diff options
| -rw-r--r-- | doc/bird.sgml | 16 | ||||
| -rw-r--r-- | nest/a-path.c | 14 | ||||
| -rw-r--r-- | nest/attrs.h | 1 | ||||
| -rw-r--r-- | proto/bgp/attrs.c | 46 | ||||
| -rw-r--r-- | proto/bgp/config.Y | 2 |
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; |