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BGP: Allow exchanging LOCAL_PREF with eBGP peers
Adds option 'allow bgp_local_pref' to override the usual restriction of LOCAL_PREF on eBGP sessions. Thanks to Lennert Buytenhek for the patch.
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@ -2043,6 +2043,14 @@ using the following configuration parameters:
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TX direction. When active, all available routes accepted by the export
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filter are advertised to the neighbor. Default: off.
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<tag><label id="bgp-allow-local-pref">allow bgp_local_pref <m/switch/</tag>
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A standard BGP implementation do not send the Local Preference attribute
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to eBGP neighbors and ignore this attribute if received from eBGP
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neighbors, as per <rfc id="4271">. When this option is enabled on an
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eBGP session, this attribute will be sent to and accepted from the peer,
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which is useful for example if you have a setup like in <rfc id="7938">.
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The option does not affect iBGP sessions. Default: off.
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<tag><label id="bgp-allow-local-as">allow local as [<m/number/]</tag>
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BGP prevents routing loops by rejecting received routes with the local
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AS number in the AS path. This option allows to loose or disable the
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@ -306,7 +306,7 @@ static struct attr_desc bgp_attr_table[] = {
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bgp_check_next_hop, bgp_format_next_hop },
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{ "med", 4, BAF_OPTIONAL, EAF_TYPE_INT, 1, /* BA_MULTI_EXIT_DISC */
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NULL, NULL },
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{ "local_pref", 4, BAF_TRANSITIVE, EAF_TYPE_INT, 0, /* BA_LOCAL_PREF */
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{ "local_pref", 4, BAF_TRANSITIVE, EAF_TYPE_INT, 1, /* BA_LOCAL_PREF */
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NULL, NULL },
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{ "atomic_aggr", 0, BAF_TRANSITIVE, EAF_TYPE_OPAQUE, 1, /* BA_ATOMIC_AGGR */
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NULL, NULL },
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@ -821,8 +821,13 @@ bgp_get_bucket(struct bgp_proto *p, net *n, ea_list *attrs, int originate)
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code = EA_ID(a->id);
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if (ATTR_KNOWN(code))
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{
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if (!bgp_attr_table[code].allow_in_ebgp && !p->is_internal)
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continue;
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if (!p->is_internal)
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{
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if (!bgp_attr_table[code].allow_in_ebgp)
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continue;
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if ((code == BA_LOCAL_PREF) && !p->cf->allow_local_pref)
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continue;
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}
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/* The flags might have been zero if the attr was added by filters */
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a->flags = (a->flags & BAF_PARTIAL) | bgp_attr_table[code].expected_flags;
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if (code < 32)
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@ -1776,8 +1781,13 @@ bgp_decode_attrs(struct bgp_conn *conn, byte *attr, uint len, struct linpool *po
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{ errcode = 5; goto err; }
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if ((desc->expected_flags ^ flags) & (BAF_OPTIONAL | BAF_TRANSITIVE))
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{ errcode = 4; goto err; }
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if (!desc->allow_in_ebgp && !bgp->is_internal)
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continue;
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if (!bgp->is_internal)
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{
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if (!desc->allow_in_ebgp)
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continue;
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if ((code == BA_LOCAL_PREF) && !bgp->cf->allow_local_pref)
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continue;
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}
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if (desc->validate)
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{
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errcode = desc->validate(bgp, z, l);
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@ -50,6 +50,7 @@ struct bgp_config {
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int secondary; /* Accept also non-best routes (i.e. RA_ACCEPTED) */
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int add_path; /* Use ADD-PATH extension [RFC7911] */
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int allow_local_as; /* Allow that number of local ASNs in incoming AS_PATHs */
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int allow_local_pref; /* Allow LOCAL_PREF in EBGP sessions */
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int gr_mode; /* Graceful restart mode (BGP_GR_*) */
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int setkey; /* Set MD5 password to system SA/SP database */
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unsigned gr_time; /* Graceful restart timeout */
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@ -126,6 +126,7 @@ bgp_proto:
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| bgp_proto ADD PATHS RX ';' { BGP_CFG->add_path = ADD_PATH_RX; }
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| bgp_proto ADD PATHS TX ';' { BGP_CFG->add_path = ADD_PATH_TX; }
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| bgp_proto ADD PATHS bool ';' { BGP_CFG->add_path = $4 ? ADD_PATH_FULL : 0; }
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| bgp_proto ALLOW BGP_LOCAL_PREF bool ';' { BGP_CFG->allow_local_pref = $4; }
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| bgp_proto ALLOW LOCAL AS ';' { BGP_CFG->allow_local_as = -1; }
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| bgp_proto ALLOW LOCAL AS expr ';' { BGP_CFG->allow_local_as = $5; }
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| bgp_proto GRACEFUL RESTART bool ';' { BGP_CFG->gr_mode = $4; }
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