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CS 455 > Network Layer: Data Plane > Flashcards

Network Layer: Data Plane Flashcards

1
Q

IP Addressing

IPv4

A

32-bit identifier associated with each host/router interface

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2
Q

IP Addressing

Interface

A
  • Connection between host/router and physical link
  • Each interface has its own IP address
  • Routers have multiple interfaces (and therefore multiple IP addresses)
  • Host has one or two interfaces
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3
Q

IP Addressing

Subnet

A

Device interfaces that can physically reach each other wo passing through an intervening router

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4
Q

IP Addressing

IP Address Structure

A

Subnet Part: devices in same subnet have common high order bits
Host Part: remaining low order bits

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5
Q

IP Addressing

Subnet Mask

A

Divides the subnet part of the IP address from the host part

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6
Q

IP Addressing

CIDR

A
  • Classless InterDomain Routing
  • Subnet portion of address has arbitrary length
  • Address Format: a.b.d/x, where x is the # of bits in the subnet portion
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7
Q

IP Addressing

How does a host get an IP address?

A
  • hard-coded by sysadmin in config file
  • DHCP gets address from server
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8
Q

IP Addressing

DHCP

A
  • Dynamic Host Configuration Protocol
  • Dynamically obtain IP address from network server when it joins the network
  • can renew lease on address in use
  • allows reuse of addresses (only hold address while connected)
  • support
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9
Q

DHCP

DHCP Steps

A
  1. host broadcasts DHCP discover message (optional)
  2. DHCP server responds with DHCP offer message (optional)
  3. host requests IP address with DHCP request message
  4. DHCP server sends address with DCHP ACK message
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10
Q

DHCP

DHCP Broadcast

A
  • Optional
  • Sent by client
  • Asks if there are any DHCP servers
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11
Q

DHCP

DHCP Offer

A
  • Optional
  • Sent by DHCP server
  • Tells client that its a DHCP server and sends an avaliable IP address
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12
Q

DHCP

DHCP Request

A
  • Required
  • Sent by client
  • Asks DHCP server to use offered IP address
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13
Q

DHCP

DHCP ACK

A
  • Required
  • Sent by DHCP server
  • Sends confirmation to client that it has the IP address it requested
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14
Q

DHCP

What can DHCP server return?

A
  • Allocated IP address
  • Address of first-hop (closest) router for client
  • Name and IP address of DNS server
  • Network mask/subnet mask (indicating network vs host portion of address)
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15
Q

Network Address Translation

NAT

A
  • Network Address Translation
  • All devices in local network share just one IPv4 address as far as the outside world is concerned
  • All datagrams leaving local network have same souce NAT IP address
  • All datagrams inside local network have IP address containing subnet mask
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16
Q

Network Address Translation

Private IP Address Examples

A
  • 10.
  • 172.
  • 192.168
17
Q

Network Address Translation

Private IP Address Advantages

A
  • Only one IP address needed from ISP for all devices
  • Can change addresses of host in local network wo notifying outside world
  • Can change ISP without changing addresses of devices in local network
  • Security: devices inside local network not directly addressable/visible by outside world
18
Q

Network Address Translation

Private IP Address

A

IP address that’s assigned to a device by a network router for use within a private network.

19
Q

Network Address Translation

NAT Implementation

A
  • Outgoing datagrams: replace (src IP, port#) of every outgoing datagram to (NAT IP, new port #)
  • Remember (in NAT table) every (src IP, port #) to (NAT IP, new port #) translation pair
  • Incoming datagrams: replace (NAT IP, new port#) in dest fields of every incoming datagrams with corresponding (src IP, port #) in NAT table
20
Q

IPv6

IPv6 Motivation

A
  • 32-bit IPv4 address space has been completely allocated
  • Faster processing/fowarding (40 byte fixed length header)
  • Enable different network-layer treatment of flows
21
Q

IPv6

IPv6 Datagram Format

A
  • priority: identify priority amount datagrams in flow
  • 2 128-bit addresses, dest and src
  • flow label: identify datagrams in same flow
  • no checksum, fragmentation/reassembly, or options
22
Q

IPv6

Tunneling

A
  • Transition from IPv4 to IPv6
  • IPv6 datagram carried as payload in IPv4 datagram among IPv4 routers (packet in a packet)
  • usually, datagram is payload in link-layer frame but here in IPv4 datagram
  • source/dest changes to start/end of IPv4 router path
23
Q

Generalized Forwarding

Forwarding Table

A
  • a.k.a flow table
  • Contained in router
  • Used to determine routes to reach destinations
24
Q

Generalized Forwarding

Match Plus Action

A

Abstaction matching bits in arriving packet to action

25
Q

Generalized Forwarding

Destination-Based Forwarding

A

Forward based on dest IP address

26
Q

Generalized Forwarding

Generalized Forwarding

A
  • Many different header fields can determine action
  • Many actions possible
27
Q

Generalized Forwarding

Possible Actions

A

Actions resulting from header fields:
* Drop
* Copy
* Modify
* Log packet

28
Q

Generalized Forwarding

Flow

A
  • What actions correspond to what header fields?
  • Defined by header field values
29
Q

Generalized Forwarding

Generalized Forwarding Rules

A

Match: pattern values in packet header fields
Actions: for matched packet, choose action
Counters: # of bytes and # of packets

30
Q

Generalized Forwarding

OpenFlow

A
  • match+action: abstraction unifies between different kinds of devices
  • Routers, Switches, Firewall, and NAT
31
Q

Generalized Forwarding

OpenFlow: Routers

A

match: longest dest IP prefix
action: forward out a link

32
Q

OpenFlow: Switch

A

match: dest MAC address
action: forward or flood

33
Q

Generalized Forwarding

OpenFlow: Firewall

A

match: IP addresses and TCP/UDP port #s
action: permit or deny

34
Q

Generalized Forwarding

OpenFlow: NAT

A

match: IP address and port
action: rewrite address and port

CS 455 (11 decks)

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