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DNS and IPv6

gjb911169
Level 1
Level 1

Good afternoon,

I have a Windows 2003 server running Active Directory and maintains my DNS records. This is sitting on the 2001:db8:0:1::/64 segment. I have devices that are on my 2 and 3 segments respectively. I have entered the devices into my DNS using AAAA records. If a machine is sitting on either the 2 or 3 segments, they cannot ping by name. I have Cisco 1812 series routers running RIPng. I have enabled the following commands in my router config:

ip domain-name

ip name-address

If need be I can post the configuration files. This is a test network.

Any assistance would be appreciated.

Thanks,

Greg

24 Replies 24

Giuseppe Larosa
Hall of Fame
Hall of Fame

Hello Greg,

in ipv4 we need an ip helper-address to rely the DNS request to the DNS server

I may be wrong but if you use stateless config you should need something similar:

or hosts know what ipv6 address has the DNS server

something like the following

ipv6 dhcp pool dhcp-pool

dns-server 2001:0DB8:A:B::1

dns-server 2001:0DB8:3000:3000::42

domain-name example.com

!

interface Ethernet0/0

description Access link down to customers

ipv6 address 2001:0DB8:1234:42::1/64

ipv6 nd other-config-flag

ipv6 dhcp server dhcp-pool

see

http://www.cisco.com/en/US/docs/ios/ipv6/configuration/guide/ip6-dhcp.html#wp1055654

I don't know if this is supported in your release and device.

Hope to help

Giuseppe

I have a helper address set for v4 so there is no equal in v6 and then must be through DHCPv6? I am about to try the directions you had listed. Also here is a copy of the current configuration.

Thanks

Greg

Hello Greg,

IPv6 has abolished broadcasts it uses a lot of specialized multicast ip addresses and has the concept of Anycast.

For this basic reason an ipv6 helper address is probably not available.

So one way to do this is using DHCPv6 to pass the information of what ipv6 address has the DNS to the hosts.

Hope to help

Giuseppe

Greg,

Giuseppe is right. IPv6 Autoconfiguration will not provide a DNS server address to the clients. You can configure IPv6 Stateless DHCP on the router to pass the DNS server address to the connected workstations.

Please refer to the following document for more information on stateless DHCP.

http://www.cisco.com/en/US/products/ps6553/products_white_paper09186a00801e199d.shtml

Regards

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

Everything looks to be working based on Giuseppe's suggestion. Also thanks for the white paper. It clears a few other items up for me.

Greg

Well I thought I had this solved. DNS is not working for v6 only segments. On my 1 and 2 segments both networks are dual stacked and DNS works properly. If I attempt to use DNS from v6 only segment, I am unable to ping by name. I have been running network captures and am not seeing anything in the Router Advertisement messages.

This is what my FA1 interface shows:

ipv6_router3# sh ipv6 interface fa1

FastEthernet1 is up, line protocol is up

IPv6 is enabled, link-local address is FE80::223:4FF:FE38:9FED

No Virtual link-local address(es):

Global unicast address(es):

2001:DB8:0:4:223:4FF:FE38:9FED, subnet is 2001:DB8:0:4::/64 [EUI]

Joined group address(es):

FF02::1

FF02::2

FF02::9

FF02::1:2

FF02::1:FF38:9FED

FF05::1:3

MTU is 1500 bytes

ICMP error messages limited to one every 100 milliseconds

ICMP redirects are enabled

ICMP unreachables are sent

ND DAD is enabled, number of DAD attempts: 1

ND reachable time is 30000 milliseconds

ND advertised reachable time is 0 milliseconds

ND advertised retransmit interval is 0 milliseconds

ND router advertisements are sent every 200 seconds

ND router advertisements live for 1800 seconds

ND advertised default router preference is Medium

Hosts use stateless autoconfig for addresses.

Hosts use DHCP to obtain other configuration.

I have a DHCP Pool built for the stateless autoconfiguration to push out the additional information. Let me know if anyone wants to view the configurations.

Greg

Hi...

If these are Windows XP clients, I believe Windows XP doesn't do DNS queries over IPv6. Not sure about Vista and above...just a thought...

These are Windows XP clients. I also have Linux clients that also cannot get the DNS information. It seems as if the router is not sending out the "O" flag information. I am not seeing the DNS Server IP in the Router Advertisement.

Greg

Do names resolve on the Linux clients if you hard-code the IPv6 DNS server address in resolv.conf ? I believe sending the DNS server info within the RA is still an RFC in discussion and not implemented yet, but I'd need to double-check...

I placed it as part of the DHCP pool. There is a pool group called segment4. The DNS server and domain name are located within the DHCP pool. I had followed the Implementing DHCPv6 piece that was suggested earlier. The pool has been turned on for FA1 which routes the 4 segment through all the routers back to the 1 segment. I will try hard coding into one of the Linux machines as another troubleshooting step.

Thanks

If it's configured as a DHCPv6 option, then it should be being sent in the DHCPv6 offer packet I would assume. Did you examine the DHCPv6 packets ? And are the DHCPv6 Linux clients accepting it - any client logging available ? I haven't had much experience with DHCPv6 yet, but I've heard that implementations aren't quite fully robust yet...

I need to go back and run some more captures. I have not seen anything for DHCPv6 come across the wire. That is why I am wondering if there is something else that may need to be done with the router to start up the DHCPv6 option.

Thanks,

Greg

Here is another question. Do you need to set the routers to run also as DHCPv6 relays to properly connect back to the DNS server? Again I am not seeing any DHCP requests coming across the wire.

Greg

DNS queries shouldn't need to be relayed. You should at least see DHCPDiscovers from the DHCP clients on the wire. Are you sure the clients are sending DHCP requests ? Have you tried DHCP debugging on the router serving as a DHCP server ? Also, I'm 99.9% positive that Windows XP doesn't support DNS queries over IPv6. You mentioned that the DNS server was running Windows 2003. Are you sure 2003 supports DNS over IPv6 ?

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