Host Configuration: BOOTP and DHCP Chapter 2 – part 1 Host Configuration: BOOTP and DHCP Mục tiêu Sau khi hoàn thành phần này có thể: Hiểu các dạng thông tin cần thiết của hệ thống khi khởi động Hiểu cách hoạt động giao thức BOOTP Hiểu cách hoạt động DHCP Hiểu sự khác nhau giữa BOOTP and DHCP Hiểu hội thoại trạng thái truyền DHCP TCP/IP Protocol Suite

2.1 BOOTP The Bootstrap Protocol (BOOTP) là một giao thức client/server để cấu hình một máy tính không đĩa cứng hoặc một máy tính được khởi động trong lần đầu tiên. BOOTP cung cấp địa chỉ IP, net mask, địa chỉ ngầm định của router, và địa chỉ của một máy chủ. Trong phần này gồm: Nguyên tắc hoạt động Định dạng gói tin (Packet Format ) TCP/IP Protocol Suite

Figure 2.1 Client and server on the same network TCP/IP Protocol Suite

Figure 2.2 Client and server on two different networks TCP/IP Protocol Suite

Figure 2.3 Use of UDP ports TCP/IP Protocol Suite

Figure 2.4 BOOTP packet format TCP/IP Protocol Suite

Figure 2.5 Option format TCP/IP Protocol Suite

Table 2.1 Options for BOOTP TCP/IP Protocol Suite

2.2 DHCP The Dynamic Host Configuration Protocol (DHCP) cấp địa chỉ tính và động bằng thủ công hoặc tự động Trong phần này gồm: Static Address Allocation Dynamic Address Allocation Manual and Automatic Configuration Packet Format Transition States Exchanging Messages TCP/IP Protocol Suite

Note: DHCP cấp vị trí địa chỉ tĩnh và động có thể sử dụng thủ công hoặc tự động. TCP/IP Protocol Suite

Figure 2.6 DHCP packet TCP/IP Protocol Suite

Table 2.2 Options for DHCP 1: Gửi quảng bá đi tìm một DHCP server; 2: Máy chủ DHCP gửi gói tin phục vụ; 3: Gửi yêu cầu DHCP; 4: Từ chối DHCP; 5: Chấp nhận DHCP; 6: Không chấp nhận; 7: Giải phóng TCP/IP Protocol Suite

Figure 2.7 DHCP transition diagram TCP/IP Protocol Suite

Figure 2.8 Exchanging messages TCP/IP Protocol Suite

DHCP client-server scenario 223.1.1.0/24 223.1.1.1 223.1.2.1 223.1.1.2 arriving DHCP client needs address in this network 223.1.1.4 223.1.2.9 223.1.2.2 223.1.1.3 223.1.3.27 223.1.2.0/24 223.1.3.1 223.1.3.2 223.1.3.0/24

DHCP client-server scenario DHCP server: 223.1.2.5 DHCP discover src : 0.0.0.0, 68 dest.: 255.255.255.255, 67 yiaddr: 0.0.0.0 transaction ID: 654 arriving client DHCP offer src: 223.1.2.5, 67 dest: 255.255.255.255, 68 yiaddrr: 223.1.2.4 transaction ID: 654 lifetime: 3600 secs DHCP request src: 0.0.0.0, 68 dest:: 255.255.255.255, 67 yiaddrr: 223.1.2.4 transaction ID: 655 lifetime: 3600 secs DHCP ACK src: 223.1.2.5, 67 dest: 255.255.255.255, 68 yiaddrr: 223.1.2.4 transaction ID: 655 lifetime: 3600 secs

DHCP: more than IP addresses DHCP có thể gửi lại nhiều địa chỉ IP: Địa chỉ của first-hop router cho client Tên và địa chỉ IP của máy chủ DNS Mặt nạ mạng (Cho biết phần mạng, phần host)

DHCP: example DHCP UDP IP Eth Phy DHCP DHCP Máy Laptop sẽ kết nối cần địa chỉ IP của nó, địa chỉ của first-hop router, địa chỉa của DNS server: sử dụng DHCP DHCP DHCP request được đóng gói bằng UDP, đóng gói bằng IP, đóng gói theo 802.1 Ethernet DHCP DHCP UDP IP Eth Phy DHCP 168.1.1.1 Ethernet frame broadcast (dest: FFFFFFFFFFFF) on LAN, được nhận tại router đang chạy DHCP server router with DHCP server built into router Ethernet giải điều chế thành IP, UDP thành DHCP

DHCP: example DHCP DHCP server formulates DHCP ACK containing client’s IP address, IP address of first-hop router for client, name & IP address of DNS server DHCP UDP IP Eth Phy encapsulation of DHCP server, frame forwarded to client, demuxing up to DHCP at client DHCP UDP IP Eth Phy DHCP DHCP router with DHCP server built into router client now knows its IP address, name and IP address of DSN server, IP address of its first-hop router DHCP

Ghi chú: Address Pools Leases (Thuê) Client’s request Lease duration: minutes or days Client’s request requested lease duration, a copy of the address it is already using or last used, and other parameters Server’s response Based on client’s information (including the requesting MAC address) in addition to other exogenous information (e.g., the time of day, the interface on which the request was received)

DHCP/BOOTP Message Format

Some options Common options include Pad (0) Subnet Mask (1) Router Address (3) Domain Name Server (6) Domain Name (15) Requested IP Address (50) Address Lease Time (51) DHCP Message Type (53) Server Identifier (54) Parameter Request List (55) DHCP Error Message (56) Lease Renewal Time (58) Lease Rebinding Time (59) Client Identifier (61) Domain Search List (119) End (255).

Protocol Operation The IPv6 header is of fixed size (40 bytes) and contains 128-bit source and destination addresses. The Next Header field is used to indicate the presence and types of additional extension headers that follow the IPv6 header, forming a daisy chain of headers that may include special extensions or processing directives. Application data follows the header chain, usually immediately following a transport-layer header.

DHCP Message Types T: Lease Time T1: Renewal Time: start renewal with same server after this time expires Typically T/2 T2: Rebinding Time: renewal must be done with same server by T2. If not, then rebinding of the address is needed which means doing it from scratch while indicating that the client already has an IP address (in the client addr) Typically 7T/8

Lease Timers: An Example (tcpipguide.com)

DHCP client state machine

IPv6 Address Lifecycle Tentative: can be used only for IPv6 Neighbor Discovery DAD: Duplicate Address Detection is performed in this state Optimistic: It is like Tentative, but an address is allocated for some limited use Deprecated: can be used for existing connections, but not for new connections DAD: Duplicate Address Detection

Duplicate Address Detection (DAD) send one or more ICMPv6 Neighbor Solicitation messages If a Neighbor Advertisement message is received in response, DAD has failed, and the address being checked is abandoned

DHCPv6

Location Information GEOCONF option(“Geographical configuration”) Latitude, longitude, altitude GEOCONF_CIVIC option Country, city, district etc. More complex as the categories vary by country and characters in different languages have complex representations Why are these options needed?

Mobility and Handoff Information DHCP options to convey information about cellular configuration and handovers between different networks Types of such options Information Services available networks Command Services functions for controlling link parameters Event Services notification of link status changes

DHCP Snooping Implemented in some switches which limits DHCP traffic to those addresses that are in a list Two problems can be potentially addressed Rogue DHCP server is limited in the damage it can do Allocation limited to a set of MAC addresses

Stateless Address Autoconfiguration (SLAAC) Consider a network that has a single link and suppose there are no DHCP servers Single-Link or Link Local Addresses Automatic Private IP Addressing Generate a random address (169.254.1.1 through 169.254.254.254 using the 16-bit subnet mask 255.255.0.0) Check for conflicts using ACD (Address Conflict Detection)