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Computer Networks > IPv4 Multicasting and IPv6 Introduction > Flashcards

IPv4 Multicasting and IPv6 Introduction Flashcards

1
Q

Multicasting

A

Packets routed from source to multiple destinations

  • Key for group communication
  • Address identifies a group Not widely used for now.
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2
Q

IPv4 Multicast Addressing

A

Class D addresses

  • Begin with 111O → 224.O.O.O - 239.255.255.255
  • Group delivery delegated to lower level (MAC)
  • IP multicast address mapped to a MAC multicast address: 0x01005E U 0x1b U 23 LSBs of IP address
  • Interface card configured to receive that MAC multicast
  • Recipient initiated group join
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3
Q

Routers in IPv4 Multicasting

A

Routers role:

  • Routers discover host groups on each LAN
    • Internet Group Management Protocol (IGMP)
  • Routers announce host groups to others
    • Multicast routing protocols
  • Routers build a distribution tree foreach host group
    • To all LANs with at least a member
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4
Q
A
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5
Q

State of deployment of IPv4 Multicast

A
  • Not widely supported
  • Not fit to common traffic engineering practices
  • Mostly limited to controlled environments
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6
Q

Why IPv6?

A
  • Larger address space
  • More effiecient on LANs
  • Multicast and anycast
  • Security
  • Policy routing
  • Plug and Play
  • Traffic differetiation
  • Mobility
  • Quality of service support
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7
Q

IPv4 usable addresses and why we need more of them

A

Only 3.5M addresses can be used

Those 3.5M can be used hierearchically

  • The prefix used in a physical network cannot be used into another
  • Lots of unused addresses
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8
Q

Interim IPv4 solutions to the saturation of address space

A
  • Taylored sized network => NETMASK
  • Private addresses
    • Intranet, however not enough. It should be used in conjuction with NAT or ALG.
  • NAT
    • Very popular
    • Proposal for RSIP
  • ALG: Application Level Gateway
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9
Q

Routing scalability issues of IPv4

A
  • Routing table size
    • Internet size
    • each subnetwork must be advertised
  • Problems
    • Router resource limitations
    • Too much info to manage
    • Routing protocols limitations
    • High probability of route changes (for backbone routers)
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10
Q

Routing scalability solutions in IPv4

A

Aggregate multiple routes into one:

  • Short prefix including others
  • CIDR (Classless inter-domain routing)
  • Limited by non-rational assignment of IP prefixes

Limit the assignement of IP addresses:

  • Regional Internet Registry: assign address blocks only to big players.

Scalability of routing protocols:

  • No solution, at present. Still open also for IPv6
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11
Q

Addressing efficiency

A

H = log10(number of adresses) / number of bits

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12
Q

Addressing space organization of IPv6

A
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13
Q

Address structure IPv6

A

With subnet prefixes having no more than 64bits

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14
Q

Subnet ipv6

A

set of hosts with same prefix

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15
Q

Link ipv6

A

Physical network

subnetwork === link

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16
Q

On-link hosts

A

Have same prefix and communicate directly

17
Q

Off-link station

A

Different prefixes → communicate through router

18
Q

Link local

A

frist bits are 1111 1110 10

Si riferiscono agli indirizzi privati “automatici”, generati dall’autoconfigurazione, che è il processo in cui una stazione genera automaticamente un indirizzo per connettersia un link IPv6.

19
Q

Site local

A

Is deprecated function that is equivalent to ipv4 private addresses.

frist bits are 1111 1110 11

20
Q

Global Unicast Aggregatable

A
  • Equivalent to public IPv4 addresses.
  • They start with 3 bits: 001
  • Topology-based assignement:
    • Service provider hierarchy
    • Effective aggregation
21
Q

Global Univast Addressing Space Organization

A

IPv4 Mapped addresses

  • 80 bits to 0, 16 bits to 1 then the IPv4 address: 0:0:0:0:0:ffff:A00:1
  • To be used during transition phase

IPv4 compatible addresses

  • 96 bits to 0 then IPv4 address: 0:0:0:0:0:0:A00:1
  • Spacial notation: ::10.0.0.1
  • Deprecated
22
Q

Plug And Play

A

Scenarios:

  • Dentist office
  • Thousand computers on the dock

Solution: autoconfiguration:

  • Stateless: no server needed
  • Stateful: DHCP server
23
Q

IPv6 Special addresses

A
  • Loopback: ::1
  • All nodes (multicast) FF02::1
  • All routers (multicast) address FF02:2
  • Unspecified address: ::
24
Q

Changed and upgraded protocols in IPv6

A

Changed:

  • IP
  • ICMP
  • ARP: Integrated in ICMP
  • IGMP: integrated in ICMP

Upgraded:

  • DNS
  • RIP and OSPF
  • BGP and IDRP
  • TCP and UDP
  • Socket interface
25
Q

Socket API

A
  • Programming interface for TCP/IP services
  • Used in application implementation (UDP messages and byts on TCP connections)
  • Socket descriptor is equivalent to a file descriptor (pointer) for network resources
  • Associated to UPD/TCP session/connection
  • Server listens (listen()) for requests on a port and accepts requests
  • Client connects to port of remote server, send/receive data.
26
Q

IPv6 Packet header format

A
  • Many fields removed respsect to IPv6
    • Not useful, no longer needed, not used in each packet
27
Q

Extension Header Format

A

Extension headers:

  • used when useful, not needlessly processed in each packet
  • Hop by hop option: options that each router has to evaluate
  • destination option: options only for destination
  • Type-Length-Value Format

Extension header must be 64bits aligned:

  • Pad1 Option: Type:0
  • PadN Option: Type:1 Len:0-6 Value: 0-6 bytes
28
Q

Routing HEADER

A
  • Used to list nodes to travers on the path to destination (loose or strict)
  • Segment Left Field show the number of remaining path segments
29
Q

IPv6 Encapsulation

A

Encapsulated in layer 2 frames (EtherType: 86DD): new protocol that enables dual stack (IPv4 as is + IPv6)

30
Q

IPv6 address mapping to MAC

A

IP unicast address:

  • Procedural: protocol based (Neighbor discovery)

IP multicast address:

  • algorithmic mapping

IPv6 multicast trasmission:

  • Based on MAC multicast
  • MAC A.: 33-33 | 4 LSBytes of IPv6 Address
    • Example: FFOC::89:AABB:CCDD → 33:33:AA:BB:CC:DD
31
Q

Neighbor discovery

A

New function in ICMP that replaces ARP, based on multicast, but most likely only one station gets involved.

Host Cache === ARP cache

Process

  1. FF02::1:FF/104 | LSbits of IPaddr (Mulicast address) is solicited through Neighbor solicitation
  2. Encapsuted in MAC frame to 33:33:FF | LSbits of IPaddr
  3. Likely is just 1 host per group
  4. ICMP Neighbor Advertisement to petitioner
32
Q

Transition to IPv6

A

Isolated IPv6 networks -> islands grow -> ipv6 native connectivity -> doomsday

All protocols specified since 1996

Implemented on routers, maybe less stable than ipv4.

Hardware implementation on Layer 3 switch.

Implemented on Windows since 2000, also on GNU/Unix ecosystem.

When will it happen?

When there will not be anymore addresses, but the issue is being mitigated (provident address assignment, use of private addressing, NAT, proxying)

Acceptable limitation so far:

  • user traceability
  • Not many public addresses for servers
  • NAT not suitable for all applications

Computer Networks (12 decks)

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