* [PATCH v5 1/2] dhcpv6: Add --dhcpv6-opt with option type table and value parser
2026-10-29 18:13 [PATCH v5 0/2] [PATCH 0/2] dhcpv6: Add --dhcpv6-opt for custom DHCPv6 options Anshu Kumari
@ 2026-10-29 18:13 ` Anshu Kumari
2026-10-29 18:13 ` [PATCH v5 2/2] dhcpv6: Inject custom options into DHCPv6 replies Anshu Kumari
1 sibling, 0 replies; 3+ messages in thread
From: Anshu Kumari @ 2026-10-29 18:13 UTC (permalink / raw)
To: sbrivio, passt-dev; +Cc: lvivier, anskuma
Introduce the --dhcpv6-opt flag that allows setting arbitrary DHCPv6
options from command-line in the form [--dhcpv6-opt CODE,VALUE].
Add a type lookup table mapping option codes to value types (IPv6,
IPv6 list, integer, string, vendor class, length-prefixed string
list) and dhcpv6_opt_parse() to convert CLI strings to binary wire
format. If the same option code is given more than once, the
last value wins.
Link: https://bugs.passt.top/show_bug.cgi?id=192
Signed-off-by: Anshu Kumari <anskuma@redhat.com>
---
v5:
- Replaced optbuf[512] with optbuf[INANY_ADDRSTRLEN * 2]
- Added offset-based loop for dhcpv6_opt_to_str() to
paginate long IPv6 lists
- Renamed array dhcpv6_opt_types → dhcpv6_opt, renamed
function dhcpv6_opt() → dhcpv6_get_opt() to avoid naming conflict
- Updated RFC references from 8415 to 9915
v4:
- The dhcpv6_opt_code < 1 check was replaced with proper validation:
dhcpv6_opt_code == 0 || dhcpv6_opt_code > UINT16_MAX in conf.c
- All uint16_t/uint32_t writes to byte buffers now use intermediate
variables + memcpy() instead of direct pointer casts.
- The DHCPV6_OPT_STR case now uses slen > buf_len instead of slen >= buf_len.
- Option 17 (Vendor-specific Info) excluded.
- A separate char optbuf[512] was added in conf_print() instead of
reusing the small INANY_ADDRSTRLEN-sized buf for option rendering.
- inet_ntop() return value checked.
- Uses off += strlen(buf + off) instead of off = strlen(buf) in
the IPv6 list rendering loop.
- Iterator macro added — for_each_in6_off(off, len).
- The addr and af variables are declared at function scope
in dhcpv6_opt_parse() rather than inside block wrappers.
- snprintf() alignment and line formatting.
v3:
- Use parse_unsigned(), parse_literal(), parse_eoi() from parse.c
instead of manual strtoul()/errno/strchr() in dhcpv6_opt_parse()
for UINT and VENDOR_CLASS cases.
- Store options as pre-parsed binary in a static array indexed by
option code, instead of storing raw strings.
- Add dhcpv6_opt_to_str() to render binary option values back to
printable strings for startup logging in conf_print().
v2:
- Renamed custom_v6opts to dhcpv6_opts, MAX_CUSTOM_DHCPV6_OPTS
to MAX_DHCPV6_OPTS.
- Dropped val/len from ctx struct.
- Moved dhcpv6_add_option() to conf.c as static
conf_dhcpv6_option().
- Made dhcpv6_opt_parse() non-static, declared in dhcpv6.h
- Omitted explicit [256] from dhcpv6_opt_types[].
- Moved chunk declaration into while block.
- Removed redundant !slen check in DHCPV6_OPT_STR case.
- All errors in dhcpv6_opt_parse() return -1, removed die()
calls.
---
conf.c | 27 +++-
dhcpv6.c | 369 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
dhcpv6.h | 3 +
passt.1 | 31 +++++
4 files changed, 420 insertions(+), 10 deletions(-)
diff --git a/conf.c b/conf.c
index 149a4c79..6607add1 100644
--- a/conf.c
+++ b/conf.c
@@ -47,6 +47,7 @@
#include "lineread.h"
#include "isolation.h"
#include "log.h"
+#include "dhcpv6.h"
#include "vhost_user.h"
#include "epoll_ctl.h"
#include "conf.h"
@@ -632,7 +633,8 @@ static void usage(const char *name, FILE *f, int status)
" -S, --search LIST Space-separated list, search domains\n"
" a single, empty option disables the DNS search list\n"
" -H, --hostname NAME Hostname to configure client with\n"
- " --fqdn NAME FQDN to configure client with\n");
+ " --fqdn NAME FQDN to configure client with\n"
+ " --dhcpv6-opt CODE,VAL Set DHCPv6 option CODE to VAL\n");
if (strstr(name, "pasta"))
FPRINTF(f, " default: don't use any search list\n");
else
@@ -800,6 +802,7 @@ enum passt_modes conf_mode(int argc, char *argv[])
*/
static void conf_print(const struct ctx *c)
{
+ char optbuf[INANY_ADDRSTRLEN * 2];
char buf[INANY_ADDRSTRLEN];
int i;
@@ -901,6 +904,13 @@ static void conf_print(const struct ctx *c)
info(" our link-local: %s",
inet_ntop(AF_INET6, &c->ip6.our_tap_ll,
buf, sizeof(buf)));
+ for (i = 1; i < UINT16_MAX; i++) {
+ int offset = 0;
+
+ while (dhcpv6_opt_to_str(i, optbuf,
+ sizeof(optbuf), &offset))
+ info(" option %u: %s", i, optbuf);
+ }
dns6:
for (i = 0; i < ARRAY_SIZE(c->ip6.dns); i++) {
@@ -1317,6 +1327,7 @@ void conf(struct ctx *c, int argc, char **argv)
{"conf-path", required_argument, NULL, 'c' },
{"chroot-fallback", no_argument, NULL, 32 },
{"no-pidns", no_argument, NULL, 33 },
+ {"dhcpv6-opt", required_argument, NULL, 36 },
{ 0 },
};
const char *optstring = "+dqfel:hs:c:F:I:p:P:m:a:n:M:g:i:o:D:S:H:461t:u:T:U:";
@@ -1329,6 +1340,7 @@ void conf(struct ctx *c, int argc, char **argv)
unsigned long max_mtu = IP_MAX_MTU;
struct fqdn *dnss = c->dns_search;
unsigned int ifi4 = 0, ifi6 = 0;
+ unsigned long dhcpv6_opt_code;
bool opt_a_is_prefix = false;
const char *logfile = NULL;
char *runas = NULL;
@@ -1567,6 +1579,19 @@ void conf(struct ctx *c, int argc, char **argv)
c->no_pidns = true;
break;
+ case 36:
+ p = optarg;
+
+ if (!parse_unsigned(&p, 0, &dhcpv6_opt_code) ||
+ !parse_literal(&p, ","))
+ die("--dhcpv6-opt requires CODE,VALUE format");
+
+ if (dhcpv6_opt_code == 0 ||
+ dhcpv6_opt_code > UINT16_MAX)
+ die("Invalid DHCPv6 option code: %s", optarg);
+
+ dhcpv6_set_opt(dhcpv6_opt_code, p);
+ break;
case 'd':
c->debug = 1;
c->quiet = 0;
diff --git a/dhcpv6.c b/dhcpv6.c
index 29c7e320..a98f1a9c 100644
--- a/dhcpv6.c
+++ b/dhcpv6.c
@@ -31,6 +31,8 @@
#include "passt.h"
#include "tap.h"
#include "log.h"
+#include "inany.h"
+#include "parse.h"
/**
* struct opt_hdr - DHCPv6 option header
@@ -63,6 +65,11 @@ struct opt_hdr {
#define OPT_MAX_SIZE IPV6_MIN_MTU - (sizeof(struct ipv6hdr) + \
UDP_MSG_HDR_SIZE)
+#define for_each_in6_off(off, start, len) \
+ for ((off) = (start); \
+ (off) + sizeof(struct in6_addr) <= (unsigned int)(len); \
+ (off) += sizeof(struct in6_addr))
+
/**
* struct opt_client_id - DHCPv6 Client Identifier option
* @hdr: Option header
@@ -279,7 +286,351 @@ static struct resp_not_on_link_t {
};
/**
- * dhcpv6_opt() - Get option from DHCPv6 message
+ * enum dhcpv6_opt_type - DHCPv6 option value types
+ * @DHCPV6_OPT_NONE: Unsupported or unknown option
+ * @DHCPV6_OPT_STR: Variable-length string
+ * @DHCPV6_OPT_IPV6: Single IPv6 address
+ * @DHCPV6_OPT_IPV6_LIST: Multiple IPv6 addresses, comma-separated
+ * @DHCPV6_OPT_UINT8: Unsigned 8-bit integer
+ * @DHCPV6_OPT_UINT16: Unsigned 16-bit integer
+ * @DHCPV6_OPT_UINT32: Unsigned 32-bit integer
+ * @DHCPV6_OPT_VENDOR_CLASS: Enterprise number + length-prefixed data
+ * @DHCPV6_OPT_LEN_STR_LIST: Length-prefixed string list
+ */
+enum dhcpv6_opt_type {
+ DHCPV6_OPT_NONE,
+ DHCPV6_OPT_STR,
+ DHCPV6_OPT_IPV6,
+ DHCPV6_OPT_IPV6_LIST,
+ DHCPV6_OPT_UINT8,
+ DHCPV6_OPT_UINT16,
+ DHCPV6_OPT_UINT32,
+ DHCPV6_OPT_VENDOR_CLASS,
+ DHCPV6_OPT_LEN_STR_LIST,
+};
+
+/**
+ * dhcpv6_opt - Description of DHCPv6 options (value type), indexed by code
+ * RFC 9915 options: 7, 15, 16, 32, 82, 83
+ * RFC 5970 options: 59, 60
+ * RFC 4075 options: 31
+ */
+static const enum dhcpv6_opt_type dhcpv6_opt[] = {
+ [7] = DHCPV6_OPT_UINT8, /* Preference */
+ [15] = DHCPV6_OPT_LEN_STR_LIST, /* User Class */
+ [16] = DHCPV6_OPT_VENDOR_CLASS, /* Vendor Class */
+ [31] = DHCPV6_OPT_IPV6_LIST, /* SNTP Servers */
+ [32] = DHCPV6_OPT_UINT32, /* Information Refresh Time */
+ [59] = DHCPV6_OPT_STR, /* Boot File URL */
+ [60] = DHCPV6_OPT_LEN_STR_LIST, /* Boot File Params */
+ [82] = DHCPV6_OPT_UINT32, /* SOL_MAX_RT */
+ [83] = DHCPV6_OPT_UINT32, /* INF_MAX_RT */
+};
+
+/**
+ * dhcpv6_opt_parse() - Parse a DHCPv6 option value string into binary
+ * @code: DHCPv6 option code
+ * @str: Value string from command line
+ * @buf: Output buffer for binary value
+ * @buf_len: Size of output buffer
+ *
+ * Return: number of bytes written to @buf, or -1 on error
+ */
+static int dhcpv6_opt_parse(uint16_t code, const char *str,
+ uint8_t *buf, size_t buf_len)
+{
+ enum dhcpv6_opt_type type;
+ union inany_addr addr;
+ unsigned long val;
+ uint16_t slen_net;
+ sa_family_t af;
+ uint8_t width;
+ uint32_t ent;
+ size_t slen;
+ int len;
+
+ if (!*str)
+ return -1;
+
+ if (code >= ARRAY_SIZE(dhcpv6_opt))
+ return -1;
+
+ type = dhcpv6_opt[code];
+
+ switch (type) {
+ case DHCPV6_OPT_NONE:
+ return -1;
+ case DHCPV6_OPT_IPV6:
+ case DHCPV6_OPT_IPV6_LIST:
+ len = 0;
+
+ do {
+ if (len + sizeof(struct in6_addr) > buf_len)
+ return -1;
+
+ if (!parse_inany_(&str, &addr, &af) || af != AF_INET6)
+ return -1;
+
+ memcpy(buf + len, &addr.a6, sizeof(struct in6_addr));
+ len += sizeof(struct in6_addr);
+
+ if (type == DHCPV6_OPT_IPV6)
+ break;
+ } while (parse_literal(&str, ","));
+
+ if (!len || !parse_eoi(str))
+ return -1;
+
+ return len;
+ case DHCPV6_OPT_UINT8:
+ case DHCPV6_OPT_UINT16:
+ case DHCPV6_OPT_UINT32:
+ if (type == DHCPV6_OPT_UINT8)
+ width = 1;
+ else if (type == DHCPV6_OPT_UINT16)
+ width = 2;
+ else
+ width = 4;
+
+ if (buf_len < width)
+ return -1;
+
+ if (!parse_unsigned(&str, 0, &val) || !parse_eoi(str) ||
+ val >= (1ULL << (width * 8)))
+ return -1;
+
+ if (type == DHCPV6_OPT_UINT16) {
+ uint16_t v16 = htons(val);
+ memcpy(buf, &v16, sizeof(v16));
+ } else if (type == DHCPV6_OPT_UINT32) {
+ uint32_t v32 = htonl(val);
+ memcpy(buf, &v32, sizeof(v32));
+ } else {
+ buf[0] = val;
+ }
+
+ return width;
+ case DHCPV6_OPT_STR:
+ slen = strlen(str);
+
+ if (slen > buf_len)
+ return -1;
+
+ memcpy(buf, str, slen);
+
+ return slen;
+ case DHCPV6_OPT_VENDOR_CLASS:
+ if (!parse_unsigned(&str, 0, &val) ||
+ !parse_literal(&str, ":") || val > UINT32_MAX)
+ return -1;
+
+ slen = strlen(str);
+ if (!slen)
+ return -1;
+
+ len = sizeof(uint32_t) + sizeof(uint16_t) + slen;
+ if ((size_t)len > buf_len)
+ return -1;
+
+ ent = htonl(val);
+ memcpy(buf, &ent, sizeof(ent));
+
+ slen_net = htons(slen);
+ memcpy(buf + sizeof(uint32_t), &slen_net, sizeof(slen_net));
+
+ memcpy(buf + sizeof(uint32_t) + sizeof(uint16_t), str, slen);
+
+ return len;
+ case DHCPV6_OPT_LEN_STR_LIST:
+ len = 0;
+
+ while (*str) {
+ slen = strcspn(str, ",");
+ if (!slen)
+ return -1;
+
+ if (len + (int)(sizeof(uint16_t) + slen) > (int)buf_len)
+ return -1;
+
+ slen_net = htons(slen);
+ memcpy(buf + len, &slen_net, sizeof(slen_net));
+ len += sizeof(uint16_t);
+
+ memcpy(buf + len, str, slen);
+ len += slen;
+
+ str += slen;
+ if (*str == ',')
+ str++;
+ }
+
+ if (!len)
+ return -1;
+
+ return len;
+ }
+
+ return -1;
+}
+
+/**
+ * struct dhcpv6_user_opts - User-specified DHCPv6 options from --dhcpv6-opt
+ * @val: Binary option value in wire format
+ * @len: Length of @val in bytes, 0 if not set
+ */
+static struct {
+ uint8_t val[UINT16_MAX];
+ int len;
+} dhcpv6_user_opts[ARRAY_SIZE(dhcpv6_opt)];
+
+/**
+ * dhcpv6_opt_to_str() - Render a binary DHCPv6 option value to printable string
+ * @code: DHCPv6 option code
+ * @buf: Output string buffer
+ * @buf_len: Size of output buffer
+ * @off: Opaque byte offset into option value, caller sets to 0 initially
+ *
+ * Return: pointer to @buf if option data was rendered, NULL when done
+ */
+const char *dhcpv6_opt_to_str(uint16_t code, char *buf, size_t buf_len,
+ int *off)
+{
+ enum dhcpv6_opt_type type;
+ uint8_t *opt_val;
+ uint32_t val = 0;
+ int buf_off = 0;
+ unsigned int i;
+ uint16_t slen;
+ int *opt_len;
+
+ if (code >= ARRAY_SIZE(dhcpv6_user_opts))
+ return NULL;
+
+ opt_len = &dhcpv6_user_opts[code].len;
+ if (!*opt_len)
+ return NULL;
+
+ opt_val = dhcpv6_user_opts[code].val;
+ type = dhcpv6_opt[code];
+
+ switch (type) {
+ case DHCPV6_OPT_IPV6:
+ case DHCPV6_OPT_IPV6_LIST:
+ for_each_in6_off(i, *off, *opt_len) {
+ if (buf_off) {
+ if (buf_off + 1 >= (int)buf_len)
+ break;
+ buf[buf_off++] = ',';
+ }
+ if (!inet_ntop(AF_INET6, opt_val + i,
+ buf + buf_off, buf_len - buf_off))
+ break;
+ buf_off += strlen(buf + buf_off);
+ *off = i + sizeof(struct in6_addr);
+ }
+
+ if (!buf_off)
+ return NULL;
+
+ return buf;
+ case DHCPV6_OPT_UINT8:
+ case DHCPV6_OPT_UINT16:
+ case DHCPV6_OPT_UINT32:
+ if (*off)
+ return NULL;
+
+ if (*opt_len == 1) {
+ val = opt_val[0];
+ } else if (*opt_len == 2) {
+ uint16_t v16;
+ memcpy(&v16, opt_val, sizeof(v16));
+ val = ntohs(v16);
+ } else if (*opt_len == 4) {
+ memcpy(&val, opt_val, sizeof(val));
+ val = ntohl(val);
+ }
+
+ (void)snprintf(buf, buf_len, "%u", val);
+ *off = *opt_len;
+ return buf;
+ case DHCPV6_OPT_STR:
+ if (*off)
+ return NULL;
+
+ (void)snprintf(buf, buf_len, "%.*s", *opt_len, opt_val);
+ *off = *opt_len;
+ return buf;
+ case DHCPV6_OPT_VENDOR_CLASS:
+ if (*off)
+ return NULL;
+
+ if (*opt_len < (int)(sizeof(uint32_t) + sizeof(uint16_t)))
+ return NULL;
+
+ memcpy(&val, opt_val, sizeof(val));
+ memcpy(&slen, opt_val + sizeof(uint32_t), sizeof(slen));
+
+ (void)snprintf(buf, buf_len, "%u:%.*s",
+ ntohl(val), ntohs(slen),
+ opt_val + sizeof(uint32_t) + sizeof(uint16_t));
+ *off = *opt_len;
+ return buf;
+ case DHCPV6_OPT_LEN_STR_LIST:
+ if (*off)
+ return NULL;
+
+ i = 0;
+ while (i + sizeof(uint16_t) <= (unsigned int)*opt_len) {
+ memcpy(&slen, opt_val + i, sizeof(slen));
+ slen = ntohs(slen);
+ i += sizeof(uint16_t);
+
+ if (i + slen > (unsigned int)*opt_len)
+ break;
+
+ if (buf_off) {
+ if (buf_off + 1 >= (int)buf_len)
+ return NULL;
+ buf[buf_off++] = ',';
+ }
+ if (buf_off + slen >= (int)buf_len)
+ return NULL;
+ memcpy(buf + buf_off, opt_val + i, slen);
+ buf_off += slen;
+ i += slen;
+ }
+ buf[buf_off] = '\0';
+ *off = *opt_len;
+ return buf;
+ default:
+ return NULL;
+ }
+}
+
+/**
+ * dhcpv6_set_opt() - Parse and store a user-specified DHCPv6 option
+ * @code: DHCPv6 option code
+ * @val_str: Value string from command line
+ */
+void dhcpv6_set_opt(uint16_t code, const char *val_str)
+{
+ int ret;
+
+ if (code >= ARRAY_SIZE(dhcpv6_opt) ||
+ dhcpv6_opt[code] == DHCPV6_OPT_NONE)
+ die("DHCPv6 option %u is not supported", code);
+
+ ret = dhcpv6_opt_parse(code, val_str,
+ dhcpv6_user_opts[code].val,
+ sizeof(dhcpv6_user_opts[code].val));
+ if (ret < 0)
+ die("Invalid value for DHCPv6 option %u: %s", code, val_str);
+
+ dhcpv6_user_opts[code].len = ret;
+}
+
+/**
+ * dhcpv6_get_opt() - Get option from DHCPv6 message
* @data: Buffer with options, set to matching option on return
* @type: Option type to look up, network order
*
@@ -287,7 +638,7 @@ static struct resp_not_on_link_t {
* or false on malformed or missing option and @data is
* unmodified.
*/
-static bool dhcpv6_opt(struct iov_tail *data, uint16_t type)
+static bool dhcpv6_get_opt(struct iov_tail *data, uint16_t type)
{
struct iov_tail head = *data;
struct opt_hdr o_storage;
@@ -334,13 +685,13 @@ static bool dhcpv6_ia_notonlink(struct iov_tail *data,
foreach(ia_type, ia_types) {
current = *data;
- while (dhcpv6_opt(¤t, *ia_type)) {
+ while (dhcpv6_get_opt(¤t, *ia_type)) {
ia_base = current;
ia = IOV_REMOVE_HEADER(¤t, ia_storage);
if (!ia || ntohs(ia->hdr.l) < OPT_VSIZE(ia_na))
goto notfound;
- while (dhcpv6_opt(¤t, OPT_IAAADR)) {
+ while (dhcpv6_get_opt(¤t, OPT_IAAADR)) {
h = IOV_PEEK_HEADER(¤t, h_storage);
if (!h || ntohs(h->l) != OPT_VSIZE(ia_addr))
goto notfound;
@@ -523,7 +874,7 @@ static size_t dhcpv6_client_fqdn_fill(const struct iov_tail *data,
o = (struct opt_client_fqdn *)(buf + offset);
o->flags = 0x00;
encode_domain_name(o->domain_name, c->fqdn);
- if (dhcpv6_opt(¤t, OPT_CLIENT_FQDN)) {
+ if (dhcpv6_get_opt(¤t, OPT_CLIENT_FQDN)) {
struct opt_client_fqdn req_opt_storage;
struct opt_client_fqdn const *req_opt;
@@ -598,19 +949,19 @@ int dhcpv6(struct ctx *c, struct iov_tail *data,
return -1;
client_id_base = *data;
- if (dhcpv6_opt(&client_id_base, OPT_CLIENTID))
+ if (dhcpv6_get_opt(&client_id_base, OPT_CLIENTID))
client_id = IOV_PEEK_HEADER(&client_id_base, client_id_storage);
if (!client_id || ntohs(client_id->l) > OPT_VSIZE(client_id))
return -1;
opt = *data;
- if (dhcpv6_opt(&opt, OPT_SERVERID))
+ if (dhcpv6_get_opt(&opt, OPT_SERVERID))
server_id = IOV_PEEK_HEADER(&opt, server_id_storage);
if (server_id && ntohs(server_id->hdr.l) != OPT_VSIZE(server_id))
return -1;
opt = *data;
- if (dhcpv6_opt(&opt, OPT_IA_NA))
+ if (dhcpv6_get_opt(&opt, OPT_IA_NA))
ia = IOV_PEEK_HEADER(&opt, ia_storage);
if (ia && ntohs(ia->hdr.l) < MIN(OPT_VSIZE(ia_na), OPT_VSIZE(ia_ta)))
return -1;
@@ -644,7 +995,7 @@ int dhcpv6(struct ctx *c, struct iov_tail *data,
memcmp(&resp.server_id, server_id, sizeof(resp.server_id)))
return -1;
- if (ia || dhcpv6_opt(data, OPT_IA_TA))
+ if (ia || dhcpv6_get_opt(data, OPT_IA_TA))
return -1;
info("DHCPv6: received INFORMATION_REQUEST, sending REPLY");
diff --git a/dhcpv6.h b/dhcpv6.h
index 1015a1a7..6cefd15b 100644
--- a/dhcpv6.h
+++ b/dhcpv6.h
@@ -9,5 +9,8 @@
int dhcpv6(struct ctx *c, struct iov_tail *data,
const struct in6_addr *saddr, const struct in6_addr *daddr);
void dhcpv6_init(const struct ctx *c);
+void dhcpv6_set_opt(uint16_t code, const char *val_str);
+const char *dhcpv6_opt_to_str(uint16_t code, char *buf, size_t buf_len,
+ int *off);
#endif /* DHCPV6_H */
diff --git a/passt.1 b/passt.1
index 0b780fec..54328b1b 100644
--- a/passt.1
+++ b/passt.1
@@ -440,6 +440,37 @@ Send \fIname\fR as DHCP option 12 (hostname).
FQDN to configure the client with.
Send \fIname\fR as Client FQDN: DHCP option 81 and DHCPv6 option 39.
+.TP
+.BR \-\-dhcpv6-opt " " \fICODE\fR,\fIVALUE\fR
+Set DHCPv6 option \fICODE\fR to \fIVALUE\fR. The value format depends
+on the option type and is determined automatically from the option code.
+Multiple IPv6 addresses are comma-separated.
+This option can be specified multiple times. If the same option code is
+given more than once, the last value wins.
+.RS
+.TP
+.B String options
+59 (Boot File URL, RFC 5970)
+.TP
+.B Length-prefixed string list options (comma-separated entries)
+15 (User Class, RFC 9915), 60 (Boot File Params, RFC 5970).
+Each comma-separated entry is encoded with a 2-byte length prefix.
+Example: \fB\-\-dhcpv6-opt 15,class1,class2\fR.
+.TP
+.B Vendor class options (ENTERPRISE:DATA format)
+16 (Vendor Class, RFC 9915).
+VALUE is \fIENTERPRISE\fR:\fIDATA\fR where \fIENTERPRISE\fR is the IANA
+Private Enterprise Number and \fIDATA\fR is the vendor class string.
+Example: \fB\-\-dhcpv6-opt 16,0:HTTPClient\fR for UEFI HTTP Boot.
+.TP
+.B IPv6 address list options (comma-separated)
+31 (SNTP Servers)
+.TP
+.B Integer options
+7 (Preference, 8-bit), 32 (Information Refresh Time, 32-bit),
+82 (SOL_MAX_RT, 32-bit), 83 (INF_MAX_RT, 32-bit)
+.RE
+
.TP
.BR \-t ", " \-\-tcp-ports " " \fIspec
Configure TCP port forwarding to guest or namespace. \fIspec\fR can be either:
--
2.55.0
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