internet working session i
TRANSCRIPT
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Inter-Networking Session I
2nd September 2008
Presented by Michuki Mwangi
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Topics
IP and Networking Basics
DNS Fundamentals
Contention Ratio
Monitoring and Measurement Tools
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IP and Networking Basics
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Outline
Origins of TCP/IP
OSI & TCP/IP Architecture
IPv4 Addressing
IPv6 Routing
Types of Links
Address Resolution Protocol
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Origins of TCP/IP
RAND Corporation (a think tank) & DoDformed ARPA (Advanced Research ProjectAgency)
1968 ARPA engineers proposed Distributednetwork design for ARPANET Network
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A small internetwork or (small i)
internet
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The (capital I) Internet
The world-wide network of TCP/IP networks
Different people or organisations own differentparts
Different parts use different technologies
Interconnections between the parts
Interconnections require agreements sale/purchase of service transit agreements
Contracts and SLAs
peering agreements
No central control or management
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The principle of Internetworking
We have lots of little networks
Many different owners/operators
Many different types
Ethernet, dedicated leased lines, dialup, ATM, Frame Relay,
FDDI
Each type has its own idea of addressing andprotocols
We want to connect them all together and provide aunified view of the whole lot (treat the collection of
networks as a single large internetwork)
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What is TCP/IP?
In simple terms is a language that enablescommunication between computers
A set of rules (protocol) that defines how two
computers address each other and send datato each other
Is a suite of protocols named after the twomost important protocols TCP and IP; butincludes other protocols such as UDP, RTP,etc.
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Protocol Layers:
The TCP/IP Hourglass Model
Network layer
Token
RingATM X.25 PPP
Frame
RelayHDLCEthernet
IP
UDPTCP
HTTP FTP Telnet DNSSMTP Audio Video
RTP
Data link layer
Transport layer
Application layer
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Corresponding layers in the
OSI and TCP/IP models
TCP/UDP end to end reliability
IP - Forwarding (best-effort)
Framing, delivery
Raw signal
Mail, Web, etc.
1
3
2
4
5
6
7 Application
Presentation
SessionTransport
Network
Data Link
Physical
Application
Transport
Network
Data Link &
Physical
OSI TCP/IP
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IP Addressing
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Purpose of an IPv4 address
Unique Identification of:
Source
So the recipient knows where the message is from
Sometimes used for security or policy-based filtering of
data
Destination
So the networks know where to send the data
Network Independent Format
IP over anything
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Purpose of an IPv4 Address
Identifies a machines connection to a network
Physically moving a machine from onenetwork to another requires changing the IP
address Unique; assigned in a hierarchical fashion
IANA to RIRs (AfriNIC, ARIN, RIPE, APNIC,LACNIC)
RIR to ISPs and large organisations
ISP or company IT department to end users
IPv4 uses unique 32-bit addresses
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133 27 162 125
10000101 00011011 10100010 01111101
85 1B A2 7D
Basic Structure of an IPv4 Address
32 bit number (4 octet number):(e.g. 133.27.162.125)
Decimal Representation:
Binary Representation:
Hexadecimal Representation:
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Addressing in Internetworks
The problem we have
More than one physical network
Different Locations
Larger number of computers
Need structure in IP addresses
network part of the address identifies whichnetwork in the internetwork (e.g. the Internet)
host part identifies host on that network
Hosts or routers connected to the same link-layernetwork will have IP addresses with the samenetwork part, but different host part.
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Hierarchical Division in IP Address:
Network Part (Prefix) high order bits (left)
describes which physical network
Host Part (Host Address) low order bits (right)
describes which host on that network
Boundary can be anywhere
very often NOT at a multiple of 8 bits
choose the boundary according to number of hosts
Network Host
205 . 154 . 8 1
11001101 10011010 00001000 00000001
Address Structure Revisited
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Network Masks
Network Maskshelp define which bits areused to describe the Network Part and whichfor the Host Part
Different Representations: decimal dot notation: 255.255.224.0 binary: 11111111 11111111 11100000 00000000
hexadecimal: 0xFFFFE000
number of network bits:/19
count the 1's in the binary representation
Binary AND of 32 bit IP address with 32 bitnetmask yields network part of address
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137.158.128.0/17 (netmask 255.255.128.0)
198.134.0.0/16 (netmask 255.255.0.0)
205.37.193.128/26 (netmask 255.255.255.192)
Example Prefixes
1000 1001 1001 1110 1 000 0000 0000 0000
1111 1111 1111 1111 1 000 0000 0000 0000
1100 0110 1000 0110 0000 0000 0000 0000
1111 1111 1111 1111 0000 0000 0000 0000
1100 1101 0010 0101 1100 0001 10 00 0000
1111 1111 1111 1111 1111 1111 11 00 0000
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Special Addresses
All 0s in host part: Represents Network
e.g. 193.0.0.0/24
e.g. 138.37.128.0/17
All 1s in host part: Broadcast e.g. 137.156.255.255 (137.156.0.0/16)
e.g. 134.132.100.255 (134.132.100.0/24)
e.g. 190.0.127.255 (190.0.0.0/17)
127.0.0.0/8: Loopback address (127.0.0.1)
0.0.0.0: Various special purposes
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Allocating IP Addresses
The subnet mask is used to define size of anetwork
E.g. a subnet mask of 255.255.255.0 or /24means 24 network bits, 8 host bits(24+8=32)
28 minus 2 = 254 possible hosts
Similarly a subnet mask of 255.255.255.224or /27 means 27 network bits, 5 host bits(27+5=32)
25 minus 2 = 30 possible hosts
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More levels of address hierarchy
We can also group several networks into alarger block, or divide a large block intoseveral smaller blocks
arbitrary number of levels of hierarchy
blocks dont all need to be the same size
but each block size must be a power of 2
Old systems used restrictive rules (obsolete)
Called Class A, Class B, Class C networks
These days (since 1994), no restriction
Called classless
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A little History:
Classes of IP addresses
Different classes were used to represent differentsizes of network (small, medium, large)
Class A networks (large):
8 bits network, 24 bits host (/8, 255.0.0.0)
First byte of IP address in range 0-127 Class B networks (medium):
16 bits network, 16 bits host (/16 ,255.255.0.0)
First byte of IP address in range 128-191
Class C networks (small):
24 bits network, 8 bits host (/24, 255.255.255.0)
First byte of IP address in range 192-223
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Netmasks of classful addresses
A classful network had a natural or impliedprefix length or netmask:
Class A: prefix length /8 (netmask 255.0.0.0)
Class B: prefix length /16 (netmask 255.255.0.0)
Class C: prefix length /24 (netmask 255.255.255.0)
Modern (classless) routing systems haveexplicit prefix lengths or netmasks
You can't just look at an IP address to tell what the
prefix length or netmask should be. It needs explicit
configuration.
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Traditional subnetting of classful
networks
Old routing systems allowed a classfulnetwork to be divided into subnets
All subnets (of the same classful net) had to be thesame size and have the same netmask
Subnets could not be divided into sub-sub-nets
None of these restrictions apply in modernsystems
You should never use old routing systems that
have these restrictions (e.g. RIP version 1)
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Classless Addressing
Class A, Class B, Class C terminology andrestrictions are now of historical interest only Obsolete in 1994
Internet routing and address management
today is classless CIDR = Classless Inter-Domain Routing
routing does not assume that class A, B, C impliesprefix length /8, /16, /24
VLSM = Variable-Length Subnet Masks routing does not assume that all subnets are the
same size
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Classless addressing example
A large ISP gets a large block of addresses e.g., a /16 prefix, or 65536 separate addresses
Allocate smaller blocks to customers e.g., a /22 prefix (1024 addresses) to one
customer, and a /28 prefix (16 addresses) toanother customer
An organisation that gets a /22 prefix fromtheir ISP divides it into smaller blocks e.g. a /26 prefix (64 addresses) for one
department, and a /27 prefix (32 addresses) foranother department
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IPv6
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IP version 6
IPv6 designed as successor to IPv4
Expanded address space
Address length quadrupled to 16 bytes (128 bits)
Header Format Simplification
Fixed length, optional headers are daisy-chained
No checksum at the IP network layer
No hop-by-hop fragmentation
Path MTU discovery
64 bits aligned fields in the header
Authentication and Privacy Capabilities
IPsec is mandated
No more broadcast
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IPv4 and IPv6 Header ComparisonIPv4 Header IPv6 Header
Fields name kept from IPv4 to IPv6
Fields not kept in IPv6
Name and position changed in IPv6
New field in IPv6
Legend
Next
Header
Hop Limit
Flow LabelTraffic Class
Destination Address
Source Address
Payload Length
Version
FragmentOffset
Flags
Total LengthType ofService
IHL
PaddingOptions
Destination Address
Source Address
Header ChecksumProtocolTime toLive
Identification
Version
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Larger Address Space
IPv4 32 bits
= 4,294,967,296 possible addressable devices
IPv6 128 bits: 4 times the size in bits
= 3.4 x 1038
possible addressable devices = 340,282,366,920,938,463,463,374,607,431,768,211,456
5 x 1028 addresses per person on the planet
IPv4 = 32 bits
IPv6 = 128 bits
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16 bit fields in case insensitive colon hexadecimalrepresentation 2031:0000:130F:0000:0000:09C0:876A:130B
Leading zeros in a field are optional: 2031:0:130F:0:0:9C0:876A:130B
Successive fields of 0 represented as ::, but only oncein an address: 2031:0:130F::9C0:876A:130B is ok
2031::130F::9C0:876A:130B is NOT ok (two ::)
0:0:0:0:0:0:0:1 ::1 (loopback address)
0:0:0:0:0:0:0:0 :: (unspecified address)
IPv6 Address Representation
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IPv6 Address Representation
In a URL, it is enclosed in brackets (RFC3986)
http://[2001:db8:4f3a::206:ae14]:8080/index.html
Cumbersome for users
Mostly for diagnostic purposes
Use fully qualified domain names (FQDN)
Prefix Representation
Representation of prefix is same as for IPv4 CIDR
Address and then prefix length, with slash separator
IPv4 address:
198.10.0.0/16
IPv6 address:
2001:db8:12::/40
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IPv6 Addressing
::/12800000000Unspecified
::1/12800000001Loopback
FF00::/81111 1111 ...Multicast Address
FC00::/71111 1100 ...
1111 1101 ...
Unique Local
Unicast Address
FE80::/101111 1110 10...Link Local
Unicast Address
2000::/30010 ...Global Unicast
Address
HexBinaryType
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Interface IDGlobal Routing Prefix Subnet-id
001
64 bits48 bits 16 bits
Provider Site Host
IPv6 Global Unicast Addresses
IPv6 Global Unicast addresses are:
Addresses for generic use of IPv6 Hierarchical structure intended to simplify
aggregation
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2000 0db8
ISP prefix
Site prefix
LAN prefix
/32 /48 /64
Registry
/12
Interface ID
IPv6 Address Allocation
The allocation process is: The IANA is allocating out of 2000::/3 for initial IPv6
unicast use
Each registry gets a /12 prefix from the IANA
Registry allocates a /32 prefix (or larger) to an IPv6 ISP
Policy is that an ISP allocates a /48 prefix to each endcustomer
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IPv6 Addressing Scope
64 bits reserved for the interface ID
Possibility of 264 hosts on one network LAN
Arrangement to accommodate MAC addresseswithin the IPv6 address
16 bits reserved for the end site
Possibility of 216 networks at each end-site
65536 subnets equivalent to a /12 in IPv4(assuming 16 hosts per IPv4 subnet)
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IPv6 Addressing Scope
16 bits reserved for the service provider
Possibility of 216 end-sites per service provider
65536 possible customers: equivalent to eachservice provider receiving a /8 in IPv4 (assuming a
/24 address block per customer)
32 bits reserved for service providers
Possibility of 232 service providers
i.e. 4 billion discrete service provider networks
Although some service providers already are justifyingmore than a /32
Equivalent to the size of the entire IPv4 addressspace
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Summary
Vast address space
Hexadecimal addressing
Distinct addressing hierarchy between ISPs,
end-sites, and LANs ISPs have /32s
End-sites have /48s
LANs have /64s
Other IPv6 features discussed later
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Routing
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Routing and Forwarding
Routing is not the same as Forwarding
Routing is the building of maps Each routing protocol usually has its own routing
database
Routing protocols populate the forwarding table Forwarding is passing the packet to the next
hop device Forwarding table contains the best path to the next
hop for each prefix
There is only ONE forwarding table
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IP Routing
Each router or host makes its own routing decisions
Sending machine does not have to determine the entire path to
the destination
Sending machine just determines the next-hop along the path
(based on destination IP address)
This process is repeated until the destination is reached, or theres
an error
Forwarding table is consulted (at each hop) to determine the
next-hop
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IP Routing
Classless routing
route entries include
destination
next-hop
mask (prefix-length) indicating size of address space described by the
entry
Longest match
for a given destination, find longest prefix match in the routing table
example: destination is 35.35.66.42
routing table entries are 35.0.0.0/8, 35.35.64.0/19 and 0.0.0.0/0
All these routes match, but the /19 is the longest match
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IP routing
Default route
where to send packets if there is no entry for the
destination in the routing table
most machines have a single default route
often referred to as a default gateway
0.0.0.0/0
matches all possible destinations, but is usually not the
longest match
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Static vs. Dynamic routing
Static routes
Set up by administrator
Changes need to be
made by administrator Only good for small
sites and star topologies
Bad for every other
topology type
Dynamic routes
Provided by routing
protocols
Changes are madeautomatically
Good for network
topologies which have
redundant links (most!)
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Dynamic Routing
Routers compute routing tables dynamicallybased on information provided by otherrouters in the network
Routers communicate topology to each other
via different protocols Routers then compute one or more next hops
for each destination trying to calculate themost optimal path
Automatically repairs damage by choosing analternative route (if there is one)
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A Large ISP with more than oneupstream provider
UpstreamISP
UpstreamISP
Africa
Europe
USA
Large ISP
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Why does an ISP need BGP?
Multi-homing connecting to multipleproviders
upstream providers
local networks regional peering to get local traffic
Policy discrimination controlling how traffic flows
do not accidentally provide transit to non-customers
Aggregation
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Defining BGP
BGP = Border Gateway Protocol
BGP is an exterior routing protocol
Focus on routing policy, not topology
BGP can make groups of networks(Autonomous Systems)
Good route filtering capabilities
Ability to isolate from others problems
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BGP Protocol Basics
Routing Protocol used between
ASes
If you arent connected to
multiple ASes you dont needBGP
Runs over TCP
AS 100 AS 101
AS 102
EE
BB DD
AA CC
Peering
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BGP Protocol Basics
Uses Incremental updates
sends one copy of the RIB at the beginning, then
sends changes as they happen
Path Vector protocol
keeps track of the AS path of routing information
Many options for policy enforcement
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Terminology
Transit carrying network traffic across a network, usually for a
fee
Peering exchanging routing information and traffic
your customers and your peers customers network information only.
not your peers peers; not your peers providers.
Peering also has another meaning:
BGP neighbour, whether or not transit is provided
Default where to send traffic when there is no explicit route in
the routing table
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What is an Exchange Point
Network Access Points (NAPs) established at
end of NSFnet
The original exchange points
Major providers connect their networks andexchange traffic
High-speed network or ethernet switch
Simple concept any place where providers
come together to exchange traffic
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Internet Exchange Points
ISPs connect at Exchange Points or NetworkAccess Points to exchange traffic
IXP 1 IXP 2
ISP A
ISP B
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Conceptual Diagram of an IXP
ISP Router
ISP Router
ISP Router
Exchange Point Medium
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Why use an IXP?
KEEP LOCAL TRAFFIC LOCAL!!!
ISPs within a region peer with each other at the
local exchange
No need to have traffic go overseas only to come
back
Much reduced latency and increased performance
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Why use an IXP?
VASTLY IMPROVES PERFORMANCE!!!
Network RTTs between organisations in the local
economy is measured in milliseconds, not seconds
Packet loss becomes virtually non-existent
Customers use the Internet for more products,
services, and activities
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Why use an IXP?
Countries or regions with a successful IXP
have a successful Internet economy
Local traffic stays local
Money spent on local net infrastructure Service Quality not an issue
All this attracts businesses, customers, and
content
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Domain Name System(DNS) Fundamentals
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Computers use IP addresses.Why do we need names?
Names are easier for people to remember
Computers may be moved betweennetworks, in which case their IP address
will change.
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The old solution: HOSTS.TXT
A centrally-maintained file, distributed to allhosts on the Internet
SPARKY 128.4.13.9
UCB-MAILGATE 4.98.133.7
FTPHOST 200.10.194.33
... etc
This feature still exists:/etc/hosts (UNIX)
c:\windows\hosts
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hosts.txt does not scale
Huge file (traffic and load)Name collisions (name uniqueness)
Consistency
Always out of date
Single point of Administration
Did not scale well
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The Domain Name System was born
DNS is a distributed database for holdingname to IP address (and other) information
Distributed:
Shares the Administration
Shares the Load
Robustness and improved performanceachieved through
replication
and caching
Employs a client-server architecture
A critical piece of the Internet'sinfrastructure
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DNS is Hierarchical
.(root)
ke org com
DNS Database
/ (root)
etc usrbin
Unix FilesystemForms a tree structure
ac.ke
kcct.ac.ke
isoc.org afnog.org google.com
www.isoc.org
usr/local usr/sbin/etc/rc.d
usr/local/src
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DNS is Hierarchical (contd.)
Globally unique names Administered in zones (parts of the tree)
You can give away ("delegate") control ofpart of the tree underneath you
Example: isoc.org on one set of nameservers
wiki.tools.isoc.org on a different set
elists.isoc.org on another set
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Domain Names are (almost) unlimited
Max 255 characters total length
Max 63 characters in each part RFC 1034, RFC 1035
If a domain name is being used as a host name,
you should abide by some restrictions RFC 952 (old!)
a-z 0-9 and minus (-) only
No underscores ( _ )
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Using the DNS
A Domain Name (like www.isoc.org) is theKEY to look up information
The result is one or more RESOURCERECORDS (RRs)
There are different RRs for different types ofinformation
You can ask for the specific type you want,or ask for "any" RRs associated with thedomain name
Commonly seen Resource Records
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Commonly seen Resource Records(RRs)
A (address): map hostname to IPv4 address AAAA (quad A): map a hostname to IPv6
address
PTR (pointer): map IP address to hostname
MX (mail exchanger): where to deliver mail for
user@domain
CNAME (canonical name): map alternative
hostname to real hostname
TXT (text): any descriptive text
NS (name server), SOA (start of authority):used for delegation and management of the
DNS itself
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A Simple Example
Query: www.isoc.org.Query type: A
Result:
www.isoc.org. 86400 IN A 206.131.241.137
In this case a single RR is found, but ingeneral, multiple RRs may be returned.
(IN is the "class" for INTERNET use of the
DNS)
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Possible results from a Query
POSITIVEone or more RRs found
NEGATIVE
definitely no RRs match the query
SERVER FAIL cannot find the answer
REFUSED
not allowed to query the server
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How DNS resolution works (2)
ResolverCaching
NS
Query
1
AuthNS
2
Auth
NS
3
AuthNS
4Response
5
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DNS Resolving and Caching
Resolver
Caching Forwarder
(Recursive)
Root Server
ccTLD Server
KENIC Server
www.my.co.ke A?
www.my.co.ke A?
www.my.co.ke A?
www.my.co.ke A?
62.8.88.72
Ask .ke server @
mzizi.kenic.or.ke (+glue)
Ask kenic server @
ole.kenic.or.ke (+glue)
62.8.88.72
Add to
Cache
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Contention Ratio
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Definition
The ratio of the potential maximum demand (usage)to the actual bandwidth available - ref wikipedia
Also referred to as Overbooking ratio
Call it the bandwidth sharing ratio
Most service providers do not disclose this ratio In the UK its 50:1 on BT home ADSL and 20:1 on
business subscribers
The ratio is higher in the US - re Comcast case
No Data on Kenyan ISPs contention ratio
Argument for contention ratio is that 10% ofsubscribers utilize over 80% of bandwidth available
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What does it mean?
In the ratio of 50:1 it means if you have a1Mbps link you are most likely sharing such(transit) with 49 other subscribers.
Therefore if all users were online
simultaneously you would get a speed of20Kbps
The easiest way to observe downloads at peakhours and off-peak hours
Also locally hosted content would be subjectto lower content ratios
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Monitoring and MeasurementTools
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Why Monitoring is important
To check network health status
Identify network bottlenecks
Plan for growth and expansion
Address security issues
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Open Source Monitoring tools
MRTG & Cacti for bandwidth utilization
Nagios for service monitoring
Smokeping for RTT and availability
FlowD, NFSEN for protocol analysis and utilization
Webalizer - Web-server log monitoring
Rancid - router management
Snort - intrusion detection
Wireshark - tcdump analysis and log file
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Open Source Measurement Tools
Ping - one-way RTT and reachability
Traceroute - one-way reachability
Mtr - one-way path attributes, packet loss,
Netperf- client/server bandwidth,throughput
Iperf- client/server bandwidth, throughput
Pathchar - one-way bandwidth, through put
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Iperf sample
michuki:~ michuki$ iperf -c wavu.kixp.or.ke------------------------------------------------------------Client connecting to wavu.kixp.or.ke, TCP port 5001TCP window size: 65.0 KByte (default)------------------------------------------------------------[ 3] local 10.0.1.2 port 62134 connected with 80.240.194.142 port 5001[ ID] Interval Transfer Bandwidth[ 3] 0.0-13.6 sec 232 KBytes 139 Kbits/sec
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Netperf
michuki:~ michuki$ sudo netperf -H wavu.kixp.or.ke -f kPassword:
TCP STREAM TEST to wavu.kixp.or.keRecv Send SendSocket Socket Message ElapsedSize Size Size Time Throughputbytes bytes bytes secs. 10^3bits/sec
65536 65535 65535 27.35 54.64
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82/82
Thank you for your attention!
Most of the slides used are lifted from the AfNOG training material
available at:
www.ws.afnog.org