{"id":3327,"date":"2015-05-18T21:37:07","date_gmt":"2015-05-18T21:37:07","guid":{"rendered":"https:\/\/live-infoblox-blog.pantheonsite.io\/?p=3327"},"modified":"2020-05-06T10:30:12","modified_gmt":"2020-05-06T17:30:12","slug":"dhcpv6-and-the-trouble-with-mac-addresses-part-2-of-2","status":"publish","type":"post","link":"https:\/\/www.infoblox.com\/blog\/ipv6-coe\/dhcpv6-and-the-trouble-with-mac-addresses-part-2-of-2\/","title":{"rendered":"DHCPv6 and the Trouble with MAC Addresses (Part 2 of 2)"},"content":{"rendered":"

In my last post we looked briefly at a key difference between DHCPv6 and DHCPv4: the use of elements other than just the MAC address to\u00a0identify to which host and interface a particular DHCP lease belongs. Among these\u00a0DHCPv6\u00a0identification\u00a0elements the DHCP Unique Identifier (or DUID) in is the closest thing to how\u00a0a MAC address is used in DHCPv4.<\/p>\n

As quoted from\u00a0RFC 3315, Dynamic Host Configuration Protocol for IPv6 (DHCPv6)<\/a>: “DHCP servers use DUIDs to identify clients for the selection of configuration parameters and in the association of IAs with clients. DHCP clients use DUIDs to identify a server in messages where a server needs to be identified.”<\/p>\n

The more granular\u00a0host and interface identification\u00a0mechanism\u00a0facilitated by the DUID (and associated elements)\u00a0is arguably better suited to\u00a0a\u00a0IPv6-enabled\u00a0LAN\u00a0environment where interfaces have multiple addresses of different scopes. But enterprise LAN administration practice has long relied on the use of the MAC address to\u00a0reserve address leases\u00a0for particular hosts\u00a0in DHCPv4\u00a0(along with practices not directly related to DHCP such as using the MAC to control access to the network and help track host\u00a0hardware).<\/p>\n

RFC 6939,\u00a0Client Link-Layer Address Option in DHCPv6<\/i><\/a>, offers “an optional mechanism and the related\u00a0DHCPv6 option to allow first-hop DHCPv6 relay agents (relay agents\u00a0that are connected to the same link as the client) to provide the\u00a0client’s link-layer address in the DHCPv6 messages being sent towards\u00a0the server.\u201d\u00a0As we discussed in the last post, if the server is on the same link as the client, the MAC address of the originating host\u00a0can always be learned from the layer 2 frame.<\/p>\n

From the description, it sounds like RFC 6939 offers a way to preserve the\u00a0lease reservation method used in\u00a0DHCPv4. It would also allow simpler correlation of a host with both IPv4 and IPv6 addresses for management purposes.\u00a0Sounds great, right? But do DHCPv6 servers support this option yet?<\/p>\n

Well after I published the first part of this blog, a colleague pointed me to a\u00a0recent post from\u00a0Enno Rey\u00a0and Antonios Atlasis<\/a>\u00a0on\u00a0the\u00a0blog\u00a0over at Enno\u2019s excellent Infosec\/IPv6 site,\u00a0Insinuator<\/a>. As chance would have it, Antonios recently tested exactly the above\u00a0question\u00a0with both ISC DHCP\u00a04.3 and Cisco IOS XE. Seems I was picking up Enno’s and Antonios\u2019 powerful brainwaves through The Cosmic Ether\u00a0when I chose (er,\u00a0thought I was choosing) the subject to blog about.\u00a0Please do yourself a favor and\u00a0follow the link to read the whole post.<\/p>\n

I\u2019ll be back a couple of weeks with a blog discussing (the at least) 3 things that will sink your IPv6 adoption initiative.<\/p>\n","protected":false},"excerpt":{"rendered":"

In my last post we looked briefly at a key difference between DHCPv6 and DHCPv4: the use of elements other than just the MAC address to\u00a0identify to which host and interface a particular DHCP lease belongs. Among these\u00a0DHCPv6\u00a0identification\u00a0elements the DHCP Unique Identifier (or DUID) in is the closest thing to how\u00a0a MAC address is used […]<\/p>\n","protected":false},"author":319,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"_genesis_hide_title":false,"_genesis_hide_breadcrumbs":false,"_genesis_hide_singular_image":false,"_genesis_hide_footer_widgets":false,"_genesis_custom_body_class":"","_genesis_custom_post_class":"","_genesis_layout":"","footnotes":""},"categories":[17],"tags":[50,51],"class_list":{"0":"post-3327","1":"post","2":"type-post","3":"status-publish","4":"format-standard","6":"category-ipv6-coe","7":"tag-dhcp","8":"tag-ipam","9":"entry"},"acf":[],"yoast_head":"\nDHCPv6 and the Trouble with MAC Addresses (Part 2 of 2)<\/title>\n<meta name=\"description\" content=\"In my last post we looked briefly at a key difference between 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