)
{
@@ -936,14 +958,18 @@ bgp_rte_better(rte *new, rte *old)
return 0;
/* RFC 4271 9.1.2.2. c) Compare MED's */
- x = ea_find(new->attrs->eattrs, EA_CODE(EAP_BGP, BA_MULTI_EXIT_DISC));
- y = ea_find(old->attrs->eattrs, EA_CODE(EAP_BGP, BA_MULTI_EXIT_DISC));
- n = x ? x->u.data : new_bgp->cf->default_med;
- o = y ? y->u.data : old_bgp->cf->default_med;
- if (n < o)
- return 1;
- if (n > o)
- return 0;
+
+ if (bgp_get_neighbor(new) == bgp_get_neighbor(old))
+ {
+ x = ea_find(new->attrs->eattrs, EA_CODE(EAP_BGP, BA_MULTI_EXIT_DISC));
+ y = ea_find(old->attrs->eattrs, EA_CODE(EAP_BGP, BA_MULTI_EXIT_DISC));
+ n = x ? x->u.data : new_bgp->cf->default_med;
+ o = y ? y->u.data : old_bgp->cf->default_med;
+ if (n < o)
+ return 1;
+ if (n > o)
+ return 0;
+ }
/* RFC 4271 9.1.2.2. d) Prefer external peers */
if (new_bgp->is_internal > old_bgp->is_internal)
diff --git a/proto/bgp/config.Y b/proto/bgp/config.Y
index d7bba57..8524b2d 100644
--- a/proto/bgp/config.Y
+++ b/proto/bgp/config.Y
@@ -33,7 +33,7 @@ bgp_proto_start: proto_start BGP {
BGP_CFG->hold_time = 240;
BGP_CFG->connect_retry_time = 120;
BGP_CFG->initial_hold_time = 240;
- BGP_CFG->default_med = ~0; /* RFC 1771 doesn't specify this, draft-09 says ~0 */
+ BGP_CFG->default_med = 0;
BGP_CFG->compare_path_lengths = 1;
BGP_CFG->start_delay_time = 5;
BGP_CFG->error_amnesia_time = 300;