Stateful DHCPv6 Prefix delegation (Rapid-commit) [4/4]


Picture1: DHCPv6 prefix delegation topology


R1 configuration [> 12.4(24) T]:

Prefix delegation gives the possibility to centrally control IPv6 addresses used in remote sites.

Router R1 acts as the primary DHCPv6 server for the client router R2, which in turn acts as DHCP server for final clients.

For example R1 can be a service provider MPLS PE (Provider Edge) router, R2 a client CPE (Customer Premise Equipment) router and final DHCP clients (router R3 in our case).

R1 controls which prefix pools to delegate to a remote router after matching the configured client DUID (in our case 00030001CA02188C0008) present in the SOLLICIT message received from the client.

R1:

ipv6 dhcp pool PDCONF


prefix-delegation 2001:DB8:23::/48 00030001CA02188C0008


dns-server 2001:DB8::57


domain-name nouri.com

The DHCPv6 server functionality is enabled on the interface fa0/0 facing R2, the intermediate server that will receive the delegated prefix 2001:DB8:23::/48.

interface FastEthernet0/0

ipv6 address 2001:DB8:12::1/64


ipv6 nd other-config-flag


ipv6 dhcp server PDCONF rapid-commit

R2 configuration [> 12.4(24) T]:

Router R2 interfacefa0/0, facing the DHCPv6 server R1, acts as DHCPv6 client

interface FastEthernet0/0

ipv6 address 2001:DB8:12::2/64

ipv6 enable


ipv6 dhcp client pd PDCONF rapid-commit

Router R2 interface fa0/1, facing the client R3, acts as a gateway router by announcing addresses from the delegated pool after assigning an interface ID to itself first, in this case (::2).

interface FastEthernet0/1


ipv6 address PDCONF ::2/64

ipv6 enable

And the client receives a prefix through SLAAC Router Advertisement.

R3:

interface FastEthernet0/0


ipv6 address autoconfig

ipv6 enable

R3(config-if)#do sh ipv6 interface brief

FastEthernet0/0 [up/up]

FE80::C800:1AFF:FECC:8


2001:DB8:23:0:C800:1AFF:FECC:8


R3(config-if)#

Verification:

R1 (Server):

R1#sh ipv6 dhcp pool

DHCPv6 pool: PDCONF

Static bindings:

Binding for client 00030001CA021FF80008

IA PD: IA ID not specified; being used by 00040001


Prefix: 2001:DB8:23::/48

preferred lifetime 604800, valid lifetime 2592000


DNS server: 2001:DB8::57


Domain name: nouri.com


Active clients: 1

R1#

The PDCONF pool is delegated to the client with the id=00030001CA021FF80008

R1#sh ipv6 dhcp interface

FastEthernet0/0 is in server mode

Using pool: PDCONF

Preference value: 0

Hint from client: ignored

Rapid-Commit: enabled

R1#

R2 (intermediate client/server) before delegation:

R2#sh ipv6 dhcp interface

FastEthernet0/0 is in client mode

Prefix State is SOLICIT (7)

Retransmission timer expires in 00:00:42

Address State is IDLE

Prefix Rapid-Commit: enabled

Address Rapid-Commit: disabled

FastEthernet0/1 is in server mode

Using pool: PDCONF

Preference value: 0

Hint from client: ignored

Rapid-Commit: enabled

R2#

R2 (intermediate client/server) after delegation:

R2#sh ipv6 dhcp int

FastEthernet0/0 is in client mode


Prefix State is OPEN

Renew will be sent in 3d11h

Address State is IDLE

List of known servers:

Reachable via address: FE80::C803:CFF:FEBC:8


DUID: 00030001CA030CBC0008

Preference: 0

Configuration parameters:

IA PD: IA ID 0x00040001, T1 302400, T2 483840


Prefix: 2001:DB8:23::/48

preferred lifetime 604800, valid lifetime 2592000

expires at Dec 10 2011 02:58 AM (2591829 seconds)


DNS server: 2001:DB8::57


Domain name: nouri.com

Information refresh time: 0


Prefix name: PDCONF

Prefix Rapid-Commit: enabled

Address Rapid-Commit: disabled

FastEthernet0/1 is in server mode

Using pool: PDCONF

Preference value: 0

Hint from client: ignored

Rapid-Commit: enabled

R2#

Picture2: DHCP SOLLICIT sent by R2 to R1

DHCPv6 server responding to R2 SOLLICIT

R1(config-dhcpv6)#

*Nov 10 02:58:18.579: IPv6 DHCP: Received SOLICIT from FE80::C802:1FFF:FEF8:8 on FastEthernet0/0

*Nov 10 02:58:18.583: IPv6 DHCP: Using interface pool PDCONF

*Nov 10 02:58:18.583: IPv6 DHCP: Creating binding for FE80::C802:1FFF:FEF8:8 in pool PDCONF

*Nov 10 02:58:18.583: IPv6 DHCP: Allocating IA_PD 00040001 in binding for FE80::C802:1FFF:FEF8:8

*Nov 10 02:58:18.587: IPv6 DHCP: Allocating prefix 2001:DB8:23::/48 in binding for FE80::C802:1FFF:FEF8:8, IAID 00040001

*Nov 10 02:58:18.591: IPv6 DHCP: Sending REPLY to FE80::C802:1FFF:FEF8:8 on FastEthernet0/0

R1(config-dhcpv6)#

Picture3: DHCP REPLY sent by R1 (the delegating server) to R2

About DUID (DHCP Unique Identifier)

DUID uniquely identifies the pair (client, server), it is based on the client and the server link-local address and the lowest numbered interface MAC.

DUID which remains the same across reboots.

rfc3315:

"DHCP clients use DUIDs to identify a server in messages where a server needs to be identified."
"The DUID is designed to be unique across all DHCP clients and servers, and stable for any specific client or 
server - that is, the DUID used by a client or server SHOULD NOT change over time if at all possible; for example,
a device's DUID should not change as a result of a change in the device's network hardware." 
"DUID is that the DUID must be globally unique"
... 
DUID Based on Link-layer Address [DUID-LL] 
3(2 octets)+ HW type(2 octets)+ LL(6 octets)

R1: DUID on DHCPv6 server role

R1#sh ipv6 dhcp

This device’s DHCPv6 unique identifier(DUID): 00030001CA030CBC0008

R1# sh ipv6 interface brief

FastEthernet0/0 [up/up]

FE80::C803:CFF:FEBC:8

2001:DB8:12::1


R1#

R2: DUID on DHCPv6 client/server role

R2#sh ipv6 dhcp

This device’s DHCPv6 unique identifier(DUID): 00030001CA021FF80008

R2#

R2#sh ipv6 interface brief

FastEthernet0/0 [up/up]

FE80::C802:1FFF:FEF8:8

2001:DB8:12::2


R2#

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About ajnouri
Se vi deziras sekure komuniki eksterbloge, jen mia publika (GPG) ŝlosilo: My public key for secure communication: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x41CCDE1511DF0EB8

4 Responses to Stateful DHCPv6 Prefix delegation (Rapid-commit) [4/4]

  1. Pingback: IOS DHCPv6 deployment schemes « CCIE, the beginning!

  2. Alessandro says:

    Hey your post are unbelievable!!!!! Please don’ t stop to create them. I think you could do an e-book with all your best sample.

    Ale

  3. Matt Wilson says:

    Great post, thanks. Does the command: prefix-delegation 2001:DB8:23::/48 00030001CA02188C0008 refer to R1 or the client router?

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