MAC address to IPv6 link-local address online converter

The converter

It can also be addressed directly via:
for all your API needs.

The math

Link-local IPv6 addresses are used as part of the IPv6 network auto-configuration process. Instead of getting an address via DHCP, a NIC will hop on the network with a link-local IPv6 address and with this will have to ability to do further configuration automatically (soliciting neighbors, router, et cetera).

This link-local IPv6 is infered from the NIC’s mac address.

A mac address is 48 bits, an IPv6 address is 128 bits. Here’s the conversion process step by step:

  1. take the mac address: for example 52:74:f2:b1:a8:7f
  2. throw ff:fe in the middle: 52:74:f2:ff:fe:b1:a8:7f
  3. reformat to IPv6 notation 5274:f2ff:feb1:a87f
  4. convert the first octet from hexadecimal to binary: 52 -> 01010010
  5. invert the bit at index 6 (counting from 0): 01010010 -> 01010000
  6. convert octet back to hexadecimal: 01010000 -> 50
  7. replace first octet with newly calculated one: 5074:f2ff:feb1:a87f
  8. prepend the link-local prefix: fe80::5074:f2ff:feb1:a87f
  9. done!

Going the other way

A converter to do the same operation in reverse is available here.


There have been a few interesting comments on this post, I encourage you to read them if you want to learn more about this mechanism. Specifically:

Spamassassin stats

54.46% of all emails received on akrin so far got flagged as spam by the excellent Spamassassin. This is actually not too bad compared to high profile mail service providers.

1 email that takes the cake is with a spam score of 42.2 (anything above 4 is not relayed):

Return-Path: <>
Received: from ( [])
From: "Chase bank" <>
To: <>
Subject: urgent security notification for client!
X-Spam-Level: ******************************************
X-Spam-Status: Yes, score=42.2 required=5.0

Content analysis details:

pts rule name              description
---- ---------------------- --------------------------------------------------
2.0 RCVD_IN_BL_SPAMCOP_NET RBL: Received via a relay in [Blocked - see <>]
3.0 RCVD_IN_XBL            RBL: Received via a relay in Spamhaus XBL [ listed in]
0.9 RCVD_IN_PBL            RBL: Received via a relay in Spamhaus PBL
0.6 RCVD_IN_SORBS_WEB      RBL: SORBS: sender is a abuseable web server [ listed in]
1.8 URIBL_PH_SURBL         Contains an URL listed in the PH SURBL blocklist [URIs:]
1.9 URIBL_AB_SURBL         Contains an URL listed in the AB SURBL blocklist [URIs:]
1.5 URIBL_WS_SURBL         Contains an URL listed in the WS SURBL blocklist [URIs:]
1.5 URIBL_JP_SURBL         Contains an URL listed in the JP SURBL blocklist [URIs:]
2.0 URIBL_BLACK            Contains an URL listed in the URIBL blacklist [URIs:]
3.5 BAYES_99               BODY: Bayesian spam probability is 99 to 100% [score: 1.0000]
4.3 HELO_DYNAMIC_HCC       Relay HELO'd using suspicious hostname (HCC)
4.4 HELO_DYNAMIC_IPADDR2   Relay HELO'd using suspicious hostname (IP addr 2)
0.0 FH_HELO_EQ_D_D_D_D     Helo is d-d-d-d
1.4 FROM_LOCAL_HEX         From: localpart has long hexadecimal sequence
1.9 TVD_RCVD_IP            TVD_RCVD_IP
0.7 SPF_NEUTRAL            SPF: sender does not match SPF record (neutral)
2.3 SPOOF_COM2COM          URI: URI contains ".com" in middle and end
1.6 HTML_IMAGE_ONLY_24     BODY: HTML: images with 2000-2400 bytes of words
0.0 HTML_MESSAGE           BODY: HTML included in message
1.4 MIME_QP_LONG_LINE      RAW: Quoted-printable line longer than 76 chars
0.1 RDNS_DYNAMIC           Delivered to trusted network by host with dynamic-looking rDNS
2.8 DOS_OE_TO_MX           Delivered direct to MX with OE headers