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bgp: Support multiple labels in BGP-LU #19961

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3e5b23a
bgpd: Support multiple labels in BGP-LU
hedrok Oct 31, 2025
90af0a4
tests: add test for multiple labels in BGP-LU
hedrok Nov 2, 2025
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17 changes: 10 additions & 7 deletions bgpd/bgp_attr.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3582,7 +3582,7 @@ bgp_attr_pmsi_tunnel(struct bgp_attr_parser_args *args)
struct attr *const attr = args->attr;
const bgp_size_t length = args->length;
uint8_t tnl_type;
int attr_parse_len = 2 + BGP_LABEL_BYTES;
int attr_parse_len = 2 + MPLS_LABEL_LEN_BYTES;

if (peer->discard_attrs[args->type] || peer->withdraw_attrs[args->type])
goto pmsi_tunnel_ignore;
Expand Down Expand Up @@ -3617,7 +3617,7 @@ bgp_attr_pmsi_tunnel(struct bgp_attr_parser_args *args)

bgp_attr_set(attr, BGP_ATTR_PMSI_TUNNEL);
bgp_attr_set_pmsi_tnl_type(attr, tnl_type);
stream_get(&attr->label, connection->curr, BGP_LABEL_BYTES);
stream_get(&attr->label, connection->curr, MPLS_LABEL_LEN_BYTES);

/* Forward read pointer of input stream. */
stream_forward_getp(connection->curr, length - attr_parse_len);
Expand Down Expand Up @@ -4752,7 +4752,7 @@ void bgp_packet_mpattr_prefix(struct stream *s, afi_t afi, safi_t safi,
stream_putl(s, addpath_tx_id);
/* Label, RD, Prefix write. */
stream_putc(s, p->prefixlen + 88);
stream_put(s, label, BGP_LABEL_BYTES);
stream_put(s, label, MPLS_LABEL_LEN_BYTES);
stream_put(s, prd->val, 8);
stream_put(s, &p->u.prefix, PSIZE(p->prefixlen));
break;
Expand All @@ -4767,8 +4767,7 @@ void bgp_packet_mpattr_prefix(struct stream *s, afi_t afi, safi_t safi,
break;
case SAFI_LABELED_UNICAST:
/* Prefix write with label. */
stream_put_labeled_prefix(s, p, label, addpath_capable,
addpath_tx_id);
stream_put_labeled_prefix(s, p, label, num_labels, addpath_capable, addpath_tx_id);
break;
case SAFI_FLOWSPEC:
stream_putc(s, p->u.prefix_flowspec.prefixlen);
Expand Down Expand Up @@ -4807,7 +4806,11 @@ size_t bgp_packet_mpattr_prefix_size(afi_t afi, safi_t safi,
assert(!"Do we try to use this?");
break;
case SAFI_LABELED_UNICAST:
size += BGP_LABEL_BYTES;
/*
* Length of all labels + prefix is given in bits in one octet,
* so maximum 256 bits, 32 bytes
*/
size += 32 - PSIZE(p->prefixlen);
break;
case SAFI_EVPN:
/*
Expand Down Expand Up @@ -5431,7 +5434,7 @@ bgp_size_t bgp_packet_attribute(struct bgp *bgp, struct peer *peer, struct strea
stream_putc(s, 0); // Flags
stream_putc(s, bgp_attr_get_pmsi_tnl_type(attr));
stream_put(s, &(attr->label),
BGP_LABEL_BYTES); // MPLS Label / VXLAN VNI
MPLS_LABEL_LEN_BYTES); // MPLS Label / VXLAN VNI
stream_put_ipv4(s, attr->nexthop.s_addr);
// Unicast tunnel endpoint IP address
}
Expand Down
6 changes: 1 addition & 5 deletions bgpd/bgp_debug.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2965,11 +2965,7 @@ const char *bgp_debug_rdpfxpath2str(afi_t afi, safi_t safi,
snprintf(tag_buf, sizeof(tag_buf), " label %s",
tag_buf2);
} else {
uint32_t label_value;

label_value = decode_label(label);
snprintf(tag_buf, sizeof(tag_buf), " label %u",
label_value);
mpls_labels2str(label, num_labels, " label ", tag_buf, sizeof(tag_buf));
}
}

Expand Down
16 changes: 8 additions & 8 deletions bgpd/bgp_evpn.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4988,13 +4988,13 @@ static int process_type2_route(struct peer *peer, afi_t afi, safi_t safi,
}

/* Get the VNI(s). Stored as bytes here. */
STREAM_GET(&label[0], pkt, BGP_LABEL_BYTES);
STREAM_GET(&label[0], pkt, MPLS_LABEL_LEN_BYTES);
num_labels++;

/* Do we have a second VNI? */
if (STREAM_READABLE(pkt)) {
num_labels++;
STREAM_GET(&label[1], pkt, BGP_LABEL_BYTES);
STREAM_GET(&label[1], pkt, MPLS_LABEL_LEN_BYTES);
}

/* Process the route. */
Expand Down Expand Up @@ -5187,11 +5187,11 @@ static int process_type5_route(struct peer *peer, afi_t afi, safi_t safi,

/* Get the VNI (in MPLS label field). Stored as bytes here. */
memset(&label, 0, sizeof(label));
memcpy(&label, pfx, BGP_LABEL_BYTES);
memcpy(&label, pfx, MPLS_LABEL_LEN_BYTES);

/*
* If in future, we are required to access additional fields,
* we MUST increment pfx by BGP_LABEL_BYTES in before reading the next
* we MUST increment pfx by MPLS_LABEL_LEN_BYTES in before reading the next
* field
*/

Expand Down Expand Up @@ -6157,10 +6157,10 @@ void bgp_evpn_encode_prefix(struct stream *s, const struct prefix *p,
stream_put(s, &evp->prefix.macip_addr.ip.ip.addr,
ipa_len);
/* 1st label is the L2 VNI */
stream_put(s, label, BGP_LABEL_BYTES);
stream_put(s, label, MPLS_LABEL_LEN_BYTES);
/* Include 2nd label (L3 VNI) if advertising MAC+IP */
if (ipa_len && num_labels > 1)
stream_put(s, label + 1, BGP_LABEL_BYTES);
stream_put(s, label + 1, MPLS_LABEL_LEN_BYTES);
break;

case BGP_EVPN_IMET_ROUTE:
Expand Down Expand Up @@ -6198,12 +6198,12 @@ void bgp_evpn_encode_prefix(struct stream *s, const struct prefix *p,

case BGP_EVPN_AD_ROUTE:
/* RD, ESI, EthTag, 1 VNI */
len = RD_BYTES + ESI_BYTES + EVPN_ETH_TAG_BYTES + BGP_LABEL_BYTES;
len = RD_BYTES + ESI_BYTES + EVPN_ETH_TAG_BYTES + MPLS_LABEL_LEN_BYTES;
stream_putc(s, len);
stream_put(s, prd->val, RD_BYTES); /* RD */
stream_put(s, evp->prefix.ead_addr.esi.val, ESI_BYTES); /* ESI */
stream_putl(s, evp->prefix.ead_addr.eth_tag); /* Ethernet Tag */
stream_put(s, label, BGP_LABEL_BYTES);
stream_put(s, label, MPLS_LABEL_LEN_BYTES);
break;

case BGP_EVPN_IP_PREFIX_ROUTE:
Expand Down
2 changes: 1 addition & 1 deletion bgpd/bgp_evpn_mh.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1228,7 +1228,7 @@ int bgp_evpn_type1_route_process(struct peer *peer, afi_t afi, safi_t safi,
eth_tag = ntohl(eth_tag);
pfx += EVPN_ETH_TAG_BYTES;

memcpy(&label[0], pfx, BGP_LABEL_BYTES);
memcpy(&label[0], pfx, MPLS_LABEL_LEN_BYTES);

/* EAD route prefix doesn't include the nexthop in the global
* table
Expand Down
124 changes: 89 additions & 35 deletions bgpd/bgp_label.c
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Original file line number Diff line number Diff line change
Expand Up @@ -198,32 +198,40 @@ int bgp_parse_fec_update(void)
return 1;
}

mpls_label_t bgp_adv_label(struct bgp_dest *dest, struct bgp_path_info *pi,
struct peer *to, afi_t afi, safi_t safi)
void bgp_adv_label(struct bgp_dest *dest, struct bgp_path_info *pi, struct peer *to, afi_t afi,
safi_t safi, mpls_label_t *labels, uint8_t *num_labels)
{
struct peer *from;
mpls_label_t remote_label;
int reflect;
uint8_t i;
bool use_local_label = true;

if (!dest || !pi || !to)
return MPLS_INVALID_LABEL;
labels[0] = MPLS_INVALID_LABEL;
if (!dest || !pi || !to) {
*num_labels = 0;
return;
}

remote_label = BGP_PATH_INFO_NUM_LABELS(pi)
? pi->extra->labels->label[0]
: MPLS_INVALID_LABEL;
from = pi->peer;
reflect =
((from->sort == BGP_PEER_IBGP) && (to->sort == BGP_PEER_IBGP));

if (reflect
&& !CHECK_FLAG(to->af_flags[afi][safi],
PEER_FLAG_FORCE_NEXTHOP_SELF))
return remote_label;
use_local_label = false;

if (CHECK_FLAG(to->af_flags[afi][safi], PEER_FLAG_NEXTHOP_UNCHANGED))
return remote_label;
use_local_label = false;

return dest->local_label;
if (use_local_label) {
*num_labels = 1;
labels[0] = dest->local_label;
} else {
*num_labels = BGP_PATH_INFO_NUM_LABELS(pi);
for (i = 0; i < *num_labels; i++)
labels[i] = pi->extra->labels->label[i];
}
}

static void bgp_send_fec_register_label_msg(struct bgp_dest *dest, bool reg,
Expand Down Expand Up @@ -413,35 +421,50 @@ void bgp_reg_dereg_for_label(struct bgp_dest *dest, struct bgp_path_info *pi,
dest, reg, with_label_index ? pi->attr->label_index : 0);
}

static int bgp_nlri_get_labels(struct peer *peer, uint8_t *pnt, uint8_t plen,
mpls_label_t *label)
/* Labels must have BGP_MAX_LABELS elements */
static int bgp_nlri_get_labels(struct peer *peer, uint8_t *pnt, uint8_t plen, mpls_label_t *labels,
uint8_t *num_labels)
{
uint8_t *data = pnt;
uint8_t *lim = pnt + plen;
uint8_t llen = 0;
uint8_t label_depth = 0;
mpls_label_t *label_pnt;
mpls_label_t label;

if (plen < BGP_LABEL_BYTES)
if (plen < MPLS_LABEL_LEN_BYTES)
return 0;

for (; data < lim; data += BGP_LABEL_BYTES) {
memcpy(label, data, BGP_LABEL_BYTES);
llen += BGP_LABEL_BYTES;
label_pnt = &labels[0];
for (; data < lim; data += MPLS_LABEL_LEN_BYTES, label_pnt++) {
/*
* Support only BGP_MAX_LABELS, read rest to local variable and
* discard, shouldn't be possible - see comment to BGP_MAX_LABELS
*/
if (label_depth >= BGP_MAX_LABELS)
label_pnt = &label;

memcpy(label_pnt, data, MPLS_LABEL_LEN_BYTES);
llen += MPLS_LABEL_LEN_BYTES;

bgp_set_valid_label(label_pnt);

bgp_set_valid_label(label);
label_depth += 1;

if (bgp_is_withdraw_label(label) || label_bos(label))
if (bgp_is_withdraw_label(label_pnt) || label_bos(label_pnt))
break;
}

/* If we RX multiple labels we will end up keeping only the last
* one. We do not yet support a label stack greater than 1. */
if (label_depth > 1)
zlog_info("%pBP rcvd UPDATE with label stack %d deep", peer,
label_depth);
*num_labels = label_depth;

if (label_depth > BGP_MAX_LABELS) {
*num_labels = BGP_MAX_LABELS;
label_set_bos(&labels[*num_labels - 1]);
zlog_info("%pBP rcvd UPDATE with label stack %d deep, using only first %d labels",
peer, label_depth, BGP_MAX_LABELS);
}

if (!(bgp_is_withdraw_label(label) || label_bos(label)))
if (!(bgp_is_withdraw_label(label_pnt) || label_bos(label_pnt)))
flog_warn(
EC_BGP_INVALID_LABEL_STACK,
"%pBP rcvd UPDATE with invalid label stack - no bottom of stack",
Expand All @@ -462,7 +485,8 @@ int bgp_nlri_parse_label(struct peer *peer, struct attr *attr,
safi_t safi;
bool addpath_capable;
uint32_t addpath_id;
mpls_label_t label = MPLS_INVALID_LABEL;
mpls_label_t labels[MPLS_MAX_LABELS] = { MPLS_INVALID_LABEL };
uint8_t num_labels = 0;
uint8_t llen;

pnt = packet->nlri;
Expand Down Expand Up @@ -506,7 +530,7 @@ int bgp_nlri_parse_label(struct peer *peer, struct attr *attr,
}

/* Fill in the labels */
llen = bgp_nlri_get_labels(peer, pnt, psize, &label);
llen = bgp_nlri_get_labels(peer, pnt, psize, labels, &num_labels);
if (llen == 0) {
flog_err(
EC_BGP_UPDATE_RCV,
Expand Down Expand Up @@ -573,13 +597,11 @@ int bgp_nlri_parse_label(struct peer *peer, struct attr *attr,
}

if (attr) {
bgp_update(peer, &p, addpath_id, attr, packet->afi,
safi, ZEBRA_ROUTE_BGP, BGP_ROUTE_NORMAL,
NULL, &label, 1, 0, NULL);
bgp_update(peer, &p, addpath_id, attr, packet->afi, safi, ZEBRA_ROUTE_BGP,
BGP_ROUTE_NORMAL, NULL, labels, num_labels, 0, NULL);
} else {
bgp_withdraw(peer, &p, addpath_id, packet->afi,
SAFI_UNICAST, ZEBRA_ROUTE_BGP,
BGP_ROUTE_NORMAL, NULL, &label, 1);
bgp_withdraw(peer, &p, addpath_id, packet->afi, SAFI_UNICAST,
ZEBRA_ROUTE_BGP, BGP_ROUTE_NORMAL, NULL, labels, num_labels);
}
}

Expand All @@ -606,7 +628,7 @@ uint32_t decode_label(mpls_label_t *label_pnt)
return l;
}

void encode_label(mpls_label_t label, mpls_label_t *label_pnt)
void encode_label_bos(mpls_label_t label, mpls_label_t *label_pnt, bool bos)
{
uint8_t *pnt = (uint8_t *)label_pnt;

Expand All @@ -618,7 +640,12 @@ void encode_label(mpls_label_t label, mpls_label_t *label_pnt)
}
*pnt++ = (label >> 12) & 0xff;
*pnt++ = (label >> 4) & 0xff;
*pnt++ = ((label << 4) + 1) & 0xff; /* S=1 */
*pnt++ = ((label << 4) + (bos ? 1 : 0)) & 0xff;
}

void encode_label(mpls_label_t label, mpls_label_t *label_pnt)
{
encode_label_bos(label, label_pnt, true);
}

bool bgp_labels_same(const mpls_label_t *tbl_a, const uint8_t num_labels_a,
Expand Down Expand Up @@ -646,3 +673,30 @@ bool bgp_labels_is_implicit_null(struct bgp_path_info *pi)
return true;
return false;
}

char *mpls_labels2str(mpls_label_t *labels, uint8_t num_labels, const char *prefix, char *buf,
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@ritika0313 ritika0313 Nov 7, 2025

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Please check if we can reuse the existing function - mpls_label2str() from lib/mpls.c

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@hedrok hedrok Nov 8, 2025

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Unfortunately can't just reuse it - it doesn't decode labels, just outputs as integers:

		if (pretty)
			label2str(labels[i], type, label_buf,
				  sizeof(label_buf));
		else
			snprintf(label_buf, sizeof(label_buf), "%u",
				 ((type == ZEBRA_LSP_EVPN)
					  ? label2vni(&labels[i])
					  : labels[i]));

label2str does the same - just outputs label as integer or label2vni in EVPN case.

Theoretically they could have been merged, but pairs of functions decode_label/mpls_lse_decode etc hint that somewhy they are not merged. Probably it would be a good refactoring but I don't think it is a good idea to include that in this task.

int size)
{
uint32_t label_value;
uint32_t len = 0;
uint8_t i;

buf[0] = '\0';
if (!num_labels)
return buf;

if (prefix) {
strlcat(buf + len, prefix, size - len);
len = strlen(buf);
}

label_value = decode_label(&labels[0]);
len += snprintf(buf + len, size - len, "%u", label_value);

for (i = 1; i < num_labels; i++) {
label_value = decode_label(&labels[i]);
len += snprintf(buf + len, size - len, "/%u", label_value);
}

return buf;
}
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