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content/notes/11-DHCP.md
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@ -14,6 +14,14 @@ Address Assignment
- Allow direct network booting - Allow direct network booting
- Like RARP, constrained to single subnet, but perform at UDP/IP, instead of MAC layer - Like RARP, constrained to single subnet, but perform at UDP/IP, instead of MAC layer
> [!INFO] RARP
> given mac address it finds the ip address. the opposite of ARP
> [!INFO] ARP
> we need arp because we need the data link layer protocol. so we need the destination mac address. this allows us to send ethernet frame to a MAC address
> [!INFO] BOOTP
DHCP DHCP
- Dynamic Host Configuration Protocol (DHCP) - Dynamic Host Configuration Protocol (DHCP)
- Compatible with BOOTP (uses same ports) - Compatible with BOOTP (uses same ports)
@ -23,6 +31,13 @@ DHCP
- Limited to a single subnet, but routers can incorporate relay agents - Limited to a single subnet, but routers can incorporate relay agents
- Successor: DHCPv6, less useful in IPv6 - Successor: DHCPv6, less useful in IPv6
> [!INFO] DHCP
> more widely used. more compatible and generalised
> gives not only address. also tell you what is DNS server and gateway.
> ubiquitious
> radvd and slacc similar to DHCPv6
> send broadcast message to network. the server takes these broadcast messages and returns and IP address, and the lease time of the address. broadcaster sends another messages to accept/reject the offer. this sequence of messages has a session ID
Static vs. Dynamic Static vs. Dynamic
- Static address is assigned manually by system admin in the DHCP configuration file using the client’s MAC address - Static address is assigned manually by system admin in the DHCP configuration file using the client’s MAC address
- Server machines’ addresses should be static - Server machines’ addresses should be static
@ -30,6 +45,8 @@ Static vs. Dynamic
- Dynamically allocated address can be assigned to the same client as it keeps a table of past IP addresses and their clients MAC addresses. - Dynamically allocated address can be assigned to the same client as it keeps a table of past IP addresses and their clients MAC addresses.
- Layer 3 (IP) change breaks existing connections if IP addresses change in a long session such as downloaders, terminal sessions - Layer 3 (IP) change breaks existing connections if IP addresses change in a long session such as downloaders, terminal sessions
> [!INFO]
How DHCP Works How DHCP Works
- Client broadcasts UDP request to 255.255.255.255 port 67 - Client broadcasts UDP request to 255.255.255.255 port 67
- Routers can relay using a relay agent - Routers can relay using a relay agent
@ -106,3 +123,14 @@ S.D. with DHCP
- Requires client support, in DHCP client or application - Requires client support, in DHCP client or application
- You can provision based on the machine or subnet, or a single group - You can provision based on the machine or subnet, or a single group
S.D. with DNS-SD
- Service (SRV) records specify service type, transport protocol, and the domain.
- _smtp._tcp.domain returns Priority, Weight, Port and Address of mail servers, for browsing.
- DNS Service Discovery (DNS-SD) allows for browsing service instances.
- Most commonly used with mDNS.
- Not suitable for very dynamic data in traditional DNS. Why?
DNS-SD Example
- Examples taken from draft DNS-SD standard.
- What services are available on dns-sd.org? (provides a discovery starting point) dig +short -t any _services._dns-sd._udp.dnssd.org _ftp._tcp.dns-sd.org. _ssh._tcp.dns-sd.org. (and others...)
- What FTP services are available on dnssd.org? dig +short -t any _ftp._tcp.dnssd.org Apple\032QuickTime\032Files._ftp._tcp.d ns-sd.org. (and others...)