1 addressing. 2 outline network addressing network packet format and forwarding nat, dhcp, ipv6

1

Addressing

2

Outline

Network addressing Network packet format and forwarding NAT, DHCP, IPv6

3

IP Addressing: introduction

IP address: 32-bit identifier for host, router interface

interface: connection between host/router and physical link router’s typically have

multiple interfaces host may have multiple

interfaces IP addresses associated

with each interface

223.1.1.1

223.1.1.2

223.1.1.3

223.1.1.4 223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.2223.1.3.1

223.1.3.27

223.1.1.1 = 11011111 00000001 00000001 00000001

223 1 11

4

IP Addressing

IP address: network part (high

order bits) host part (low order

bits) What’s a network ? (from

IP address perspective) device interfaces with

same network part of IP address

can physically reach each other without intervening router

223.1.1.1

223.1.1.2

223.1.1.3

223.1.1.4 223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.2223.1.3.1

223.1.3.27

network consisting of 3 IP networks(for IP addresses starting with 223, first 24 bits are network address)

LAN

5

IP Addressing

How to find the networks? Detach each interface

from router, host create “islands of

isolated networks

223.1.1.1

223.1.1.3

223.1.1.4

223.1.2.2223.1.2.1

223.1.2.6

223.1.3.2223.1.3.1

223.1.3.27

223.1.1.2

223.1.7.0

223.1.7.1223.1.8.0223.1.8.1

223.1.9.1

223.1.9.2

Interconnected system consisting

of six networks

How many isolated networks?

6

IP address classes

Network ID Host ID

8 16

Class A32

0

Class B 10

Class C 110

Multicast AddressesClass D 1110

Reserved for experimentsClass E 1111

24

Network ID

Network ID

Host ID

Host ID

1.0.0.0 to 127.255.255.255

128.0.0.0 to 191.255.255.255

192.0.0.0 to 223.255.255.255

224.0.0.0 to 239.255.255.255

7

Special IP Addresses

127.*.*.*: local host (a.k.a. the loopback address) Private addresses

http://www.rfc-editor.org/rfc/rfc1918.txt Class A: 10.0.0.0 - 10.255.255.255 (10/8 prefix) Class B: 172.16.0.0 - 172.31.255.255 (172.16/12 prefix) Class C: 192.168.0.0 - 192.168.255.255 (192.168/16 prefix)

255.255.255.255 IP broadcast to local hardware that must not be forwarded http://www.rfc-editor.org/rfc/rfc919.txt Same as network broadcast if no subnetting

IP of network broadcast=NetworkID+(all 1’s for HostID) 0.0.0.0

IP address of unassigned host (BOOTP, ARP, DHCP) Default route advertisement

8

IP Addressing Problem #1 (1984)

Subnet addressing http://www.rfc-editor.org/rfc/rfc917.txt Address problem of inefficient use of address space For class B & C networks

Class A (rarely given out, not many of them given out by IANA) Class B = 64k hosts

o Very few LANs have close to 64K hostso Electrical/LAN limitations, performance or administrative reasons o e.g., class B net allocated enough addresses for 64K hosts, even if only 2K hosts in

that network Class C = 256 hosts

Need simple way to get multiple “networks” Use bridging, multiple IP networks or split up single network

address ranges (subnet) Reduce the total number of addresses that are assigned, but

not used

9

Subnetting

Variable length subnet masks Subnet a class B address space into several chunks

Network Host

Network HostSubnet

1111.. 00000000..1111 Mask

10

Subnetting Example

Assume an organization was assigned address 150.100

Assume < 100 hosts per subnet How many host bits do we need?

Seven

What is the network mask? 11111111 11111111 11111111 10000000 255.255.255.128

11

IP Address Problem #2 (1991)

Address space depletion In danger of running out of classes A and B Class A

Very few in number IANA frugal in giving them out

Class B Subnetting only applied to new allocations sparsely populated people refuse to give it back

Class C too small for most domains APNIC has only class C addresses

12

Some Solution

Solution Assign multiple consecutive class C address blocks Supernetting

http://www.rfc-editor.org/rfc/rfc1338.txt Later known as Classless Inter-Domain Routing

(CIDR) http://www.rfc-editor.org/rfc/rfc1518.txt http://www.rfc-editor.org/rfc/rfc1519.txt

13

IP addressing: CIDR

Classful addressing: inefficient use of address space, address space exhaustion e.g., class B net allocated enough addresses for 65K

hosts, even if only 2K hosts in that network

CIDR: Classless InterDomain Routing network portion of address of arbitrary length address format: a.b.c.d/x, where x is # bits in network

portion of address

11001000 00010111 00010000 00000000

networkpart

hostpart

200.23.16.0/23

14

IP addresses: how to get one?

Q: How does host get IP address?

hard-coded by system admin in a file Windows: control-panel->network->configuration->tcp/ip-

>properties UNIX: /etc/rc.config Linux (Redhat): /etc/sysconfig/network-script/ifcfg-eth

DHCP: Dynamic Host Configuration Protocol: dynamically get address from as server “plug-and-play”

(more shortly)

15

IP addresses: how to get one?

Q: How does network get network part of IP addr?A: gets allocated portion of its provider ISP’s

address space

ISP's block 11001000 00010111 00010000 00000000 200.23.16.0/20

Organization 0 11001000 00010111 00010000 00000000 200.23.16.0/23 Organization 1 11001000 00010111 00010010 00000000 200.23.18.0/23 Organization 2 11001000 00010111 00010100 00000000 200.23.20.0/23 ... ….. …. ….

Organization 7 11001000 00010111 00011110 00000000 200.23.30.0/23

16

Hierarchical addressing: route aggregation

“Send me anythingwith addresses beginning 200.23.16.0/20”

200.23.16.0/23

200.23.18.0/23

200.23.30.0/23

Fly-By-Night-ISP

Organization 0

Organization 7Internet

Organization 1

ISPs-R-Us“Send me anythingwith addresses beginning 199.31.0.0/16”

200.23.20.0/23Organization 2

...

...

Hierarchical addressing allows efficient advertisement of routing information:

17

Hierarchical addressing: more specific routes

ISPs-R-Us has a more specific route to Organization 1

“Send me anythingwith addresses beginning 200.23.16.0/20”

200.23.16.0/23

200.23.18.0/23

200.23.30.0/23

Fly-By-Night-ISP

Organization 0

Organization 7Internet

Organization 1

ISPs-R-Us“Send me anythingwith addresses beginning 199.31.0.0/16or 200.23.18.0/23”

200.23.20.0/23Organization 2

...

...

18

Where to obtain IP address

Q: How does an ISP get block of addresses?A: ICANN: Internet Corporation for Assigned

Names and Numbers allocates addresses manages DNS assigns domain names, resolves disputes

19

Outline

Overview of Network Layer Network addressing Network packet format and forwarding NAT, DHCP, IPv6

20

Getting a datagram from source to dest.

IP datagram:

223.1.1.1

223.1.1.2

223.1.1.3

223.1.1.4 223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.2223.1.3.1

223.1.3.27

A

BE

miscfields

sourceIP addr

destIP addr data

datagram remains unchanged, as it travels source to destination

addr fields of interest here

Dest. Net. next router Nhops

223.1.1 1223.1.2 223.1.1.4 2223.1.3 223.1.1.4 2

forwarding table in A

21


Starting at A, send IP datagram addressed to B:

look up net. address of B in forwarding table

find B is on same net. as A link layer will send datagram

directly to B inside link-layer frame B and A are directly

connected


223.1.1 1223.1.2 223.1.1.4 2223.1.3 223.1.1.4 2

miscfields223.1.1.1223.1.1.3data

223.1.1.1

223.1.1.2

223.1.1.3

223.1.1.4 223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.2223.1.3.1

223.1.3.27

A

BE


22



223.1.1 1223.1.2 223.1.1.4 2223.1.3 223.1.1.4 2

Starting at A, dest. E: look up network address of E

in forwarding table E on different network

A, E not directly attached routing table: next hop router

to E is 223.1.1.4 link layer sends datagram to

router 223.1.1.4 inside link-layer frame

datagram arrives at 223.1.1.4 continued…..

miscfields223.1.1.1223.1.2.3 data

223.1.1.1

223.1.1.2

223.1.1.3

223.1.1.4 223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.2223.1.3.1

223.1.3.27

A

BE


23


Arriving at 223.1.4, destined for 223.1.2.2

look up network address of E in router’s forwarding table

E on same network as router’s interface 223.1.2.9 router, E directly attached

link layer sends datagram to 223.1.2.2 inside link-layer frame via interface 223.1.2.9

datagram arrives at 223.1.2.2!!! (hooray!)

miscfields223.1.1.1223.1.2.3 data Dest. Net router Nhops interface

223.1.1 - 1 223.1.1.4 223.1.2 - 1 223.1.2.9

223.1.3 - 1 223.1.3.27

223.1.1.1

223.1.1.2

223.1.1.3

223.1.1.4 223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.2223.1.3.1

223.1.3.27

A

BE

forwarding table in router

24

IP datagram format

ver length

32 bits

data (variable length,typically a TCP

or UDP segment)

16-bit identifier

header checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentation/reassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

head.len

type ofservice

“type” of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) E.g. timestamp,record routetaken, specifylist of routers to visit.

how much overhead with TCP?

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

25

IP Fragmentation & Reassembly

network links have MTU (max.transfer size) - largest possible link-level frame. different link types,

different MTUs large IP datagram divided

(“fragmented”) within net one datagram becomes

several datagrams “reassembled” only at final

destination IP header bits used to

identify, order related fragments

fragmentation: in: one large datagramout: 3 smaller datagrams

reassembly

26

IP Fragmentation and Reassembly

ID=x

offset=0

fragflag=0

length=4000

ID=x

offset=0

fragflag=1

length=1500

ID=x

offset=1480

fragflag=1

length=1500

ID=x

offset=2960

fragflag=0

length=1040

One large datagram becomesseveral smaller datagrams

Example 4000 byte

datagram MTU = 1500 bytes

27

Fragmentation is Harmful

Uses resources poorly Forwarding costs per packet Best if we can send large chunks of data Worst case: packet just bigger than MTU

Poor end-to-end performance Loss of a fragment

Reassembly is hard Buffering constraints

28

Avoid fragmentation

Path MTU Discovery in IP http://www.rfc-editor.org/rfc/rfc1191.txt Hosts dynamically discover minimum MTU of path Algorithm:

Initialize MTU to MTU for first hop Send datagrams with Don’t Fragment bit set If ICMP “pkt too big” msg, decrease MTU

What happens if path changes? Periodically (>5mins, or >1min after previous increase),

increase MTU Some routers will return proper MTU MTU values cached in routing table

29

ICMP: Internet Control Message Protocol

used by hosts, routers, gateways to communication network-level information error reporting:

unreachable host, network, port, protocol

echo request/reply (used by ping)

network-layer “above” IP: ICMP msgs carried in IP

datagrams ICMP message: type, code plus

first 8 bytes of IP datagram causing error

Type Code description0 0 echo reply (ping)3 0 dest. network unreachable3 1 dest host unreachable3 2 dest protocol unreachable3 3 dest port unreachable3 6 dest network unknown3 7 dest host unknown4 0 source quench (congestion control - not used)8 0 echo request (ping)9 0 route advertisement10 0 router discovery11 0 TTL expired12 0 bad IP header

30

Traceroute

Based on ICMP: provides delay measurement from source to router along end-end Internet path towards destination. sends three packets that will reach router i on path

towards destination Set the TTL incrementally from 1 up to 30 router i will return ICMP warning (type 11) back. sender times interval between transmission and reply.

TTL=1

TTL=2

TTL=3

31

Outline

Network addressing Network packet format and forwarding NAT, DHCP, IPv6

32

NAT: Network Address Translation

10.0.0.1

10.0.0.2

10.0.0.3

10.0.0.4

138.76.29.7

local network(e.g., home network)

10.0.0/24

rest ofInternet

Datagrams with source or destination in this networkhave 10.0.0/24 address for

source, destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address: 138.76.29.7,different source port numbers

33


Motivation: local network uses just one IP address as far as outside word is concerned: no need to be allocated range of addresses from ISP:

- just one IP address is used for all devices can change addresses of devices in local network

without notifying outside world can change ISP without changing addresses of

devices in local network devices inside local net not explicitly addressable,

visible by outside world (a security plus).

34


ImplementationA NAT router must:

outgoing datagrams: replace (source IP address, port #) of every outgoing datagram to (NAT IP address, new port #)

. . . remote clients/servers will respond using (NAT IP address, new port #) as destination addr.

remember (in NAT translation table) every (source IP address, port #) to (NAT IP address, new port #) translation pair

incoming datagrams: replace (NAT IP address, new port #) in dest fields of every incoming datagram with corresponding (source IP address, port #) stored in NAT table

35


10.0.0.1

10.0.0.2

10.0.0.3

S: 10.0.0.1, 3345D: 128.119.40.186, 80

1

10.0.0.4

138.76.29.7

1: host 10.0.0.1 sends datagram to 128.119.40, 80

NAT translation tableWAN side addr LAN side addr

138.76.29.7, 5001 10.0.0.1, 3345…… ……

S: 128.119.40.186, 80 D: 10.0.0.1, 3345

4

S: 138.76.29.7, 5001D: 128.119.40.186, 80

2

2: NAT routerchanges datagramsource addr from10.0.0.1, 3345 to138.76.29.7, 5001,updates table

S: 128.119.40.186, 80 D: 138.76.29.7, 5001

3

3: Reply arrives dest. address: 138.76.29.7, 5001

4: NAT routerchanges datagramdest addr from138.76.29.7, 5001 to 10.0.0.1, 3345

36

DHCP: Dynamic Host Configuration Protocol

Goal: allow host to dynamically obtain its IP address from network server when it joins networkCan renew its lease on address in useAllows reuse of addresses (only hold address while connected an

“on”Support for mobile users who want to join network (more shortly)

DHCP overview: host broadcasts “DHCP discover” msg DHCP server responds with “DHCP offer” msg host requests IP address: “DHCP request” msg DHCP server sends address: “DHCP ack” msg

37

DHCP client-server scenario

223.1.1.1

223.1.1.2

223.1.1.3

223.1.1.4 223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.2223.1.3.1

223.1.3.27

A

BE

DHCP server

arriving DHCP client needsaddress in thisnetwork

38

DHCP client-server scenario

DHCP server: 223.1.2.5 arriving client

time

DHCP discover

src : 0.0.0.0, 68 dest.: 255.255.255.255,67yiaddr: 0.0.0.0transaction ID: 654

DHCP offer

src: 223.1.2.5, 67 dest: 255.255.255.255, 68yiaddrr: 223.1.2.4transaction ID: 654Lifetime: 3600 secs

DHCP request

src: 0.0.0.0, 68 dest:: 255.255.255.255, 67yiaddrr: 223.1.2.4transaction ID: 655Lifetime: 3600 secs

DHCP ACK

src: 223.1.2.5, 67 dest: 255.255.255.255, 68yiaddrr: 223.1.2.4transaction ID: 655Lifetime: 3600 secs

39

IPv6

Initial motivation: 32-bit address space completely allocated by 2008.

Additional motivation: header format helps speed processing/forwarding header changes to facilitate QoS new “anycast” address: route to “best” of several

replicated servers

IPv6 datagram format: fixed-length 40 byte header no fragmentation allowed

40

IPv6 Header (Cont)

Priority: identify priority among datagrams in flowFlow Label: identify datagrams in same “flow.” (concept of“flow” not well defined).Next header: identify upper layer protocol for data

41

ver total length

data (variable length,typically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

head.len

type ofservice

flgsfragment

offsetprotocol

32 bit destination IP address

Options (if any)

IPv4 vs. IPv6

42

Differences Between Ipv4 and IPv6

Address length: 32 vs. 128 Fragmentation: IPv6 has no fragmentation Type of service (TOS): IPv6 has no TOS Checksum: removed entirely to reduce

processing time at each hop Options: allowed, but outside of header,

indicated by “Next Header” field; options specify how to deal with the packet if a header is unknown

ICMPv6: new version of ICMP additional message types, e.g. “Packet Too Big” multicast group management functions

43

Transition From IPv4 To IPv6

Not all routers can be upgraded simultaneous no “flag days” How will the network operate with mixed IPv4 and IPv6

routers?

Two proposed approaches: Dual Stack: some routers with dual stack (v6, v4) can

“translate” between formats Tunneling: IPv6 carried as payload in IPv4 datagram

among IPv4 routers

44

Dual Stack Approach

A B E F

IPv6 IPv6 IPv6 IPv6

C D

IPv4 IPv4

Flow: XSrc: ADest: F

data

Flow: ??Src: ADest: F

data

Src:ADest: F

data

A-to-B:IPv6

Src:ADest: F

data

B-to-C:IPv4

B-to-C:IPv4

B-to-C:IPv6

45

Tunneling

A B E F

IPv6 IPv6 IPv6 IPv6

tunnelLogical view:

Physical view:A B E F

IPv6 IPv6 IPv6 IPv6

C D

IPv4 IPv4


data


data


data

Src:BDest: E


data

Src:BDest: E

A-to-B:IPv6

E-to-F:IPv6

B-to-C:IPv6 inside

IPv4

B-to-C:IPv6 inside

IPv4

46

Backup Slides

47

IP quality of service

IP originally had “type-of-service” (TOS) field to eventually support quality Not used, ignored by most routers

Then came int-serv (integrated services) and RSVP signalling Per-flow quality of service through end-to-end

support Setup and match flows on connection ID Per-flow signaling Per-flow network resource allocation (*FQ, *RR

scheduling algorithms)

48


RSVP http://www.rfc-editor.org/rfc/rfc2205.txt Provides end-to-end signaling to network elements General purpose protocol for signaling information Not used now on a per-flow basis to support int-serv,

but being reused for diff-serv. int-serv

Defines service model (guaranteed, controlled-load) Dozens of scheduling algorithms to support these

services WFQ, W2FQ, STFQ, Virtual Clock, DRR, etc. If this class was being given 5 years ago….

49


Why did RSVP, int-serv fail? Complexity

Scheduling Routing Per-flow signaling overhead

Lack of scalability Per-flow state Route pinning

Economics Providers with no incentive to deploy SLA, end-to-end billing issues

QoS a weak-link property Requires every device on an end-to-end basis to

support flow

50


Now it’s diff-serv… Use the “type-of-service” bits as a priority marking Core network relatively stateless AF

Assured forwarding (drop precedence) EF

Expedited forwarding (strict priority handling)

51

IPv6 Addressing (standardized in 1995)

Length: 128 bits (RFC 1752)

010 Registry Provider ID Subscriber ID Subnet ID Interface IDProvider-based unicastn m o p q

1111111010 0 Interface ID Link-local use unicastn 118-n

1111111011 0 Site-local use unicastn

Subnet ID Interface IDm 118-n-m

0000………………………..…...0000 Embedded IPv4 unicast 0000 IPv4 address 32

11111111 Flags Multicast4

Group ID 112

80 16

0000………………………..…...0000 FFFF IPv4 address 3280 16

Scope

3

10

10

48

Anycast

1 addressing. 2 outline network addressing network packet format and forwarding nat, dhcp, ipv6

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