02-01-2012 12:15 AM - edited 03-01-2019 05:32 PM
It possible to assign multiple IPv6 addresses to the same client with DHCPv6 server?
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02-01-2012 05:45 AM
Hello,
DHCP use client ID / MAC to unique identify a client. Internally a DHCP server built a table of IP address <-> MAC, so 1 MAC = 1 IP address, not matter IPv4 / IPv6.
Now, I've seen stories about unsupported hacks that may overcome DHCP specification, but you don't want to do this in a productive environment. For IPv4 DNSmasq was used for this kind of tricks, but for IPv6 is not working.
Dnsmasq supports IPv6 for DNS and TFTP, but not DHCP.
HTH,
Calin
02-06-2012 10:50 AM
Hello, I think this should work:
multiple IPv6 addresses to the same client with one DHCPv6 server.
I tested it on c3750 switch. The switch itself is configured as DHCPv6 server.
Switch configurations:
ipv6 dhcp pool TEST
address prefix FD00:1000::/64
address prefix FD00:2000::/64
dns-server 2001:1000::1
interface Vlan2
no ip address
ipv6 address FE80::1 link-local
ipv6 nd managed-config-flag
ipv6 dhcp server TEST
After connect a Win7 laptop to vlan2:
On c3750 switch:
#sh ipv6 dhcp binding
Client: FE80::39CB:5A96:A02:C016 (Vlan2)
DUID: 0001000113B59669A4BADBCB2897
IA NA: IA ID 0x0EA4BADB, T1 43200, T2 69120
Address: FD00:1000::4D25:5436:B52E:E6BC
preferred lifetime 86400, valid lifetime 172800
expires at Feb 03 2012 02:13 PM (172446 seconds)
Address: FD00:2000::3023:9BDF:3382:7DC4
preferred lifetime 86400, valid lifetime 172800
expires at Feb 03 2012 02:13 PM (172446 seconds)
On Win7 laptop:
ipconfig:
IPv6 Address. . . . . . . . . . . : fd00:1000::4d25:5436:b52e:e6bc
IPv6 Address. . . . . . . . . . . : fd00:2000::3023:9bdf:3382:7dc4
Link-local IPv6 Address . . . . . : fe80::39cb:5a96:a02:c016%10
Autoconfiguration IPv4 Address. . : 169.254.192.22
Subnet Mask . . . . . . . . . . . : 255.255.0.0
Default Gateway . . . . . . . . . : fe80::1%10
Is this what you are looking for?
02-01-2012 05:45 AM
Hello,
DHCP use client ID / MAC to unique identify a client. Internally a DHCP server built a table of IP address <-> MAC, so 1 MAC = 1 IP address, not matter IPv4 / IPv6.
Now, I've seen stories about unsupported hacks that may overcome DHCP specification, but you don't want to do this in a productive environment. For IPv4 DNSmasq was used for this kind of tricks, but for IPv6 is not working.
Dnsmasq supports IPv6 for DNS and TFTP, but not DHCP.
HTH,
Calin
02-01-2012 05:53 PM
Interesting. We all know that all IPv6 hosts supports multiple IPv6 addresses on the same interface. So, if we need two or more IP addresses on the same interface how we can achieve this goal? One IP = One DHCPv6 server, 2 IP = 2 DHCPv6 servers ?
02-02-2012 12:04 AM
You can add manually multiple IP addresses to an interface, but when it comes to DHCP the story it's a little bit different.
When you add manually one or more IP / IPv6, L2 to L3 mapping is done through mechanism like ARP to know where to forward traffic and to built the ARP table.
DHCP will have it's own table that will map mac address to IP address. This is done to avoid problems like assigning multiple IP addresses to the same mac address. To have what you want, you need somehow to overcome the DHCP specifications.
Usually multiple IP / one interface it's used in case of servers. And talking about server and DHCP in the same phrase is not something very common.
Cheers,
Calin
02-02-2012 12:20 AM
Unfortunally multiple IP is used not with servers, but with v6 multihomming also.
So you think 2 IP = 2 DHCPv6 servers will not work? You tested it?
02-02-2012 01:28 AM
Never test it.
The question is the following. Let's assume that you have 2 DHCP servers, not synchronized. The IPv6 device send a DHCP request, one of the servers replies and the "transaction" is done. IPv6 device has an IP address now. Now the device should ask again for another IP. I don't know if this will work.
Under Linux machine at least in theory, if you have one physical ethernet interface splited into multiple subinterfaces (like eth0:0, eth0:1) it may work.
Maybe I have time to test this in the next days.
HTH,
Calin
02-02-2012 01:32 AM
I think that both servers will reply. Need to test it.
02-03-2012 02:58 AM
Tested with 2 DHCP servers. You right!
02-06-2012 10:50 AM
Hello, I think this should work:
multiple IPv6 addresses to the same client with one DHCPv6 server.
I tested it on c3750 switch. The switch itself is configured as DHCPv6 server.
Switch configurations:
ipv6 dhcp pool TEST
address prefix FD00:1000::/64
address prefix FD00:2000::/64
dns-server 2001:1000::1
interface Vlan2
no ip address
ipv6 address FE80::1 link-local
ipv6 nd managed-config-flag
ipv6 dhcp server TEST
After connect a Win7 laptop to vlan2:
On c3750 switch:
#sh ipv6 dhcp binding
Client: FE80::39CB:5A96:A02:C016 (Vlan2)
DUID: 0001000113B59669A4BADBCB2897
IA NA: IA ID 0x0EA4BADB, T1 43200, T2 69120
Address: FD00:1000::4D25:5436:B52E:E6BC
preferred lifetime 86400, valid lifetime 172800
expires at Feb 03 2012 02:13 PM (172446 seconds)
Address: FD00:2000::3023:9BDF:3382:7DC4
preferred lifetime 86400, valid lifetime 172800
expires at Feb 03 2012 02:13 PM (172446 seconds)
On Win7 laptop:
ipconfig:
IPv6 Address. . . . . . . . . . . : fd00:1000::4d25:5436:b52e:e6bc
IPv6 Address. . . . . . . . . . . : fd00:2000::3023:9bdf:3382:7dc4
Link-local IPv6 Address . . . . . : fe80::39cb:5a96:a02:c016%10
Autoconfiguration IPv4 Address. . : 169.254.192.22
Subnet Mask . . . . . . . . . . . : 255.255.0.0
Default Gateway . . . . . . . . . : fe80::1%10
Is this what you are looking for?
02-06-2012 05:36 PM
Great! Thank you very match!
My test was incorrect. I used 2 DHCP servers with every server assign one address to the client - so the client chooses one DHCPv6 server and recieve one ipv6 address. Your test was correct - one server two DHCPv6 pools.
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