Content

Dynamic Host Configuration Protocol (DHCP)
Network Address Translation (NAT)
Internet Control Message Protocol (ICMP)
IPv6
1. Header
2. Backward Compatibility
  1. Dual Stack
  2. Tunneling/Encapsulation

Dynamic Host Configuration Protocol (DHCP)

Dynamically obtain IP address from network server upon joining the network.

Discover: broadcast UDP DHCP discover packet
- If no nearby server, need a DHCP relay agent to forward the request to known server
Offer: respond with UDP DHCP offer packet
- Answers registered MAC addresses OR assign IPs from a pool
- yiaddr: the assigned IP
Request: broadcast UDP DHCP request packet
- Requested IP = returned yiaddr
Ack: respond with UDP DHCP ack packet
- Ack the leasing of the IP
- Host get:
  - IP
  - Leasing duration T
    - T1 = 0.5T, attempts renew of lease (request)
    - T2 = 0.875T, no reply, broadcast request to any server
    - No reply by T, relinquish IP & start over
  - Router's IP
  - Subnet mask
  - DNS info
  - Hostname, domain, ...

One IP to the outside world of a local network -> fix not enough IPv4 addresses.

Additional advantages
- Change IP of devices in local network without notifying outside world
- Change ISP without notifying devices in local network
- Security, local devices not exposed to outside world
Implementation
- Outgoing packets
  - Replace (source IP, source port) with (NAT IP, new port) -> WAN side address
  - Recalculate checksum
  - Records mapping in NAT
- Incoming packets
  - Replace (NAT IP, new port) with source IP, source port -> LAN side address
Problems
- Port numbers are meant for addressing processes, not hosts
- Routers are supposed to process packets up to layer 3
- Violates end-to-end argument: hosts should talk directly to each other without interfering devices modifying IP & ports
- P2P applications should be explicitly aware of the existance of NAT
- Some applications pass IP & port in commands; changing TCP/IP headers is not enough
- IPv6 should be the solution
NAT traversal problems
- Client wants to connect to server behind NAT
  - Statically configure NAT to forward incoming requests at given port to server
Private IP addresses
- 10.0.0.0/8
- 172.16.0.0/12
- 192.168.0.0/16

Encapsulated in IP datagram.

Error reporting
- Unreachable host/network/port/protocol
- Message contains IP header & first 8 bytes of error datagram
Echo request/reply (ping)
Report TTL=0 (tracert)

128 bit
- 8 groups of 16-bit, HEX, colons between
- IPv4 to IPv6: ::FFFF:x.x.x.x/128
Fixed-sized header; improved option mechanism
- Simplified header, routers can process packets faster
Mechanism of autoconfiguration of network interfaces
Supports resource allocation; enhance QoS support
Fragmentation at source node
- Avoid fragmentation at internal nodes to speed up performance
Built-in authentication & encryption
No checksum
- Transport & link layers already done so
- Avoid recomputation of checksums due to TTL changes
Hierarchical addressing rather than address classes (i.e. CIDR-like)
Types
- Unicast: uniquely identifies an interface of a device
- Multicast: an address reaching a group of interfaces
- Anycast: assigned to a group of interfaces of a common address
  - Packets sent to the nearest one
  - Created automatically when a unicast address is assigned to > 1 interfaces

Traffic class & flow label: support QoS; priority
Payload length: how many bytes follow this header
Hop limit: TTL
Next header
- Points to the extension/option headers OR transport protocol data follow this one
- Extension headers are daisy chained & ordered
- Most of the cases, fixed-sized headers can streamline packet processing in routers
- Extension headers needed to be examined by intermediate routers will be listed first; no need to scan through all extension headers