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ccna cost philippines.5 If the Solicit message does not carry the Rapid Commit option, or if the Solicit message carries the Rapid Commit option but the DHCPv6 server does not support the rapid allocation process, the DHCPv6 server replies with the link-local address of its own sending interface as the source and the source address of the Solicit message sent by the client as the destination Unicast Advertise message informing the client of the IPv6 address/prefix and network configuration parameters that can be assigned to it. If the Solicit message carries the Rapid Commit option and the DHCPv6 server supports the rapid assignment process, go to step 7 and reply directly to the Reply message, a rapid assignment process called DHCPv6 two-step interactive address assignment.6 If the DHCPv6 client receives an Advertise message from multiple servers, it selects the server with the highest priority based on the server priority and other parameters in the Advertise message, and sends a Request multicast message to all servers with the link-local address of its own NIC as the source and the FF02::l:2 multicast address as the destination. The message carries the DUID (DHCP UniqueIdentifier) of the selected DHCPv6 server7 The DHCPv6 server replies to the unicast Reply message with the link-local address of its own sending interface as the source and the source address of the Advertise message sent by the client as the destination, confirming that the address/prefix and network configuration parameters are assigned to the client for use.8 The DHCPv6 client completes the stateful DHCPv6 configuration based on the parameters provided in the Reply message received. It is important to note that the DHCPv6 two-step interaction process is commonly used when there is only one DHCPv6 server in the network, while the DHCPv6 four-step interaction process is commonly used when there are multiple DHCPv6 servers in the network. If the DHCPV6 server and DHCPV6 client are located on different networks, then the IPv6 router can be configured as a DHCPv6 relay agent. Configuring a DHCPv6 relay agent is similar to the operation of configuring an IPv4 router as a DHCPv4 relayoperation. The process of forwarding DHCPv6 messages by an IPv6 router or relay agent is slightly different from that of a DHCPv4 relay. Please find out for yourself how the DHCPv6 relay agent works, as this book will not discuss it in depth.10.3 DHCP Snooping Overview10.3.1 Types of DHCP AttacksIn LANs, DHCP servers are often used to assign IP addresses to users. The DHCP service is an unauthenticated service, i.e., clients and servers cannot verify each other's legitimacy. According to the DHCPT principle, clients broadcast to find a server and only use the network configuration parameters provided by the first responding server. If there are multiple DHCP servers in the network (one or more of which are unauthorized), the client uses the network configuration parameters supplied by the first DHCP server that responds. If the non-authorized DHCP server answers first, the last network parameters obtained by the client are unauthorized or malicious, and the client may obtain incorrect IP addresses, gateways, DNS, and other information, allowing the hacker to carry out a Man-in-the-Middle attack. In addition, the attacker is likely to maliciously obtain information from an authorized DHCP serverChapter 10 DHCP .139.repeatedly request IP addresses from the authorized DHCP server. causing the authorized DHCP server to consume all the IP addresses in the address pool while legitimate hosts are unable to request IP addresses. this is a DHCP depletion attack. The above two attacks are usually used together to first deplete the IP addresses in the address pool of the authorized DHCP server and then allow the client to apply for an IP address from a non-authorized DHCP server to perform a DHCP spoofing attack.