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CNCT > IPv6 > Flashcards

IPv6 Flashcards

1
Q

Why IPv6?

A

larger address space
+
security
multicast and anycast
more efficiente on LANs
mettere policy routing and traffic differentiation
QoS support

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1
Q

How do you transform 1A3 in decimal?

A

116^2 + A16 + 3

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2
Q

Which are the differences in the network structures of IPv4 and IPv6?

A

IPv6 has not net mask or classes but it has a prefix -> address/n where n is the length of the prefix

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3
Q

How many bits the IPv6 prefix have?

A
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4
Q

Which is the IPv6 schema of the possible address types? (no ranges)

A

multicast
- well-known
- transient
- solicited-NODE

unicast
- global UNICAST
- link local
(- site local)
- LOOPBACK
- unique LOCAL
- undefined
- EMBEDDED IPv4

anycast

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5
Q

What is a IPv6 subnet?

A

a set of hosts that have the same prefix and that are in the same physical network

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6
Q

Which is the general characteristic of the IPv6 address for multicast address?

A

is starts with eight 1 so FF00::/8 is the general address -> 2^120 MULTICAST ADDRESSES

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7
Q

Which are the characteristics of IPv6 multicast addresses and what they’re made of?

A
  • well know: FF00::/12, predefined or reserved to group of devices. ASSIGNED BY IANA
  • transient: FF10::/12, they a re used for the classical multicast so they identify a group, dynamically assigned by multicast apps
  • Solicited node: FF02:0:0:0:0:FF00:0/104 -> SIMILAR TO IP BROADCAST IN ARP. IT IS CONSTRUCTED BY TAKING THE LOWER 24 BITS OF A UNICAST OR ANYCAST ADDRESS AND BY APPENDING IT TO THAT PREFIX

the third digit is the flag:
- FF0… permanent, BY IANA
- FF1… dynamic

the fourth digit is the scope:
- FFx1: INTERFACE LOCAL: ONLY FOR INTERFACES
- FFx2: LINK-LOCAL: JUST INSIDE THE LOCAL NETWORK, IT CANNOT BE ROUTED BY THE ROUTER
- FFx5: SITE-LOCAL: CAN ONLY BE FORWARDED BY THE ROUTER TO LINKS THAT ARE DIRECTLY ATTACHED TO IT
- FFx8: ORGANIZATION-LOCAL: ONLY FORWARDED TO OTHER ROUTER THAT ARE OF THE SAME ORGANIZATION
- FFxE: GLOBAL: IT CAN BE GLOBALLY FORWARDED

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8
Q

In which types of addresses the IPv6 unicast group is divided? (6)

A
  • link local
  • loopback
  • unique local
  • global unicast
  • UNSPECIFIED
  • embedded ipv4
    (site-local)
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9
Q

IPv6: global unicast addresses

A

They identify globally an host AND THEY ARE ASSIGNED WITH PLUG AND PLAY. THEY ARE. EQUIVALENT TO IPV4 PUBLIC ADDRESSES

THEY START WITH 001

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10
Q

IPv6: link local addresses

A

FE80::/64

When a device enters a network it automatically get a link local address but it cannot be routed OUTSIDE so if it arrives to the router it cannot forward it.

THEY CAN ONLY BE ROUTED IN A SINGLE ROUTING DOMAIN

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11
Q

IPv6: site local addresses

A

FEC0::/10

NONE COULD AGREE ON WHAT A SITE WAS SO THEY WERE NEVER USED

DEPRECATED

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12
Q

IPv6 multicast addresses range

A

FF00::/8 in general

  • FF00::/12 well known
  • FF10::/12 transient
  • FF02:0:0:0:0:FF00:0/104 solicited nodes
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13
Q

IPv6 unicast addresses ranges

A
  • link local
  • loopback
  • unique local
  • global unicasst
  • undefined
  • embedded ipv4
    (site-local)
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14
Q

IPv6: unique local addresses

A

= PRIVATE IPV4 ADDRESSES

FC00::/7 MADE OF
1111 1101 + 40 RANDOMLY GENERATED BITS + 16 BITS FOR THE SUBNET IDS + 64 BIT FOR THE INTERFACE

They. cannot be routed outside but they can be routed from a private network. to another -> THEY MUST BE ROUTED ONLY IN PRIVATE. LINKS

THEY CAN BE DUPLICATED IN DIFFERENT ORGANIZATIONS (E ALLORA COME FANNO AD ANDARE DA UNA NET A UN’ALTRA???) BUT HAVE TO BE UNIQUE IN A NET

THEIR 8TH BIT IS THE LOCAL FLAG:
- 1: THE ADDRESS IS LOCALLY ASSIGNED
- 0: IT MAY BE DEFINED IN THE FUTURE OR IT CANNOT BE ASSIGNED??

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15
Q

IPv6: IPv4 embedded addresses

A

::/80

The first 80 bits are 0
+
16 bits FFFF
+
32 bits with the IPv4 address

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16
Q

IPv6: loopback addresses

A

They are identified by the address ::1 that is equivalent to 127.0.0.1 of IPv4

They are used by a node for testing reasons to send a packet to itself.

A packet that has this address cannot go out of the network, cannot be assigned to a physical interface, if anode receives a packet and the destination is a loopback address it should drop it

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17
Q

IPv6: unspecified addresses

A

They are all 0s and they are used as source addresses to indicate the absence of and address

They are used in the Duplicate Address Detection (DAD) in ICMPv6

they cannot be assigned to an interfaces as the. loopback ones

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18
Q

IPv6 anycast addresses

A

the range is not written in the slides

They can be assigned to more than one interface and the packet will be forwarded to the nearest one according to the router’s routing table

Designed for DNS but work in progress

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19
Q

Which are the main differences between a IPv4 header and an IPv6 one

A

Removed fields:
- header checksum: check done in L2 and L4
- Header length: now it is fixed, 40 B
- Fragmentation: a packet cannot be bigger than the MTU because IPv6 doesn’t perform fragmentation (eventually only the SOURCE can do it by using the Fragmentation Header)

New fields:
- Next header: chain of headers to specify protocols and or options
- payload length

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20
Q

Which IPv4 field were removed from the IPv6 header?

A

Removed fields:
- header checksum: check done in L2 and L4
- Header length: now it is fixed, 40 B
- Fragmentation: a packet cannot be bigger than the MTU because IPv6 doesn’t perform fragmentation (eventually only the SOURCE can do it by using the Fragmentation Header)

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21
Q

Which are the new IPv6 header fields?

A

New fields:
- Next header: chain of headers to specify protocols and or options
- payload length

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22
Q

List some of the possible extension headers

A
  • Hop by Hop extension header
  • Fragmentation extension header
  • AH and ESP extension header
  • Routing extension header
23
Q

Hop-by-hop extension header

A

If it is present it is after the first header and it specifies some options that each router (next hop)will have to know.
Each option is made of TLV triplets:
- Option Type
- Option length
- Option value

24
Q

Routing extension header

A

When the source wants the packet to follow a special path and not the one indicated by the routing tables -> SOURCE ROUTING

25
Q

Fragment extension header

A

Fragmentation is possible only when performed by the source router that fragment the packet and each packet will have its own header + FRAGMENT EXTENSION HEADER

The receiver will reassemble everything

26
Q

AH and ESP extension headers

A

IPsec

27
Q

Why 128 bits

A

to have H = [log_10(number of addresses)] / number of bits

H in (0.14, 0.26)

28
Q

Which is the IPv6 schema of the possible address types? + address ranges

A

multicast
- well-known: FF00::/12
- transient: FF10::/12
- solicited-NODE: FF02:0:0:0:0:1:FF00::/104

unicast
- global UNICAST: THEY START WITH 001 BUT 2000::/3
- link local: FE80::/10
(- site local)
- LOOPBACK: ::1/128
- unique LOCAL: FC00::/7
- undefined
- EMBEDDED IPv4: ::/80

anycast

29
Q

How si a MAC address found in IPv6?

A

If it is a multicast address we do a mapping, if it is a unicast one we use the Neighbor Discovery procedure

30
Q

How is a MAC address found in IPv6 for a multicast address?

A
  1. we have a multicast address
  2. we take its 32 LSBs
  3. we append them to 33-33
  4. the 7th bit (or 8???) is 1 -> multicast
31
Q

How is a MAC address found in IPv6 for a unicast address?

A
  1. the target address (the one we want to reach) is a global unicast
  2. we create its Solicited Node multicast by taking the last 24 bits of the global unicast address and by appending them to FF02::1:FF00:0/104
  3. we get the corresponding multicast MAC
  4. we send our request using these destinations: multicast MAC + Solicited Node Multicast
  5. the router of the multicast group hopefully will send the message only to the target host
  6. the target will send back its MAC address
32
Q

Why do we use ICMPv6?

A
  • diagnostics
  • neighbor discovery
  • multicast group management
  • issue notification
  • functions that in ipv4 were done for example from ARP or IGMP
33
Q

How is a ICMP message composed? What is its maximum size? Next header number

A

576 B

Next Header = 58

8 8 16
type - code - checksum
message body

34
Q

Which are the most important type fields an ICMP message? Explain in brief for what are they used

A

code < 128: error
destination unreachable, packet too big, time exceeded, parameter problem, …

code > 128: informational messages
- echo request and reply
- Neighbor solicitation and advertisement -> Neighbor discovery
- router solicitation and advertisement -> to obtain the address prefix
- redirect
- multicast listener query and report: to perform multicast group management

35
Q

Which fields a ICMP message for parameter problem has?

A

8 8 16
type - code - checksum
message body

message body = parameter + header of the IP packet that generated the problem

36
Q

Which fields a echo ICMP message has?

A

8 8 16
type - code - checksum
message body

message body = identifier + sequence number + data

37
Q

Which fields a Neighbor Solicitation and Advertisement ICMP messages have and how do they work?

A

Neighbor Solicitation
8 8 16
type - code - checksum
message body

message body = reserved + target address + options

  • It is encapsulated in a IPv6 packet that has IP destination = Solicited Node Multicast Address
  • The IPv6 packet is encapsulate in a L2 frame that has Mac destination= multicast MAC
  • ## The target address is a tag that tells if the packet was delivered to the right recipient and that is. because Solicited Node Multicast address do not guarantee that the address is unique because they differ only for their last 24 bits -> ICMP has to check it (DAD??)

Neighbor Advertisement
8 8 16
type - code - checksum
message body

message body = reserved + target address + options + flags (R, S, O)

-if it is sent in response a solicitation -> S=1 (solicited flag)
- if it is sent autonomously -> S = 0.

It is sent autonomously when the host changes its IP address. and wants to advertise about this -> for this we have the Override Flag (O):
- O = 1: IP changed
- O = 0: no

38
Q

how does the “Multicast Group Management” ICMP function work? Which are the related ICMP messages?

A

Within a link = in a subnet : it is done with the layer 2 and the mapping of IPv6 multicast addresses - multicast MAC

Among links = among subnets : ICMP is used to know which are the on-link hosts and the off-link hosts -> hosts interested in receiving packets

Messages:
- multicast listener query: it can be general or specific. If it is general it is sent to all the groups connected to the router interfaces (almost broadcast)
- multicast listener report
- multicast listener Done

39
Q

Which fields a Multicast Listener Query/Report/Done ICMP messages have?

A

8 8 16
type - code - checksum
message body

message body = maximum response delay + multicast address + unused

40
Q

How can a IPv6 node be configured?

A
  • manually
  • stateful -> DHCP
  • stateless
  • hybrid: prefix stateless and other infos with DHCP

These solutions come from the decisions on how to get the prefix and the interface id

41
Q

How can we get a IPv6 interface ID?

A
  • manually
  • stateful -> DHCP
  • stateless -> automatic
42
Q

How does the automatic configuration of a IPv6 address identifier work?

A

We use the Extended Unique Identifier EUI-48 = MAC address
->
OUI (from EUI-48) + 0xFF+ 0xFE + serial number (from EUI-48)
and then
opposite of the 7th bit

43
Q

Which is the problem with getting the interface ID in an automatic way? (IPv6) Which is the solution?

A

If a device always uses an interface ID that directly comes from its MAC address this is not secure because of the possible traceability -> an attacker only has to know the prefix of the network (public) and the MAC

Solution: Privacy Extension for STATELESS ADDRESS AUTOCONFIGURATION IN IPV6

???

44
Q

In which case do we need a Privacy Extension?

A

Witch the stateless address auto configuration in IPv6

45
Q

How can we get a IPv6 prefix?

A
  • manually
  • stateful -> DHCP
  • stateless -> automatic
  • from a router -> ICMP function -> Router advertisement and solicitation
46
Q

Which fields a Router Solicitation and Advertisement ICMP messages have and how do they work?

A

Router Solicitation
8 8 16
type - code - checksum
message body

message body = reserved + options

  • It is sent by the host who wants to discover if there is a router in its network and which gateway to use in order to reach it
  • ## this message is sent to all the router that have te multicast address FF01::2

Router Advertisement
8 8 16
type - code - checksum
message body

It can be sent in response or autonomously.

message body =
- Router Lifetime
- Reachable Time
- Retransmission Timer
- M: Managed Address Configuration. If it is 1 it means that the router has not been configured and cannot tell the prefix -> the host will have to ask to DHCP
- O (Other Configuration): if M = 1 but the host has to ask someone different from DHCP
- Options: in the TLV format, max 8 B. Some of the options are: Prefix Information, MTU, Link Layer Address

47
Q

What is a Prefix Information Option?

A

It is one of the possible options that can be used in the “Options” field of a Router Advertisement message (discovery of the address prefix).

It is a TLV.

Principle flags:
- L (on-link flag): 1 if the prefix its used on this link, 0 if it is used on other links that the router has access to
- A: 1 if the prefix can be used for autonomous configuration, 0 to tell a specific prefix to an host

48
Q

What is a MTU Option?

A

It is one of the possible options that can be used in the “Options” field of a Router Advertisement message (discovery of the address prefix).

It is a TLV.

Ensures that all the hosts on a link has the same MTU if the fragmentation is enabled

49
Q

What is a Link Layer Address Option?

A

It is one of the possible options that can be used in the “Options” field of a Router Advertisement message (discovery of the address prefix).

It is a TLV.

It is used by routers to tell their connected hosts which is their MAC to avoid performing Neighbor Discovery

50
Q

Which fields a Redirect ICMP messages have and how does it work?

A

Router Solicitation
8 8 16
type - code - checksum
message body

message body = reserved + target address (the host to reach) + destination address (next-hop) + options

When a ROUTER receives a packet for a destination but there is a better next hop it send back that packet saying to update the routing table

Redirect Header Option ?pagina 43

51
Q

What is DAD for IPv6?

A

Duplicate Address Detection

This mechanism its used to probe the uniqueness of an IPv6 address

ci sono scritte altre coe che non capisco pagina 43

52
Q

ved pagina 44 ipv6

A
53
Q

Why do we need scoped addresses in IPv6?

A

Because a multi interfaces host can have the same link local address for all those interfaces.
This creates a. problem when applications do not know which socket should. they send data to

54
Q

How is a scoped address composed?

A

IPv6 address + % + number that identifies the interface
-> 17 B instead of 16 B

The scope number is seen only at upper layers, never on the link -> internal identification

55
Q

manca ipv6 routing

A
56
Q

manca ipv4 - ipv6 transition

A

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