06. Apr. 20051INF-3190: Internet Internet Foreleser: Carsten Griwodz Email:...

06. Apr. 2005 1 INF-3190: Internet

Internet

Foreleser: Carsten GriwodzEmail: [email protected]


Data link andPhysical layer

Networklayer

Transportlayer

Applicationlayer

Internet Protocol Stackand Some Well-known Protocols

WANs

ATM

LLC & MAC

physical

LANs

MANs

IP+ ICMP+ ARP

TCP UDP

SMTP

HTTP

FTP

TELN

ET N

FS RTP


IP Routing


IP Routing Routing tables

Routers may have incomplete information Default paths

Network

10.0.0.0

Network

10.0.0.0

F

Network

20.0.0.0

Network

20.0.0.0

Network

30.0.0.0

Network

30.0.0.0

Network

40.0.0.0

Network

40.0.0.0

G H

20.0.0.5

10.0.0.5

30.0.0.6

20.0.0.6

40.0.0.7

30.0.0.7

To reach hoston network

20.0.0.0

30.0.0.0

10.0.0.0

40.0.0.0

Route to thisaddress

Deliver direct

Deliver direct

20.0.0.5

30.0.0.7

Routing table of G


IP Routing: Historical

Routers: “Core Gateways” Connect LANs to the backbone, know the routes to all

networks Exchange routing information with each other Gateway-to-Gateway Protocol (GGP):

Distance vector routing metric: physical distance

Problems Today several backbones Today not all networks are connected directly to the backbone In GGP all gateways communicate with each other

ARPANET

Local net 1 Local net 2 Local net n

G1 G2Gn

…

Originalimplementation


IP Routing: Autonomous Systems Hidden networks

Local net 2

Local net 1

Local net 3 Local net 4

G2 G3

G4

Core gateways have to be informed about hidden networks Autonomous systems (AS)

Internet domains

Boundary routers are also called Exterior gateways

Autonomous System

AS boundary router

G1

Core gateways


IP Routing: Autonomous Systems

Many autonomous systems (~70000) Have different sizes Exchange services with each other as equals or as provider/customer Have different relations to each other

Every AS has a unique number Every AS must know a route to every network

AS

ASAS

AS AS

AS

AS

AS

ASAS

ASAS

AS

ASAS

AS AS

AS

AS

AS



Stub domain One AS, several networks Networks may have different owners, but in the same AS

Multiconnected domain Like stub domain Connected to more than one other AS No through traffic

AS

ASAS

AS AS

AS

AS

AS

ASAS

ASAS

AS

ASAS

AS AS

AS

AS

AS



Peering Bi-lateral agreement between two directly connected ASes Exchange routes to all subnetworks Typically don’t offer global routes to each other

Transit domains Offer connection service to customer ASes Offer global routes to customer AS

AS

ASAS

AS AS

AS

AS

AS

ASAS

ASAS

AS

ASAS

AS AS

AS

AS

AS



Tier-1 domain Top level networks Advertise all global routes Customer to no-one No-pay agreements with their peers

Internet Exchange Point Non-profit organisation Large centers for interconnecting ASes Keeps peering costs low for smaller ASes

AS

ASAS

ASAS

ASAS

ASAS

AS

ASAS

ASAS

AS

AS

ASAS

AS

AS


IP Routing: Autonomous Systems Every AS has a unique number Every AS must know a route to

every network

AS

ASAS

ASAS

AS

AS

ASAS

AS

ASAS

ASAS

AS

AS

ASAS

AS

AS

Stub domain Multiconnected domain

Peering

Transit domains Tier-1 domains

Internet Exchange Point


IP Routing: Internal and External Routing

Direct Routing/ Interior Protocols: Both source and destination end

systems are located in the same subnetwork

source end system sends datagram to the destination end system

identification done by the local address mapping

routing is completely defined by the subnetwork routing algorithm

N0N0

N1N1

N3N3 N5N5

N4N4

N2N2

Indirect Routing/Exterior Protocols: Source and destination end system are located on different networks

source end system sends datagram to the next router each router determines the next router on the path to the destination end

system routing decision is based only on

the network and subnetwork part of the Internet address, i.e. host part not used



ASs are administrative entities Collects routing information on networks in the AS Defines boundary routers that transmit routing information to other ASs

Boundary routers will filter routes Expose information about network reachability to other ASs May transmit information about other reachable ASs (tier-1 domains,

transit domains) ISP will offer customers access to routes its sees via peerings and transits ISP will offer peers routes to customers, no routes from transits or other

peers

AutonomousSystem x

Gx

AutonomousSystem 1

G1

EGP

Place physically close to each other


Exterior Gateway Protocol Requirements,

basic conditions political economical security-related

Requirement examples to avoid certain autonomous systems to avoid certain countries to stay within one country (before going

via foreign country) data of company A should not to pass

through company B

AS

ASAS

ASAS

AS

AS

ASAS

AS

ASAS

ASAS

AS

AS

ASAS

AS

AS


Border Gateway Protocol (BGP) Previously: Internet Exterior Gateway Protocol (RFC 1654) Now: Border Gateway Protocol (RFC 1771, 1772, 1773) is de-facto

standard

BGP uses distance path mechanism Related to distance vector routing

But without count-to-infinity problem IS sends periodically a list to its neighbours containing

estimated distance and preferred Path from itself to each destination for a specified block of reachable IP addresses

Receiving IS evaluates path Distance Policy compliance

notion of a path / of how to reach other routers is distributed but, no criteria for selecting a route is distributed

Each BGP router must have its own criteria, i.e. policy

Remarks Big updates But only a limited number of routers


Interior Gateway Protocol

In general: intradomain routing individual solutions possible

Presently preferred procedures Routing Information Protocol (RIP): old, retiring Intermediate System – Intermediate System (IS-IS): long time favorite Open Shortest Path First (OSPF): scales better than IS-IS Interior Border Gateway Protocol (iBGP): combined with IS-IS and OSPF

AutonomousSystem x

IGPx

IGPx

Gx

AutonomousSystem 1

IGP1

IGP1

G1

EGP


Routing Information Protocol (RIP)

Background (regarding the originally used protocol) developed as a part of Berkeley UNIX since 1988, RIP Version 1, RFC 1058

Principle Distance Vector Routing Distance in number of hops, 15 is ∞ Periodic updates: 30 sec cycle, 180 sec with update ∞

RIP Version 2 G. Malkin, RFC 1387, 1388 and 1389 (RIP-MIB)

Uses multicast if necessary to distribute data Not broadcast

Networks without broadcast or multicast (ISDN, ATM) “Triggered" updates To be sent only if the routing table changes


Open Shortest Path First (OSPF) Background: since 1990 Internet Standard, RFCs 1247, 2178

Transition from DVR to LSR Principle

Link State Routing Several possible distance metrics Metric selection per update packet possible (RFC 1349)

Distribute updates using flooding Routing tables created using Dijkstra’s "shortest path first"

algorithm Name "Open Shortest Path First“

0248

16

Normal serviceMinimize financial cost

Maximize reliabilityMaximize throughput

Minimize delay

OSPF no. Meaning


Open Shortest Path First (OSPF) For large autonomous

systems

AS substructure AS AS backbone area Area

Router classes AS boundary routers Backbone routers Area border routers Internal routers

To other AS

To other AS


Open Shortest Path First (OSPF) Adjacency

LSR measures distance to all neighbors OSPF measures distance to all adjacent nodes

If several routers are connected by a LAN One is designated router All other routers on the LAN are adjacent only to it It is adjacent to all others

Abstraction leads to point-to-point links Required for Dijkstra’s algorithm

A F

B

C

LAN

D E G

H

Itransform to

graph A

F

B

C

D E G

H

I


Final remarks IS-IS is similar to OSPF without (working support for) areas

iBGP is often used to distribute tables for routing among ASs inside an AS

Separate the issue from dynamics of IGP

Not all routers inside an AS must carry the full external routing table

Some routers talk iBGP and have the full routing table Called route reflectors All route reflectors of an AS must be connected at all times They have route reflector clients that route all external traffic

through them

Multiconnected ASs want to save resources If two routes to a target AS exist … … and policies allow it Hot potato routing


Internet Protocol IP

Defined for the first time in 1981 J. Postel RFC 791, September 1981

Connectionless service Provide best-efforts service Without regard to whether

these machines are on the same network there are other networks in between

Packet length In theory: up to 64 kBytes In real life mostly approx. 1500 Bytes


IPv4 Datagram Format

Version IPv4: dominant version IPv6: upcoming successor to

IPv4

Protocol specific fields

VersionInternet NetworkLayers Headers

0 Not in use12345

Not in use

Not in useNot in use

Internet Protocol, version 4Stream Protocol (ST, ST-II)

6 Internet Protocol, version 67 IPv77, TP/IX, CATNIP8 PIP9 TUBA

10 Not in use1112131415

Not in useNot in useNot in useNot in useNot in use


Version IHL Type of service


D T R C

Precedence (3 bit) priority 0 (normal) ...7 (network control) influences the queuing scheme (and

not routing)

1 bit unused C (1 bit): low cost R (1 bit): high reliability T (1 bit): high throughput D (1 bit): low delay

OLD definition Was ignored by routers Redefined by DiffServ


Version IHL DS


0

Class selector codepoints If of the form xxx000

DS Field Differentiated

Services Field New definition

NEW definition DiffServ compliant Not widely deployed

yet

0

Differentiated Services Codepoint xxxxx0 reserved for standardization xxxx11 reserved for local use xxxx01 open for local use, may be

standardized later


Version IHL DS


IdentificationTotal length

DM Fragment offsetTime to live Protocol

Destination AddressSource address

Header checksum

Protocol type of higher level protocol for transmission

1 – ICMP Internet Control Message Protocol 2 – IGMP Internet Group Management Protocol 3 – GGP Gateway to Gateway Protocol 4 – IP IP in IP tunneling 5 – ST ST–II in IP tunneling 6 – TCP TCP …


IPv4 Segmentation/Reassembly

Transparent segmentation

Non-transparent segmentation Used in the Internet

IP routers


IPv4 Segmentation/Reassembly Total length

Length of the unsegmented datagram in bytes ≥576 bytes

≤65535 bytes Identification

Unique for all segments of a datagram with same src/dst pair Flags

DF (1 bit): don’t fragment MF (1 bit): more fragments

Fragment offset Offset of this fragment in the datagram in multiples of 8 bytes


Options (0 or more)

Destination AddressSource address

Time to live Protocol Header checksumIdentification DM Fragment offset

Version IHL Total length


Data

Padding

DS


IP Version 6 Objectives To support billions of end systems

longer addresses To reduce routing tables To simplify protocol processing

simplified header

To increase security security means integrated

To support real-time data traffic flow label, traffic class

To provide multicasting To support mobility (roaming)

To be open for change (future) extension headers

To coexist with existing protocols

Scalability

Addressing IPv4limitations

Coexistance


IPv6 vs. IPv4

VersionPriority Flow labelPayload length Next header Hop Limit

Destination Address(128 bit)

Source address(128 bit)

Options (0 or more)

Destination Address (32 bit)Source address (32 bit)

Time to live Protocol Header checksumIdentification DM Fragment offset

Version IHL Type of service Total lengthPRE ToSIPv4 Header

IPv6 Header


IPv6 Header Fields

VersionPriority Flow labelPayload length Next header Hop Limit

Destination Address

Source address

IPv6 Header

01234567

89

101112131415

Not characterizedFillerUnattendedReservedAttended bulk transferReservedInteractiveInternet management

Continuous rate traffic

With flow control Without flow control

Priority differentiation of

sources lower number < lower

priority


Internet Control Message Protocol (ICMP)

History J. Postel RFC 792, Sept. 1981

Purpose to communicate network layer information

mostly error reportinge.g. in ftp, telnet, http appears "destination network unreachable"

ICMP origin, e.g.: a router was unable to find the given destination address router sent back ICMP (Type 3) packet sending host received the packet, returned error code to TCP TCP returned error code to application (e.g. ftp, telnet, http)

between hosts, routers (and gateways)

ICMP messages are sent as IP packets i. e. the first 32 bits of the IP data field are ICMP headers


Internet Control Message Protocol (ICMP)

Header structure

Type 16 types, a. o.

destination or port or protocol unreachable fragmentation necessary but DF (don’t fragment) DF is set source route failed, redirect (for routing) echo-request and echo-reply (e.g. for "ping" program) source quench (packet for congestion control)

Code states cause if type is "destination unreachable"

e. g. net, host, protocol, port unreachable or fragmentation needed, source route failed

Type Code Checksum


IPv4 Addresses andInternet Subnetworks

Original global addressing concept for the Internet For addressing end systems and intermediate systems each network interface (not end system) has its own unique address 5 classes

0 Network Host

1

7

0

1 1 0

Network Host

Network Host

1 1 01 Multicast address

1 111 Reserved

24

14 16

21 8

28

28

A

B

C


IPv4 Address andInternet Subnetworks

Networks grow and should be somehow structured several networks instead of one preferable but getting several address areas is hard

since address space is limited e.g., university may have started with class B address, doesn’t get

second one Problem

class A, B, C refer to one network, not collection of LANs

Allow a network to be split into several parts for internal use still look like single network to outside world


IPv4 Address andInternet Subnetworks

Idea local decision for subdividing host share

into subnetwork portion and end system portion

1 0 Network Host14 16

Use “subnet mask” to distinguish network and subnet part from host part

Routing with 3 levels of hierarchy Algorithm in router

(by masking bits: AND between address and subnet mask): packet to another network (yes, then to this router) packet to local end system (yes, then deliver packet) packet to other subnetwork (yes, then reroute to appropriate router)

Subnet Host6 10

1 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 1 1 1 0 0 0 0 0 0 1 0e.g. address

129.8.7.2:

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0Subnet mask:

To write down subnet addresswith subnet mask use either 129.8.4.0/255.255.252.0or 129.8.4.0/221 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0Subnet address:

& &


CIDR: Classless InterDomain Routing

Subnetting not good enough Too many organizations require addresses

in principle many addresses due to 32-bit address space but inefficient allocation due to class-based organization

class A network with 16 million addresses too big for most cases class C network with 256 addresses is too small most organizations are interested in class B network, but there are only

16384 (in reality, class B too large for many organizations) Large number of networks leads to large routing tables

Introduction of CIDR (Classless InterDomain Routing) (RFC1519)

CIDR Principle to allocate IP addresses in variable-sized blocks

(without regard to classes) e.g., request for 2000 addresses would lead to

assignment of 2048 address block starting on 2048 byte boundary but, dropping classes makes forwarding more complicated


CIDR: Classless InterDomain Routing

Search for longest matching prefix if several entries with different subnet mask length may match

then use the one with the longest mask i.e., AND operation for address & mask must be done for each

table entry

Entries may be aggregated to reduce routing tables

Router194.24.0.0/19

Router

Router

Unassigned 194.24.12.0/22

Router

194.24.0.0/21

194.24.8.0/22

194.24.16.0/20


IPv6 Addresses

0000 00010000 0010000 0100000 0110000 1000100101001110010111011101111 01111 101111 1101111 1110 01111 1110 101111 1110 111111 1111

UnassignedOSI NSAP address

Novell Netware IPX addressesUnassignedUnassignedUnassignedUnassigned

Provider-based addressesUnassigned

Geographic-based addressesUnassignedUnassignedUnassignedUnassignedUnassignedUnassignedUnassigned

Link local use addressesSite local use address

Multicast

0000 0000 Reserved (including IPv4) 1/256

1/128

1/321/161/8

1/16

1/64

1/512

1/1024

1/256

1/256

1/1281/128

1/128

1/32

1/1024

1/81/81/81/81/8

Prefix (binary) Usage Fraction


IPv6 Addresses and Anycast Provider based: approx. 16 mio. companies allocate addresses Geographically based: allocation as it is today Link, site-used: address has only local importance (security,

Firewall concept) Should make NAT (network address translation) useless

Anycast definition previously

unicast, broadcast and multicast now (new)

anycast send data to one member of a group

for example to the member which is the nearest one geographically i.e. a system within a pre-defined group is to be accessed

Anycast application To search for the nearest web-server To locate the nearest router of a multicast group

in order to participate in group communication

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06. Apr. 20051INF-3190: Internet Internet Foreleser: Carsten Griwodz Email:...

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