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Since 2007 GOFORTUTION.coM is the search engine of tutors & Students in Delhi and all over India .It provides cheapest and best home tutors to students and it also helps to Tutors who are seeking ...

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    gofortution gofortution Presentation Transcript

    • IP Addressing and Introduction to IP routing Avgust Jauk <jauk@arnes.si> ARNES Bratislava, August 98
    • Agenda
      • Internet topology
      • Introduction to addressing
      • Idea of routing
      • Special address conventions
      • Classfull addressing
      • Classless addressing
      • Routing protocols: IGPs and EGPs
    • Internet topology
      • Internet - Network of Networks
      • Networks
        • Based on different technology
        • Large or small
        • Fast or slow
        • Variety of connected nodes
      • Routers (Gateways)
      • Protocols
    • Internet topology
    • Routers
      • Packet handling
      • Packet forwarding
      • Routing information processing
      • Management
      • Miscellaneous functions
    • Internet protocol stack
    • Internet protocol dependencies Hardware Users
    • Internet protocol dependencies Hardware Users
    • Layering in the Internet Application Transport Internet Network interface Application Transport Internet Network interface Internet Network interface Identical message Identical packet Identical datagram Identical datagram Identical frame Identical frame Physical Net 1 Physical Net 2 Gateway G Host A Host B
    • Internet datagram format
    • ICMP datagram format
    • ICMP Message types Type Field ICMP Message Type 0 Echo Reply 3 Destination Unreachable 4 Source Quench 5 Redirect (change a route) 8 Echo Request 11 Time Exceeded for Datagram 12 Parametere Problem on a Datagram 13 Timestamp Request 14 Timestamp Reply 15 Information Request (obsolete) 16 Information Reply (obsolete) 17 Address Mask Request 18 Address Mask Reply
    • Introduction to addressing
      • Do I need an address?
      • What types of addresses are there?
        • Postal address
        • Telephone number
        • In Computer Networks:
          • Physical Addresses (Ethernet, FDDI, ...)
          • Textual Addresses - Names
          • Network level addresses (IP, X.25,...)
    • Addressing in the Internet
      • Address specifies host’s interface
      • 32 bit addresses
      • Network part & Host part
      • Dotted decimal notation: 192.164.2.4
      Network part Host part 0 31
    • Idea of routing
      • Routers forward datagrams between connected networks
      • They need to know via which interface to send a datagram
      • Routing decisions are based on the information stored in the routing table
    • Routing table
      • Tells where to send datagram for a particular network
      Network Next-Hop Port Metric 194.181.200.0 194.181.208.1 Eth0 1 193.2.1.0 194.181.208.320 Eth1 14 153.5.0.0 194.181.214.25 Fddi0 8 0.0.0.0 194.181.210.1 S0 5
      • Next-Hop routers must be directly reachable
    • Routing table (cont.)
      • Default Route - a special entry in the routing table:
        • “ Pass all datagrams for unknown networks to this router”
        • Represented by the entry for network 0.0.0.0
      • Routing uses network part of the address!
    • Routing Algorithm
      • Extract destination IP address from datagram
      • Extract network address from the IP address
      • If destination network equals my network
        • Send directly to destination using physical network
      • Else If destination address matches a host-specific route in the routing table:
        • Send to the router specified in the routing table
    • Routing Algorithm (cont.)
      • Else if destionation network matches a network in the routing table
        • Send to the router specified in the routing entry
      • Else If there is a default route in the routing table:
        • Send to the router specified in the default route entry
      • Else:
        • Send a “No route to host” message to the source
    • Populating the Routing Table
      • Manually by network administrator: Static Routes
        • No dynamic changes to these routes will accur
      • Dynamically by routing protocol
        • Routing info is exchanged between routers
        • The routing “metric” is used to find the best path
    • Static Routes Manually configured by network administrator A B
    • Static Routes Router cannot automatically reroute if path fails A B
    • Routing protocols
      • Routers use a common protocol to exchange routing information
      • Best path between networks or subnets is determined by “Routing Metric”
      • Automatic adaption to topology changes
    • Routing protocols 64 kbps 64 kbps 2 Mbps 2 Mbps
    • Special address conventions
      • Broadcast Addresses
        • Directed broadcast: host part all 1’s - 194.181.200.255
        • Limited broadcast: all 1’s - 255.255.255.255
      • 0 means “This”
        • host part = 0 - this host
        • network part = 0 - this network
        • miss used as a broadcast address
    • Special address conventions (cont.)
      • Loopback Address : 127.0.0.1
        • for testing and inter-process communication on the local machine
        • should never appear on any network
    • Summary of special address conventions This host Limited broadcast (local net) Host on this net Directed broadcast for net Loopback all 0s all 0s host all 1s net 127 anything (often 1) all 1s
    • Classess and address formats 0 1 2 3 4 8 16 24 31 netid netid hostid hostid multicast address reserved for future use Class A Class C Class D Class E 0 0 0 0 netid hostid Class B 0 1 1 1 1 1 1 1 1 1 1
    • Classes: How to recognize them
      • Class A: first byte in range 1-126
      • Class B: first byte in range 128-191
      • Class C: first byte in range 192-223
      • Class D: first byte in range 224-239
      • Class E: first byte in range 240-255
    • Classes: Size and Number
      • Class A: 16.777.214 hosts, 128 networks
      • Class B: 65.534 hosts, 16.324 networks
      • Class C: 254 hosts, 2.097.152 networks
    • Problems with Classes
      • Class A usually to big
      • Class C often to small
      • Not enough Class Bs
      • Inefficient utilisation of address space
      • Solution: extending the network part of the address: Subnetting
    • Subnetting Class B 0 1 Class B 0 1 Class B Address: Before Subnetting Class B Address: After Subnetting Network Network Host Host Subnet
    • Subnet mask
      • Subnet mask defines the network part
        • binary 1 in network bits
        • binary 0 in hosts bits
      • Subnet mask must be contiguous!
      Network part Host part 0 31 1 ..... 1 0 ...... 0
    • Subnetting (cont.)
      • Not limited to byte border
      • Subnets “0” and “-1” used to be reserved
        • Subnet “0” : this subnet
        • Subnet “-1”: broadcast
      • Network administrator decides on the subnet size
      • Network and subnet numbers used for routing decisions
    • Subnetting and routing
      • one subnet mask per particular class
      • routing considerations
        • all subnets of the same class must be contiguous
        • or static routes must be used
        • or routing protocol must carry also subnet masks
    • Subnetting and routing
      • all subnets of the same class must be contiguous!
      C 1 1 C 1 2 B C 1 4 C 1 3 C 1 C 1
    • Subnet mask bits 128 64 32 16 8 4 2 1 1 0 0 0 0 0 0 0 = 128 1 1 0 0 0 0 0 0 = 192 1 1 1 0 0 0 0 0 = 224 1 1 1 1 0 0 0 0 = 240 1 1 1 1 1 0 0 0 = 248 1 1 1 1 1 1 0 0 = 252 1 1 1 1 1 1 1 0 = 254 1 1 1 1 1 1 1 1 = 255
    • Binary Numbers = 128 + 64 + 32 + 2 128 64 32 16 8 4 2 1 Represent 226 decimal in binary: = 6 2 1 1 1 0 0 0 1 0 6 2 226 = 2 7 2 5 2 4 2 3 2 2 1 2 0 2 2 2 7 2 5 2 4 2 3 2 2 1 2 0 2 2
    • Subnetting a Class C split subnet mask # subnets # hosts/subnet total # hosts utilis. 1:7 128 2 252 126 99% 2:6 192 4 248 62 98% 3:5 224 8 240 30 94% 4:4 240 16 14 224 88% 5:3 248 32 6 192 76% 6:2 252 64 2 128 50% 7:1 254 / / / /
    • Variable Length Subnet Masks (VLSM)
      • Subnets are of different size
      • A means for conserving address space
      • How to do it:
        • how big is the biggest subnet?
        • split the class into such pieces
        • split (“sub-subnet” ) those peieces further
    • VLSM (cont.)
      • How to do VLSM
      0 255
    • VLSM and routing
      • Prerequisites:
        • routing protocol must carry subnet masks
        • or static routes must be used
    • Classfull Addressing: drawbacks
      • Classfull Addressing + Subnetting
        • at least one route per class is advertised in routing updates
      • Number of networks is doubling faster than once per year
      • Memory is not growing that fast
      • Only a few routers can keep the current number of routes
      • Route flapping
    • Classless addressing
      • Introduced by CIDR - Classless InterDomain Routing
      • Networks are grouped (aggregated) into blocks
      • Blocks of networks are advertised
      • New way of thinking:
        • there are no networks numbers, but just address space prefixes
        • there are no subnet masks, just prefix lenghts
    • Classless addresses notation
      • 10.181.215.32 /27
      • 10.181.215.32 with mask 255.255.255.224
      • binary representation of mask: 11111111.11111111.11111111.11100000
    • Classless address notation Hosts . . . 8 16 32 64 128 256 . . . 4096 8192 16384 32768 65535 . . . Prefix . . . /29 /28 /27 /26 /25 /24 . . . /20 /19 /18 /17 /16 . . . Classful . . . 1 C . . . 16 C’s 32 C’s 64 C’s 128 C’s 1 B . . . Subnet Mask . . . 255.255.255.248 255.255.255.240 255.255.255.224 255.255.255.192 255.255.255.128 255.255.255.0 . . . 255.255.240.0 255.255.224.0 255.255.192.0 255.255.128.0 255.255.0.0 . . .
    • Classless network aggregation - Supernetting Class C 24-bit prefix 11000000 192 168 64 0 10101000 01000000 Prefix Host part 00000000 Common prefix: 23 bits 11111111 11111111 1111111 0 00000000 00000000 Classless 23-bit prefix 11000000 192 168 64 /23 10101000 0100000 0 00000000 Class C next 24-bit prefix 11000000 192 168 65 0 10101000 01000001 00000000
    • Classless network aggregation (cont.)
      • Before aggregation
        • 201.222.191.0/24
        • 201.222.192.0/24
        • 201.222.193.0/24
      • After aggregation
        • 201.222.191.0/24
        • 201.222.192.0/23
    • Classless addressing and routing
      • Longest match routing
      • Route distr. between two protocols, one is not supporting classless
        • use a default route
        • “ explode” supernet info. into individual network numbers
    • Classes of routing protocols
      • The early Arpanet was completelly flat - single “network” model
        • one routing protocol, all routers had all the routing info
        • with the growth it become hard to maintaine and computationally intensive
      • Solution: split the Internet into a set of Autonomous Systems (AS)
        • Each Autonomous System is a set of routers and networks under the same administration
    • Classes of routing protocols (cont.)
      • Special routers, called “Exterior gateways” used to connect ASes
      • Two classes of routing protocols:
        • Interior routing protocols (IGP - Interior Gateway protocols)
        • Exterior routing protocols (EGP - Exterior Gateway protocols)
    • Interior Routing Protocols (IGPs)
      • Used inside an Autonomous System
      • Designed to handle more redundant links
        • Links are cheaper in a local environment => one can afford more redundant links
      • Designed with a higher bandwidth in mind
        • Cheaper bandwidth => one can use more bandwidth for the exchange of routing information
    • Interior Routing Protocols (cont.)
      • They generally contaion less ingformation than EGPs
        • IGPs in general (with exeptions) do not have to know about any other network outside the AS
      • No policy support
        • Inside AS, one generally does not want to aplly policy
        • everyone can use every available link
        • policies are generally only set on what links should be preffered
    • Interior Routing Protocols (cont.)
      • Fairly extensive metric support
        • Redudancy => one has to distinguish between redundant links
        • metrics or “costs” help in the decision proccess
      • Designed for fast convergence
        • Because of the redudancy, IGPs are designed to make quick changes if the network topology changes
    • Exterior Routing Protocols (EGPs)
      • Used to exchange routing information between ASes
      • Designed with lower bandwidth in mind
        • long distance links are more expensive => routing protocol should use less bandwidth for the exchange of routing information
      • They generally contain a lot of information
        • EGPs have to know about all external networks
        • In the Internet that might be 40.000 networks
    • Exterior Routing Protocols (cont.)
      • They assume a less reliable network
        • most of them are connection oriented for reliable delivery
      • They are designed to provide policy control
        • generally you set routing policy at the border of your routing domain
      • They do not run in every single router
        • Only at the border of your AS you have to run an EGP
        • Internal routers can be less powerfull
    • Summary
      • We have covered
        • Internet topology
        • Routing:
          • static, dynamic
          • classes of routing protocols
        • Addressing
          • classfull
            • subnetting
            • VLSM
          • classless
    • Where to get more information
      • RFC´s (RFC-1880: Internet Official Protocol Standards)
      • Books
        • D.C.Lynch, M.T.Rose: Internet System Handbook
        • D.E.Comer: Internetworking with TCP/IP
      • Mailing lists
      • Usenet News
    • Network troubleshooting
      • Ping: ICMP echo-request
      • Traceroute
        • UDP to an non-existing port
        • start with TTL=1
        • increase by 1
        • can get back:
          • ICMP time exceeded
          • ICMP port unreachable
      • TCPdump, trace utilities in routers, ...
    • Track 1: Initial configuration
      • Domain name: ceews.ceu.hu
      • PC names: tr1pcxy
        • x : row number (1 to 7)
        • y : a number of a PC inside a row (1 to 3)
      • IP address: 193.225.220.(x*8+y)
      • Network mask: 255.255.255.0
      • Default Gateway: 193.225.220.1
      • DNS: 193.225.218.100
    • Domain Name System
      • Domain Names: vislava.ceenet.waw.pl
      • IP addresses: 194.181.200.2
      • Need for automatic conversion
      • Conversion table (/etc/hosts)
      • Distributed Hierarhical Database
      • Client-Server model:
        • Server: Name Server
        • Client: Name Resolver