CCNA2 LS CH10
DHCP Options
Holds DHCP options, including several parameters required for basic DHCP operation. This field is variable in length. Both client and server may use this field.
Seconds
Identifies the number of seconds elapsed since a client began attempting to acquire or renew a lease. Used by DHCPv4 servers to prioritize replies when multiple client requests are outstanding
Hardware Type
Identifies the type of hardware used in the network. For example, 1 is Ethernet, 15 is Frame Relay, and 20 is a serial line. These are the same codes used in ARP messages.
Troubleshooting Task 4: Verify Switch Port Configuration
If the DHCPv4 client is unable to obtain an IPv4 address from the DHCPv4 server on startup, attempt to obtain an IPv4 address from the DHCPv4 server by manually forcing the client to send a DHCPv4 request.
Troubleshooting Task 5: Test DHCPv4 Operation on the Same Subnet or VLAN
It is important to distinguish whether DHCPv4 is functioning correctly when the client is on the same subnet or VLAN as the DHCPv4 server. If DHCPv4 is working correctly when the client is on the same subnet or VLAN, the problem may be the DHCP relay agent. If the problem persists even with testing DHCPv4 on the same subnet or VLAN as the DHCPv4 server, the problem may actually be with the DHCPv4 server.
DHCPv4 includes three different address allocation mechanisms to provide flexibility when assigning IP addresses:
Manual Allocation, Automatic Allocation and Dynamic Allocation.
Lease Renewal - DHCP Acknowledgment (DHCPACK)
On receiving the DHCPREQUEST message, the server verifies the lease information by returning a DHCPACK
DHCP Acknowledgment (DHCPACK)
On receiving the DHCPREQUEST message, the server verifies the lease information with an ICMP ping to that address to ensure it is not being used already, creates a new ARP entry for the client lease, and replies with a unicast DHCPACK message. The DHCPACK message is a duplicate of the DHCPOFFER, except for a change in the message type field. When the client receives the DHCPACK message, it logs the configuration information and performs an ARP lookup for the assigned address. If there is no reply to the ARP, the client knows that the IPv4 address is valid and starts using it as its own.
Boot Filename
Optionally used by a client to request a particular type of boot file in a DHCPDISCOVER message. Used by a server in a DHCPOFFER to fully specify a boot file directory and filename.
#show ip dhcp conflict
R1# show ip dhcp conflict IP address Detection Method Detection time 192.168.10.32 Ping Feb 16 2013 12:28 PM 192.168.10.64 Gratuitous ARP Feb 23 2013 08:12 AM
Router Advertisement (RA) message
RA messages are sent by routers to provide addressing information to clients configured to obtain their IPv6 addresses automatically. The RA message includes the prefix and prefix length of the local segment. A client uses this information to create its own IPv6 global unicast address. A router sends an RA message periodically, or in response to an RS message. By default, Cisco routers send RA messages every 200 seconds. RA messages are always sent to the IPv6 all-nodes multicast address FF02::1.
Gateway IP Address
Routes DHCPv4 messages when DHCPv4 relay agents are involved. The gateway address facilitates communications of DHCPv4 requests and replies between the client and a server that are on different subnets or networks.
Stateless Address Autoconfiguration (SLAAC)
SLAAC is a method in which a device can obtain an IPv6 global unicast address without the services of a DHCPv6 server. At the core of SLAAC is ICMPv6. ICMPv6 is similar to ICMPv4 but includes additional functionality and is a much more robust protocol.
Operation (OP) Code
Specifies the general type of message. A value of 1 indicates a request message; a value of 2 is a reply message.
Hardware Address Length
Specifies the length of the address.
Client Hardware Address
Specifies the physical layer of the client.
Configuring a Router as a Stateful DHCPv6 Server
Step 1. Enable IPv6 Routing As shown in Figure 1, the ipv6 unicast-routing command is required to enable IPv6 routing. This command is not necessary for the router to be a stateful DHCPv6 server, but is required for sending ICMPv6 RA messages. Step 2. Configure a DHCPv6 Pool The ipv6 dhcp pool pool-name command creates a pool and enters the router in DHCPv6 configuration mode, which is identified by the Router(config-dhcpv6)# prompt. Step 3. Configure Pool Parameters With stateful DHCPv6 all addressing and other configuration parameters must be assigned by the DHCPv6 server. The address prefix command is used to indicate the pool of addresses to be allocated by the server. The lifetime option indicates the valid and preferred lease times in seconds. As with stateless DHCPv6, the client uses the source IPv6 address from the packet that contained the RA message. Other information provided by the stateful DHCPv6 server typically includes DNS server address and the domain name. Step 4. Interface Commands The ipv6 dhcp server pool-name interface command binds the DHCPv6 pool to the interface. The router responds to stateless DHCPv6 requests on this interface with the information contained in the pool. The M flag needs to be changed from 0 to 1 using the interface command ipv6 nd managed-config-flag. This informs the device not to use SLAAC but to obtain IPv6 addressing and all configuration parameters from a stateful DHCPv6 server.
Configuring a Router as a Stateless DHCPv6 Server
Step 1. Enable IPv6 Routing Use the ipv6 unicast-routing command is required to enable IPv6 routing. This command is not necessary for the router to be a stateless DHCPv6 server, but is required for sending ICMPv6 RA messages. Step 2. Configure a DHCPv6 Pool The ipv6 dhcp pool pool-name command creates a pool and enters the router in DHCPv6 configuration mode, which is identified by the Router(config-dhcpv6)# prompt. Step 3. Configure Pool Parameters During the SLAAC process, the client received the information it needed to create an IPv6 global unicast address. Step 4. Configure the DHCPv6 Interface The ipv6 dhcp server pool-name interface configuration mode command binds the DHCPv6 pool to the interface. The router responds to stateless DHCPv6 requests on this interface with the information contained in the pool. The O flag needs to be changed from 0 to 1 using the interface command ipv6 nd other-config-flag. RA messages sent on this interface indicate that additional information is available from a stateless DHCPv6 server.
Configuring a Basic DHCPv4 Server
Step 1. Excluding IPv4 Addresses Step 2. Configuring a DHCPv4 Pool Step 3. Configuring Specific Tasks
Verify Router DHCPv4 Configuration
Step 1. Verify that the ip helper-address command is configured on the correct interface. It must be present on the inbound interface of the LAN containing the DHCPv4 client workstations and must be directed to the correct DHCPv4 server. Step 2. Verify that the global configuration command no service dhcp has not been configured. This command disables all DHCP server and relay functionality on the router. The command service dhcp does not appear in the running-config, because it is the default configuration.
Verifying DHCPv4
The #show running-config | section dhcp command output displays the DHCPv4 commands configured on R1. The "| section parameter" displays only the commands associated with DHCPv4 configuration.
DHCPv4 Discover Messages
The DHCP client sends a directed IP broadcast with a DHCPDISCOVER packet. The DHCP server is on the same segment and will pick up this request. The server notes the GIADDR field is blank; therefore, the client is on the same segment. The server also notes the hardware address of the client in the request packet.
DHCPv4 Offer Messages
The DHCP server picks an IP address from the available pool for that segment, as well as the other segment and global parameters. The DHCP server puts them into the appropriate fields of the DHCP packet. The DHCP server then uses the hardware address of A (in CHADDR) to construct an appropriate frame to send back to the client.
DHCP Discover (DHCPDISCOVER)
The DHCPDISCOVER message finds DHCPv4 servers on the network. Because the client has no valid IPv4 information at bootup, it uses Layer 2 and Layer 3 broadcast addresses to communicate with the server.
DHCPv4 Message Format
The DHCPv4 message format is used for all DHCPv4 transactions. DHCPv4 messages are encapsulated within the UDP transport protocol. DHCPv4 messages sent from the client use UDP source port 68 and destination port 67. DHCPv4 messages sent from the server to the client use UDP source port 67 and destination port 68.
Disabling DHCPv4
The DHCPv4 service is enabled, by default, on versions of Cisco IOS software that support it. To disable the service, use the #no service dhcp global configuration mode command. Use the #service dhcp global configuration mode command to re-enable the DHCPv4 server process. Enabling the service has no effect if the parameters are not configured.
Step 3. Configuring Specific Tasks
The address pool and default gateway router must be configured. Use the #network statement to define the range of available addresses. Use the #default-router command to define the default gateway router. Typically, the gateway is the LAN interface of the router closest to the client devices. One gateway is required, but you can list up to eight addresses if there are multiple gateways.
Manual Allocation
The administrator assigns a pre-allocated IPv4 address to the client, and DHCPv4 communicates only the IPv4 address to the device.
Stateless DHCPv6 client
The client sends a DHCPv6 INFORMATION-REQUEST message to the DHCPv6 server requesting only configuration parameters, such as DNS server address. The client generated its own IPv6 address using the prefix from the RA message and a self-generated Interface ID.
Stateful DHCPv6 client
The client sends a DHCPv6 REQUEST message to the server to obtain an IPv6 address and all other configuration parameters from the server.
Configuring a Router as a Stateless DHCPv6 Client
The ipv6 enable command is used because the router does not yet have a global unicast address. The ipv6 address autoconfig command enables automatic configuration of IPv6 addressing using SLAAC. An RA message is then used to inform the client router to use stateless DHCPv6.
Configuring a Router as a Stateful DHCPv6 Client
The ipv6 enable interface configuration mode command to allow the router to receive a link-local address to send RS messages and participate in DHCPv6. The ipv6 address dhcp interface configuration mode command enables the router to behave as a DHCPv6 client on this interface.
Verifying the Stateless DHCPv6 Client
The output from the show ipv6 interface command shows that the router has "Stateless address autoconfig enabled" and has an IPv6 global unicast address. The IPv6 global unicast address was created using SLAAC, which includes the prefix contained in the RA message. The IID was generated using EUI-64. DHCPv6 was not used to assign the IPv6 address. output from the debug ipv6 dhcp detail command shows the DHCPv6 messages exchanged between the client and the server. In this example, the command has been entered on the client. The INFORMATION-REQUEST message is shown because it is sent from a stateless DHCPv6 client. Notice that the client, router R3, is sending the DHCPv6 messages from its link-local address to the All_DHCPv6_Relay_Agents_and_Servers address FF02::1:2.
IPv6 global unicast address.
The prefix and prefix length in the RA message, along with EUI-64 or a randomly generated IID. To modify the RA message sent on the interface of a router to indicate stateless DHCPv6, use the following command: Router(config-if)# ipv6 nd other-config-flag
Verifying the Stateless DHCPv6 Server
The show ipv6 dhcp pool command verifies the name of the DHCPv6 pool and its parameters. The number of active clients is 0, because there is no state being maintained by the server. The show running-config command can also be used to verify all the commands that were previously configured.
Stateless DHCPv6 Option (Router Advertisement and DHCPv6)
The stateless DHCPv6 option informs the client to use the information in the RA message for addressing, but additional configuration parameters are available from a DHCPv6 server.
SLAAC and DHCPv6
The two flags are the Managed Address Configuration flag (M flag) and the Other Configuration flag (O flag). Using different combinations of the M and O flags, RA messages have one of three addressing options for the IPv6 device, as shown in the figure: SLAAC (Router Advertisement only) Stateless DHCPv6 (Router Advertisement and DHCPv6) Stateful DHCPv6 (DHCPv6 only) Regardless of the option used, it is recommended by RFC 4861 that all IPv6 devices perform Duplicate Address Detection (DAD) on any unicast address, including addresses configured using SLAAC or DHCPv6.
Automatic Configuration - DHCP
This means that when the router is connected to a cable modem; for example, it is a DHCPv4 client and requests an IPv4 address from the ISP.
SLAAC Option (Router Advertisement only)
This option instructs the client to use the information in the RA message exclusively. This includes prefix, prefix-length, DNS server, MTU, and default gateway information. There is no further information available from a DHCPv6 server. The IPv6 global unicast address is created by combining the prefix from RA and an Interface ID using either EUI-64 or a randomly generated value. RA messages are configured on an individual interface of a router. To re-enable an interface for SLAAC that might have been set to another option, the M and O flags need to be reset to their initial values of 0. This is done using the following interface configuration mode commands: Router(config-if)# no ipv6 nd managed-config-flag Router(config-if)# no ipv6 nd other-config-flag
Stateful DHCPv6 (DHCPv6 only)
This option is the most similar to DHCPv4. In this case, the RA message informs the client not to use the information in the RA message. All addressing information and configuration information must be obtained from a stateful DHCPv6 server. This is known as stateful DHCPv6 because the DHCPv6 server maintains IPv6 state information. This is similar to a DHCPv4 server allocating addresses for IPv4. The M flag indicates whether or not to use stateful DHCPv6. The O flag is not involved. The following command is used to change the M flag from 0 to 1 to signify stateful DHCPv6: Router(config-if)# ipv6 nd managed-config-flag
#ip address dhcp <interface>
To configure an Ethernet interface as a DHCP client.
Step 1. Excluding IPv4 Addresses
To exclude specific addresses, use the #ip dhcp excluded-address command. A single address or a range of addresses can be excluded by specifying the low-address and high-address of the range. Excluded addresses should include the addresses assigned to routers, servers, printers, and other devices that have been manually configured.
Troubleshooting IPv6
Troubleshooting Task 1: Resolve Conflicts Similar to IPv4 addresses, an IPv6 address lease can expire on a client that still needs to connect to the network. The show ipv6 dhcp conflict command displays any address conflicts logged by the stateful DHCPv6 server. If an IPv6 address conflict is detected, the client typically removes the address and generates a new address using either SLAAC or stateful DHCPv6. Troubleshooting Task 2: Verify Allocation Method The show ipv6 interface interface command can be used to verify the method of address allocation indicated in the RA message as indicated by the settings of the M and O flags. This information is displayed in the last lines of the output. If a client is not receiving its IPv6 address information from a stateful DHCPv6 server, it could be due to incorrect M and O flags in the RA message. Troubleshooting Task 3: Test with a Static IPv6 Address When troubleshooting any DHCP issue, whether it is DHCPv4 or DHCPv6, network connectivity can be verified by configuring a static IP address on a client workstation. In the case of IPv6, if the workstation is unable to reach network resources with a statically configured IPv6 address, the root cause of the problem is not SLAAC or DHCPv6. At this point, network connectivity troubleshooting is required. Troubleshooting Task 4: Verify Switch Port Configuration If the DHCPv6 client is unable to obtain information from a DHCPv6 server, verify that the switch port is enabled and is operating correctly. Note: If there is a switch between the client and the DHCPv6 server, and the client is unable to obtain the DHCP configuration, switch port configuration issues may be the cause. These causes may include issues from trunking and channeling, STP, and RSTP. PortFast and edge port configurations resolve the most common DHCPv6 client issues that occur with an initial installation of a Cisco switch. Troubleshooting Task 5: Test DHCPv6 Operation on the Same Subnet or VLAN If the stateless or stateful DHCPv6 server is functioning correctly, but is on a different IPv6 network or VLAN than the client, the problem may be with the DHCPv6 relay agent. The client facing interface on the router must be configured with the ipv6 dhcp relay destination command.
Troubleshooting Task 2: Verify Physical Connectivity
Use the #show interfaces <interface> command to confirm that the router interface acting as the default gateway for the client is operational. If the state of the interface is anything other than up, the port does not pass traffic, including DHCP client requests.
Client IP Address
Used by a client during lease renewal when the address of the client is valid and usable, not during the process of acquiring an address. The client puts its own IPv4 address in this field if and only if it has a valid IPv4 address while in the bound state; otherwise, it sets the field to 0.
Flags
Used by a client that does not know its IPv4 address when it sends a request. Only one of the 16 bits is used, which is the broadcast flag. A value of 1 in this field tells the DHCPv4 server or relay agent receiving the request that the reply should be sent as a broadcast.
Transaction Identifier
Used by the client to match the request with replies received from DHCPv4 servers.
Server Name
Used by the server sending a DHCPOFFER or DHCPACK message. The server may optionally put its name in this field. This can be a simple text nickname or a DNS domain name, such as dhcpserver.netacad.net.
Your IP Address
Used by the server to assign an IPv4 address to the client.
Server IP Address
Used by the server to identify the address of the server that the client should use for the next step in the bootstrap process, which may or may not be the server sending this reply. The sending server always includes its own IPv4 address in a special field called the Server Identifier DHCPv4 option.
#show ip dhcp server statistics
Used to verify that messages are being received or sent by the router. This command displays count information regarding the number of DHCPv4 messages that have been sent and received.
# show ip dhcp binding
Verify the operation of DHCPv4. This command displays a list of all IPv4 address to MAC address bindings that have been provided by the DHCPv4 service.
#dns-server
View the IPv4 address of the DNS server that is available to a DHCPv4 client is configured.
Router Solicitation (RS) message
When a client is configured to obtain its addressing information automatically using SLAAC, the client sends an RS message to the router. The RS message is sent to the IPv6 all-routers multicast address FF02::2.
Two methods in which IPv6 global unicast addresses.
- Stateless Address Autoconfiguration (SLAAC), as shown in the figure - Dynamic Host Configuration Protocol for IPv6 (Stateful DHCPv6)
SLAAC Operation
1) sends an RS message to the all-routers multicast address to inform the local IPv6 router that it needs an RA. 2) A Router receives the RS message and responds with an RA message. Included in the RA message are the prefix and prefix length of the network. The RA message is sent to the IPv6 all-nodes multicast address FF02::1, with the link-local address of the router as the IPv6 source address. 3) PC1 receives the RA message containing the prefix and prefix length for the local network. PC1 will use this information to create its own IPv6 global unicast address. PC1 now has a 64-bit network prefix, but needs a 64-bit Interface ID (IID) to create a global unicast address. This process is part of ICMPv6 Neighbor Discovery and is known as Duplicate Address Detection (DAD).
DHCPv6 Communications
When stateless DHCPv6 or stateful DHCPv6 is indicated by the RA, DHCPv6 operation is invoked. DHCPv6 messages are sent over UDP. DHCPv6 messages from the server to the client use UDP destination port 546. The client sends DHCPv6 messages to the server using UDP destination port 547. The client, now a DHCPv6 client, needs to locate a DHCPv6 server. In Figure 2, the client sends a DHCPv6 SOLICIT message to the reserved IPv6 multicast all-DHCPv6-servers address FF02::1:2. This multicast address has link-local scope, which means routers do not forward the messages to other networks. One or more DHCPv6 servers respond with a DHCPv6 ADVERTISE message as shown in Figure 3. The ADVERTISE message informs the DHCPv6 client that the server is available for DHCPv6 service. The client responds with a DHCPv6 REQUEST or INFORMATION-REQUEST message to the server, depending on whether it is using stateful or stateless DHCPv6.
DHCP Offer (DHCPOFFER)
When the DHCPv4 server receives a DHCPDISCOVER message, it reserves an available IPv4 address to lease to the client. The server also creates an ARP entry consisting of the MAC address of the requesting client and the leased IPv4 address of the client. As shown in Figure 3, the DHCPv4 server sends the binding DHCPOFFER message to the requesting client. The DHCPOFFER message is sent as a unicast, using the Layer 2 MAC address of the server as the source address and the Layer 2 MAC address of the client as the destination.
Troubleshooting Task 1: Resolve IPv4 Address Conflicts
When the client reboots, it requests an IPv4 address. If the DHCPv4 server does not respond quickly, the client uses the last IPv4 address. The situation then arises where two clients are using the same IPv4 address, creating a conflict.
DHCP Request (DHCPREQUEST)
When the client receives the DHCPOFFER from the server, it sends back a DHCPREQUEST. This message is used for both lease origination and lease renewal. When used for lease origination, the DHCPREQUEST serves as a binding acceptance notice to the selected server for the parameters it has offered and an implicit decline to any other servers that may have provided the client a binding offer. Many enterprise networks use multiple DHCPv4 servers. The DHCPREQUEST message is sent in the form of a broadcast to inform this DHCPv4 server and any other DHCPv4 servers about the accepted offer.
Lease Renewal - DHCP Request (DHCPREQUEST)
When the lease has expired, the client sends a DHCPREQUEST message directly to the DHCPv4 server that originally offered the IPv4 address. If a DHCPACK is not received within a specified amount of time, the client broadcasts another DHCPREQUEST so that one of the other DHCPv4 servers can extend the lease.
Debugging DHCPv6
When the router is configured as a stateless or stateful DHCPv6 server, the debug ipv6 dhcp detail command is useful to verify the receipt and transmission of DHCPv6 messages. As shown in the figure, a stateful DHCPv6 router has received a SOLICIT message from a client. The router is using the addressing information in its IPV6-STATEFUL pool for binding information.
Troubleshooting Task 3: Test Connectivity using a Static IP Address
When troubleshooting any DHCPv4 issue, verify network connectivity by configuring static IPv4 address information on a client workstation. If the workstation is unable to reach network resources with a statically configured IPv4 address, the root cause of the problem is not DHCPv4. At this point, network connectivity troubleshooting is required.
Lease Origination
A client starts the process with a broadcast DHCPDISCOVER message with its own MAC address to discover available DHCPv4 server
Stateful DHCPv6
A router configured for stateful DHCPv6 services have the address prefix command to provide addressing information. For stateful DHCPv6 services the ipv6 nd managed-config-flag interface configuration mode command is used. In this instance, the client ignores the addressing information in the RA message and communicates with a DHCPv6 server for both addressing and other information.
Lease Time
Administrators configure DHCPv4 servers to set the leases to time out at different intervals. The lease is typically anywhere from 24 hours to a week or more. When the lease expires, the client must ask for another address, although the client is typically reassigned the same address.
Debugging DHCPv4
As a troubleshooting task, verify that the router is receiving the DHCPv4 request from the client. This troubleshooting step involves configuring an ACL for debugging output. UDP destination ports of 67 or 68 are the typical ports used by DHCPv4 clients and servers when sending DHCPv4 messages. The extended ACL is used with the debug ip packet command to display only DHCPv4 messages. The complete debug output shows all the packets in the DHCPv4 communications between the DHCPv4 server and client. Another useful command for troubleshooting DHCPv4 operation is the debug ip dhcp server events command. This command reports server events, like address assignments and database updates. It is also used for decoding DHCPv4 receptions and transmissions.
#ipconfig /renew
Command to broadcast a DHCPDISCOVER message
Step 2. Configuring a DHCPv4 Pool
Configuring a DHCPv4 server involves defining a pool of addresses to assign. The #ip dhcp pool pool-name command creates a pool with the specified name and puts the router in DHCPv4 configuration mode, which is identified by this prompt Router(dhcp-config)#.
Hops
Controls the forwarding of messages. Set to 0 by a client before transmitting a request.
Automatic Allocation
DHCPv4 automatically assigns a static IPv4 address permanently to a device, selecting it from a pool of available addresses. There is no lease and the address is permanently assigned to the device.
#ip helper-address
DHCPv4 can be configured to relay and forward the following UDP services: Port 37: Time Port 49: TACACS Port 53: DNS Port 67: DHCP/BOOTP client Port 68: DHCP/BOOTP server Port 69: TFTP Port 137: NetBIOS name service Port 138: NetBIOS datagram service
Dynamic Allocation
DHCPv4 dynamically assigns, or leases, an IPv4 address from a pool of addresses for a limited period of time chosen by the server, or until the client no longer needs the address.
DHCPv4 Operation
DHCPv4 works in a client/server mode. When a client communicates with a DHCPv4 server, the server assigns or leases an IPv4 address to that client. The client connects to the network with that leased IP address until the lease expires. The client must contact the DHCP server periodically to extend the lease. This lease mechanism ensures that clients that move or power off do not keep addresses that they no longer need. When a lease expires, the DHCP server returns the address to the pool where it can be reallocated as necessary.
There are two ways PC1 can create its own unique IID:
EUI-64 - Using the EUI-64 process, PC1 will create an IID using its 48-bit MAC address. Randomly generated - The 64-bit IID can be a random number generated by the client operating system.
Stateless DHCPv6
For stateless DHCPv6 services the ipv6 nd other-config-flag interface configuration mode command is used. This informs the device to use SLAAC for addressing information and a stateless DHCPv6 server for other configuration parameters. The show ipv6 interface command can be used to view the current configuration for allocation method. As shown in Figure 2, the last line of the output indicates how clients obtain addresses and other parameters.
#show ip interface
command can also be used to verify the DHCPv4 relay on an interface.
# show ip interface <int>
command confirms that the interface is up and that the address was allocated by a DHCPv4 server.
# netbios-name-server
command is used to define the NetBIOS WINS server.
#ipconfig /release
command to release IPv4 allocation setting it to 0.0.0.0
#domain-name <domain>
command used to define the domain name
#show running-config | include no service dhcp
command verifies that the DHCPv4 service is enabled . If the service had been disabled, the no service dhcp command would be displayed in the output.
# show ipv6 dhcp interface
command verifies the G0/0 interface is in relay mode with IPv6 configured as the DHCPv6 server.
#show ipv6 dhcp pool
command verifies the name of the DHCPv6 pool and its parameters.
#ipconfig /all
displays the TCP/IP parameters on the PC.
#show ipv6 dhcp binding
displays the automatic binding between the link-local address of the client and the address assigned by the server.
#ipv6 dhcp relay destination
his command is configured on the interface facing the DHCPv6 client using the address of the DHCPv6 server as the destination.
Dynamic Host Configuration Protocol (DHCP)
simplifies IP address assignment to both desktop and mobile devices. Using a centralized DHCP server enables organizations to administer all dynamic IP address assignments from a single server. This practice makes IP address management more effective and ensures consistency across the organization, including branch offices. DHCP is available for both IPv4 (DHCPv4) and for IPv6 (DHCPv6).
#show ipv6 interface
verifies the IPv6 global unicast address on DHCPv6 client R3 that was assigned by the DHCPv6 server.
