[PATCH v2 04/11] net/tap: extend fixed MAC range to 16 bits

Stephen Hemminger
2026-02-16T23:05:12Z

The generated fixed MAC address stored the interface index in a single
byte, which wraps after 256 devices and produces duplicate MACs under
repeated hot-plug. Spread the index across the last two bytes of the
address, extending the unique range to 65536.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
drivers/net/tap/rte_eth_tap.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/net/tap/rte_eth_tap.c b/drivers/net/tap/rte_eth_tap.c
index e06e1ca079..8b6d5db37e 100644
--- a/drivers/net/tap/rte_eth_tap.c
+++ b/drivers/net/tap/rte_eth_tap.c
@@ -2274,13 +2274,15 @@ set_mac_type(const char *key __rte_unused,
return 0;

if (!strncasecmp(ETH_TAP_MAC_FIXED, value, strlen(ETH_TAP_MAC_FIXED))) {
- static int iface_idx;
-
- /* fixed mac = 02:64:74:61:70:<iface_idx> */
- memcpy((char *)user_mac->addr_bytes, "\002dtap",
- RTE_ETHER_ADDR_LEN);
- user_mac->addr_bytes[RTE_ETHER_ADDR_LEN - 1] =
- iface_idx++ + '0';
+ static uint16_t iface_idx;
+
+ /* fixed mac that is locally assigned based off of iface_idx. */
+ user_mac->addr_bytes[0] = RTE_ETHER_LOCAL_ADMIN_ADDR; /* 0x2 */
+ user_mac->addr_bytes[1] = 'd';
+ user_mac->addr_bytes[2] = 't';
+ user_mac->addr_bytes[3] = 'a';
+ user_mac->addr_bytes[4] = 'p' + (iface_idx >> 8);
+ user_mac->addr_bytes[5] = '0' + (uint8_t)iface_idx++;
goto success;
}

--
2.51.0