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BGP: Add option to enforce first AS in AS_PATH

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This is optional check described in RFC 4271. Although this can be also
done by filters, it is widely implemented option in BGP implementations.

Thanks to Eugene Bogomazov for the original patch.
This commit is contained in:
Ondrej Zajicek (work)
2019-11-10 02:06:07 +01:00
parent becda5638a
commit 0b228fca04
5 changed files with 35 additions and 6 deletions
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24
proto/bgp/attrs.c
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@@ -404,6 +404,15 @@ bgp_format_origin(eattr *a, byte *buf, uint size UNUSED)
}
static inline int
bgp_as_path_first_as_equal(const byte *data, uint len, u32 asn)
{
return (len >= 6) &&
((data[0] == AS_PATH_SEQUENCE) || (data[0] == AS_PATH_CONFED_SEQUENCE)) &&
(data[1] > 0) &&
(get_u32(data+2) == asn);
}
static int
bgp_encode_as_path(struct bgp_write_state *s, eattr *a, byte *buf, uint size)
{
@@ -433,11 +442,6 @@ bgp_decode_as_path(struct bgp_parse_state *s, uint code UNUSED, uint flags, byte
if (!as_path_valid(data, len, as_length, as_sets, as_confed, err, sizeof(err)))
WITHDRAW("Malformed AS_PATH attribute - %s", err);
/* In some circumstances check for initial AS_CONFED_SEQUENCE; RFC 5065 5.0 */
if (p->is_interior && !p->is_internal &&
((len < 2) || (data[0] != AS_PATH_CONFED_SEQUENCE)))
WITHDRAW("Malformed AS_PATH attribute - %s", "missing initial AS_CONFED_SEQUENCE");
if (!s->as4_session)
{
/* Prepare 32-bit AS_PATH (from 16-bit one) in a temporary buffer */
@@ -446,6 +450,16 @@ bgp_decode_as_path(struct bgp_parse_state *s, uint code UNUSED, uint flags, byte
len = as_path_16to32(data, src, len);
}
/* In some circumstances check for initial AS_CONFED_SEQUENCE; RFC 5065 5.0 */
if (p->is_interior && !p->is_internal &&
((len < 2) || (data[0] != AS_PATH_CONFED_SEQUENCE)))
WITHDRAW("Malformed AS_PATH attribute - %s", "missing initial AS_CONFED_SEQUENCE");
/* Reject routes with first AS in AS_PATH not matching neighbor AS; RFC 4271 6.3 */
if (!p->is_internal && p->cf->enforce_first_as &&
!bgp_as_path_first_as_equal(data, len, p->remote_as))
WITHDRAW("Malformed AS_PATH attribute - %s", "First AS differs from neigbor AS");
bgp_set_attr_data(to, s->pool, BA_AS_PATH, flags, data, len);
}