DHCPv4 Operation PDF

DHCP DHCPv4 Operation Introducing DHCPv4 ▪ DHCPv4 assigns IPv4 addresses and other network configuration information dynamically. A dedicated DHCPv4 server is scalable and relatively easy to manage. A Cisco router can be configured to provide DHCPv4 services in a small network....

DHCP DHCPv4 Operation Introducing DHCPv4 ▪ DHCPv4 assigns IPv4 addresses and other network configuration information dynamically. A dedicated DHCPv4 server is scalable and relatively easy to manage. A Cisco router can be configured to provide DHCPv4 services in a small network. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 2 DHCPv4 Operation DHCPv4 Operation ▪ Four step process for a client to obtain a lease: 1. DHCP Discover (DHCPDISCOVER) - client uses Layer 2 and Layer 3 broadcast addresses to find a DHCP server. 2. DHCP Offer (DHCPOFFER) - DHCPv4 server sends the binding DHCPOFFER message to the requesting client as a unicast. 3. DHCP Request (DHCPREQUEST) – the client sends back a broadcast DHCPREQUEST in response to the servers offer. 4. DHCP Acknowledgment (DHCPACK) – the server replies with a unicast DHCPACK message. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 3 DHCPv4 Operation DHCPv4 Message Format ▪ DHCPv4 messages: If sent from the client, use UDP source port 68 and destination port 67. If sent from the server, use UDP source port 67 and destination port 68. Format and fields of a DHCPv4 Message © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 4 DHCPv4 Operation DHCPv4 Discover and Offer Messages © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 5 Configuring a Basic DHCPv4 Server Configuring a Basic DHCPv4 Server ▪ Configuring a Cisco router as a DHCPv4 server: Excluding IPv4 Addresses – ip dhcp excluded-address can exclude a single address or a range of addresses from being assigned. Configuring a DHCPv4 Pool - ip dhcp pool pool-name command creates a pool with the specified name and puts the router in DHCPv4 configuration mode. Address pool assigned using network command. Default gateway assigned using default-router command. Other commands are optional. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 6 Configuring a Basic DHCPv4 Server Verifying DHCPv4 ▪ Verify DHCPv4 configuration using the show running-config |section dhcp command. ▪ Verify the operation of DHCPv4 using the show ip dhcp binding command. ▪ Verify that messages are being received or sent by the router using the show ip dhcp server statistics command. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 7 Configuring DHCPv4 Client Configuring a Wireless Router as a DHCPv4 Client ▪ Wireless routers are set to receive IPv4 addressing information automatically from the ISP. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 8 Troubleshoot DHCPv4 Verify Router DHCPv4 Configuration ▪ Verify DHCPv4 Relay - use show running-config command to verify that the ip helper address is configured. ▪ Verify DHCPv4 configuration - use the show running-config | include no service dhcp command to verify dhcp is enabled because there is no match for the no service dhcp. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 9