diff --git a/content/notes/11-DHCP.md b/content/notes/11-DHCP.md new file mode 100644 index 000000000..bd1ff4c95 --- /dev/null +++ b/content/notes/11-DHCP.md @@ -0,0 +1,108 @@ +--- +title: "11-DHCP" +tags: +- lecture +- cosc301 +--- + +Address Assignment +- First there was Reverse ARP (RARP) + - Only IP address, no options for DNS etc. +- Then the Bootstrap Protocol (BOOTP) + - Included concept of tagged options + - Useful for software like X-Terminals, + - Allow direct network booting + - Like RARP, constrained to single subnet, but perform at UDP/IP, instead of MAC layer + +DHCP +- Dynamic Host Configuration Protocol (DHCP) +- Compatible with BOOTP (uses same ports) +- Can efficiently use a shared pool of addresses +- IP addresses can be tied to MAC address, or client IP name +- Ubiquitous (at least in the IPv4 sense!) +- Limited to a single subnet, but routers can incorporate relay agents +- Successor: DHCPv6, less useful in IPv6 + +Static vs. Dynamic +- 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 +- Dynamically allocated addresses have a lease time period before they are re-assigned + - 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 + +How DHCP Works +- Client broadcasts UDP request to 255.255.255.255 port 67 + - Routers can relay using a relay agent +- The first DHCP server may send an offering + - Corollary: there should usually only be one DHCP server in a subnet (broadcast zone) +- Offer can contain many types of options. + - Netmask, default router, DNS server, lease time, etc. + - https://tools.ietf.org/html/rfc2132 + +DHCP client/server source code +- https://github.com/samueldotj/dhcp-client +- https://www.oryxembedded.com/doc/dhcp__server_8c_sourc e.html +- https://github.com/isc-projects/dhcp + +Manual Assignment vs. DHCP +- Of course, you could do it manually. Why? + - PRO Protection against multiple/rogue DHCP servers! + - CON Change management + - PRO / CON: Better control, but bigger problems when mistakes are made, e.g., IP address clash +- DHCP is still fairly reliable. + - Short outages are generally unnoticeable + +Ad-hoc Assignment +- ZeroConf (Zero Configuration Networking) Link Local Addresses + - 169.254.0.0/16 + - Single subnet, no routing (no internet) +- Get an address by selecting an address and testing for duplicates +- Useful for ad-hoc networks, and unconfigured network devices +- Similar to the principle of IPv6 link local addresses + +Service Offerings +- Network configuration + - Current offerings like DHCP are suitable +- Service location and configuration + - Current offerings/support not enough +- E.g. name resolution service for ad-hoc network + - How to find a web proxy or email gateway in an institute? + - Should services should be resolved or searched based on Physical Location? Network Location? User? Class? Device? + +Ad-hoc Name Resolution +- IP traditionally lacks this + - Proprietary LAN-based protocols have supported it for years + - AppleTalk, NetBIOS +- Useful when infrastructure has no local knowledge (e.g. no DNS) +- In IP world: Multicast DNS (mDNS) + +Multicast DNS +- mDNS queries are the same as DNS, except queries are targeted at 224.0.0.251:5353 + - Queries are made under ‘.local’, so ‘.local’ should never be used for traditional DNS + - .local. + - Client resolvers must recognise .local queries + - Special treatment: not upstream DNS +- Also Microsoft’s LLMNR (Link-Local Multicast Name Resolution) + + +Service Discovery +- Locate the services we need automatically, or by browsing, searching/filtering or provisioning + - Indistinct services all behave the same way and can be assigned automatically + - Distinct services provide different behavior and need to browsed, searched, or provisioned +- Need to consider network context + - Operates within a specified network scope +- Many protocols were proposed for service discovery + - DNS-SD in Zero Configuration Networking, DHCP options, SLP, Directory Services like LDAP + +Well known service names +- http://wpad.domain/wpad.dat for Web proxy auto-configuration +- Other common names include smtp (or mail), pop3, imap, ftp, www, ns1, ns2, time + - These should be aliases, so they can be redirected to other machines easily +- Most useful for human-based configuration + +S.D. with DHCP +- DHCP has various, diverse options: Syslog, DNS, LPR, WINS, NTP, LDAP (!) + - Think carefully about security +- Requires client support, in DHCP client or application +- You can provision based on the machine or subnet, or a single group + diff --git a/content/notes/cosc-301.md b/content/notes/cosc-301.md index c2c113197..6acd913da 100644 --- a/content/notes/cosc-301.md +++ b/content/notes/cosc-301.md @@ -41,7 +41,7 @@ https://www.cs.otago.ac.nz/cosc301/schedule.php - [x] [[09-wireless-networking]] - [x] [[10-scheduled-tasks-and-logs]] - [ ] [[11-DNS]] need to read about security -- [ ] +- [ ] [[11-DHCP]] # Info diff --git a/content/notes/cosc-342.md b/content/notes/cosc-342.md index 5f20a31d7..42eaa754a 100644 --- a/content/notes/cosc-342.md +++ b/content/notes/cosc-342.md @@ -28,7 +28,6 @@ tags: - [[08-visual-tracking-and-matching]] - [x] [[09-3d-geometry]] - [x] [[10-3d-Cameras]] -- [ ] # Info diff --git a/content/notes/cosc-342.sync-conflict-20230404-150341-OX6NNIH.md b/content/notes/cosc-342.sync-conflict-20230404-150341-OX6NNIH.md new file mode 100644 index 000000000..5f20a31d7 --- /dev/null +++ b/content/notes/cosc-342.sync-conflict-20230404-150341-OX6NNIH.md @@ -0,0 +1,34 @@ +--- +title: "cosc-342" +year: 2023 +semester: 1 +tags: +- course +- +--- +# Assignments + +- [ ] [[342-assignment-01]] + +# Labs + +- [x] [[01a-getting-started]] +- [x] [[01b-cpp-essentials]] +- [ ] [[02-image-transforms]] + +# Notes + +# Lectures +- [x] [[01-intro-to-342]] +- [x] [[02-colour-representation]] +- [x] [[03-2d-transforms]] +- [[04-mosaicing]] +- [x] [[05-feature-description-and-matching]] +- [x] [[06-homographies]] +- [[08-visual-tracking-and-matching]] +- [x] [[09-3d-geometry]] +- [x] [[10-3d-Cameras]] +- [ ] + +# Info +