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In a previous blog post, we examined the many variations for DHCP in your Cisco environment. This included using DHCP in a classic, stateful manner, as well as using it stateless in order to assign additional IP information to clients beyond the simple address information. We remember that the challenge involves a client obtaining their IPv6 address in a stateless manner from a router that is using Stateless Autoconfiguration. This involves sending Router Advertisements that instruct the client system what IPv6 prefix to use. The client can assign its own host portion thanks to EUI-64 addressing. The challenge becomes, how can the client automatically obtain other information that it needs, such as DNS server addresses and a DNS domain name? The answer is to use DHCP. What we would actually call Stateless DHCP.
Let us examine the stateless DHCP configuration.
configure terminal ipv6 dhcp pool DHCP_POOL dns-server 2001:2000::42 domain-name mydomain.com interface fa0/0 ipv6 dhcp server DHCP_POOL ipv6 nd other-config-flag
Notice that this configuration is very straightforward and is very similar to the IPv4 implementation. Of note is the fact that we are not providing the client with IPv6 prefix information or an address in any way. The client will obtain its address through some other means, typically this is the built-in auto-configuration capability. Notice the rather confusing command “ipv6 nd other-config-flag“. This command tells the DHCP host to look to the DHCP server for the other information provided here. By other information we mean things like DNS server address and domain name information.
In another post, we will examine Address Autoconfiguration and ensure our clients can obtain their IPv6 address information, as well as this Stateless DHCP information automatically.
Anthony Sequeira CCIE, CCSI
Twitter: @compsolv
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Tags: CCIE R&S, CCIE R&S Training, ccie routing & switching training, dhcp, IPv6
hello Anthony !
thanks for that refresh and indeed it can also be part of the exam but what about the default gateway per pool with the DHCPv6 in IOS 12.4T ?
Cheers ,
michal
Hi Michal!
Thanks for the feedback and the excellent question.
As far as I know the DHCPv6 implementation (stateful or stateless) does not assign default gateways. This is part of the Neighbor Discovery process in IPv6. There is also a Default Router Preferences option for better control over this selection than NDP provides. Check out more information here:
http://www.cisco.com/en/US/docs/ios/ipv6/configuration/guide/ip6-addrg_bsc_con.html#wp1283390
hi Anthony , thanks again for pointing out the DRP option in IPCMPv6 “ipv6 nd router-preference {high | medium | low}” , with the medium as default , as we read from the doc.
So in case of such specific requirement we would enable it under different ipv6 gateways that could potentialy be configured also with stateless dhcpv6 as you propose in your example ? The other interesting scenario would be if we had GLBPv6 enabled under the gateway , not sure if the router-preference is compatible with the FHRP… Thanks for sharing.
michal
I think we are stretching it a bit for the scope of the lab, but then again, as they refresh tasks, it makes more and more sense to hammer away at practical IPv6 topics.
When this does hit the lab, just read the requirements very carefully. I love your point about FHRPs. It would take a careful read to see if they mean GLBP versus DRP.