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Internet Systems > Week 3 TCP/IP > Flashcards

Week 3 TCP/IP Flashcards

1
Q

What differentiates TCP/IP networks (week 3) from other weeks work?

A

Previous weeks have focused on LAN. TCP/IP looks at WAN - the Internet. Internet = Network layer 2

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2
Q

What is IP?

A

Internet Protocol:
- Connectionless service
- Network addressing
- Best effort
- Routing tables (OSPF/RIP)
- Fragmentation and reassembly of packets

IPv4 address example:
32 bits represented by dot notation: 138.77.45.3
Part of the bits represent the LAN, the other part represent the host inside the LAN

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3
Q

What classes of address are there?

A
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4
Q

What is subnet addressing?

A

Splitting the network for containment and faster routing -> i.e. one path has 1.1.0.0 and the other has all 1.2.0.0 addresses

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5
Q

What is different about IPv6 vs IPv4?

A

IPv6 offers:
An expansion of IP addresses
Hierarchical IP addresses
IPsec function
QOS control function
No fragmentation
Automatic allocation of IP addresses
Simplified header
Allows jumbograms (very big packets)

4 groups of digits: 128.40.42.82

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6
Q

What are IPv6 address blocks?

A

Blocks of ipv6 are formed so as to create segregated groups - these groups can have specific features such as:
- A limited multicast address space (note there is no broadcast in IPV6)
- A limited local unicast address space
- Local address blocks
- Global unicast (2000::/3)
- Special case unicast address (anycast)

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7
Q

How are IPv6 addresses allocated?

A

Designed to result in efficient routing tables.
1. Assignment are hierarchical with the Regional Internet Regristries getting large /12 allocations
2. /48 prefix are allocated to organisations and private individuals
3. Very large organisations may be assigned a /47 or a set of /48 prefixes
4. Recommendation is to use 64 bits for network part and 64 bits for host part
5. Host part is then derived using 48 bit MAC address padded to 65 bits

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8
Q

How do you identify a multicast address in IPv6?

A

A multicast address is indicated by FF in first byte.
FF02::1 = All nodes on a link
FF02::2 = All routers on a link
FF05::2 = All routers in a site
FF05::3 = All DHCP servers in a site

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9
Q

How are multicast addresses mapped to ethernet?

A
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10
Q

What is the Address Resolution Protocol (ARP)? (Given an IP address, what is the MAC address?)

A
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11
Q

What is the Address Resolution Protocol over a network on the internet?

A
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12
Q

What is the ARP equivalent process for IPv6?

A
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13
Q

How do you obtain your own IP address (IPv4/IPv6)?

A

IPv4=Dynamic Host Configuration Protocol (DHCP)
- Broadcast a message to discover DHCP
- Server eventually replies with default router, netmask, dns server to configure yourself

IPv6=StateLess Address AutoConfiguration (SLAAC)
- On host boot it binds each network interface to the following adddresses::
1. FF02::1 multicast
2. ::1 Loopback address
3. FF02::1:ffxx:xxxx node solicitation multicast address (xx part = mac address)
4. FE80::Inteface id
To access beyond LAN, host must then search for routers on the network. A router soliciation message is sent to all-routers multicast address (FF02::2) - each one replies with a router advertisement.
Host can then use DAD (Duplicate Address Detection) to construct a neighbour discovery packet to find if there is a node using the same address. For security, computer will also pick a series of bits randomly and fill in the last 48 btis randomly.

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14
Q

How is fragmentation done in IPv4/IPv6?

A

In IPv4 the message is fragmented by routers and defragmented by end systems. The packet will contain a fragment offset to describe which section it is.
In IPv6 no fragmentation exists. Messages are sent using Path MTU discovery - it sends a packet, if a link drops the packet because the packet is too big, it sends an ICMP message back to the host to alert them. The host then retries until it succeeds.

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15
Q

What is Internet Control Message Protocol (ICMP)?

A

ICMP is used by IP to send error and control messages. Can be sent by end hosts or routers. In IPv6 ICMP also is used for router and host configuration. Methods used:
PING - to see whether an IP address is reachable
TRACEROUTE - send packets with different time to live to determine how far it is.

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16
Q

What is Network Address Translation (NAT)?

A

Sometimes an ISP may have many more computers than IP addresses, so NAT is used to convert a private IP to a public IP.
Problems that can arise:
port exhaustion - some applications use lots of tcp connections.

17
Q

What is Mobile IP?

A

Nodes move to a different network but still want the packets destined to their “old” address.
1. Agent Discovery
- Router periodically broadcasts or multicasts ICMP RD (router discovery) messages on all its links.
2. Registering
- The mobile sends a registration request, the foreign agent then relays this request to the home agent, the home agent accepts or denies the request, the foreign agent relays this reply to the mobile node.
3. Tunnelling
- Until now the home agent arrived at a foreign network…it discovered a router willing to act as a foreign agent and registered with its home agent.
- So we send an IP over an IP (nested IP) with the inner layer being the original message content and the outer layer the new destination.
- Tunnelling refers to any carrying of lower level traffic in higher (or equal) layers - think VPNs, IPV4 inside IPV6 etc.

In IPv6 the triangle problem (slow path between the mobile and home nodes) is resolved. The IPv6 packet can contain Destination options to tell the node where it is, so any future data transfer is more efficient.

18
Q

What are IPv4 Options?

A

THe IP packet header contains a field (of variable size) that allows for extract options:
1. Record Route
2. Time stamp
3. Loose source route
4. Strict source route
5. Router alert

19
Q

What are IPv6 Extension headers?

A

Alike IPv4 options, but more of them.
1. Routing header (for source routing)
2. Fragment header (indicates the packet got fragmented)

20
Q

How does the internet deal with IPv4 and IPv6 routing?

A

Not all routers can be upgraded to IPv6 immediately, so both exist. Two appraoches used:
1. Dual stack: some routers can “translate” between formats
2. Tunneling: IPv6 carrying IPv4 data

Internet Systems (7 decks)

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