G. Bianchi, G. Neglia

Transcription

1

2 R Net R3 R2 Routing Table dest Next Hop /16 Direct fwd / / / / !"! ! " # $ $ % & ' & ( &

3 #$$$%& "! "! #! $ %& %' () * % +, %& % - ( Router Ethernet FDDI Host Sub-Net ATM! % & ) * )!., % / 0 1 +, * # - ) x x.0! " " #$ #% &! ' ( # )! "

4 NET ID (14bit) HOST ID (16 bit) NET ID (14bit) SUBNET ID (n bit) HOST ID (16-n bit) ' ( () "!# $%&&%&' ( ) ) *$$&*$$&& +, ) * "+ *!,! "-! &&& &&& - $. ". /0 &&& /prefix-length notation ". &&1&2 (dot decimal notation) 03&022&2&2. 4 &&& 03&022&1&2. " 45 4, (! 03&022&1&2/0

5 *% +,-.) network address = natural mask = $,/0.) 1 0 NET ID (14bit) SUBNET ID (8 bit) HOST ID (8 bit) ) * * () * * () * * (. # * /6 0, , % '!! 2 $ / ( ( ( (0 (0 (. 3) NET ID (21bit) HOST ID (8 bit) NET ID (21bit) Subnet (3 bit) ( ( ( / ( ( ( /2 5 ) ( ( ( / ( ( ( / ( ( ( /2 5 * ( ( ( / ( ( ( / ( ( ( /2 8 6 & Host id (5bit)

6 6 )& = = = = = = = = / / !! : 0 -, network host ) -, - / ; / / 0 - & network subnet host /29 4

7 /.8 & ) default $ # Net = subnet mask = $ 9 : 9 ; < + = = > Routing Table Subnet mask: dest Next Hop Direct fwd Direct fwd default Net = ; subnet mask May be quite a complex Routing table VLSM will help (later) To other nets To To other subnets

8 3 9: algebra 12 hosts Math dept 22 hosts B Link-1 A physics 10 host Computation 28 host Link-2 C 3 9: Math dept /2 up to 30 hosts (9-126) B algebra /2 up to 30 hosts (33-62) Link-1 A physics /2 up to 30 hosts ( ) Computation /2 up to 30 hosts (65-94) Link-2 C

9 3 92: Math dept /2 up to 29 hosts (9-126) algebra /2 up to 29 hosts (33-62) Link /2 B Subnet mask: / SUBNETS: Math /2 Link /2 Algebra /2 Physics /2 Comput /2 Link /2 Link / / /2 C A physics /2 up to 28 hosts ( ) Computation /2 up to 29 hosts (65-94) ;( ;$( ) 1< 494=>:

10 ;$( ). $ )$.) + == A Subnets may significantly vary in relative size (computer room = 200 hosts, secretary = 4 hosts ) consider a 4 host network with mask : wastes 250 IP addresses! /! % = $% ( ( A '% pc-net 100 host A x-net-1 20 host B Link-1 Link-3 ws-net 20 host Link-2 x-net-2 10 host < < < = &! > " # * $ < 4&6 0 6 )? 3= ( & - 11 C

11 .$;( /2 pc-net /25 (0-12, 126 host) B /2 Link-1 A Link /2 x-net /2 (0-31, 30 host) ws-net /25 ( , 126 host) Link /2 C x-net /2 (32-63, 30 host) mask mask ) (0 6 B (0 (. 3) 4 ) * ) (0 6 B (0 (. 3) * 0 ) 6 (pc-net) 0 1 ) (0 6 B (0 (0 ) B 3) * 0 ) 6?;( / 6 ( " 8) 9 ( ) (0 6 B (0 (0 ) B 3) (: 2. (ws-net) 0 1 ) (0 6 B (0 (0 6. 3) 2. (x1-net) 0 1 ) (0 6 B (0 (0 1 ) 3) ) (0 6 B (0 (0 1 ) 3) B ) (0 6 B (0 (). B 3) B 0 1 ) (0 6 B (0 () ) 4 3) (available) (x2-net) 0 1 ) (0 6 B (0 (). B ) (0 6 B (0 () 0 ) ) (0 6 B (0 () ) (0 6 B (0 () ) , 4

12 <.$;( $ pc-net /25 (0-12, 126 host) /30 Link-1 B Point2point links: A Link /30 x-net /2 ( , 30 host) ws-net /2 ( , 30 host) Link / C x-net /28 (192-20, 14 host) " " " #, ! A $

13 ;( 9: '! " "! '! " ( net mask route * 0 -, 2 A 0 0 & ; ! "!# $ "! $ % & ' (!!$ 1& pc-net /25 (0-12, 126 host) ws-net /2 ( , 30 host) /30 Link-1 B Point2point links: Link / Link /30 Router C table / / / /28 Direct fwd /28 Direct fwd G. Bianchi, G Neglia /30 Direct fwd /30 Direct fwd C A x-net /2 ( , 30 host) x-net /28 (192-20, 14 host)

14 ;( 0 1+, ;,!! << -! Substantial reduction of routing table sizes Multiple route aggregation ;( 0 1+, ;,!! << -! Substantial reduction of routing table sizes Multiple route aggregation

15 ! " #$%&%'%'()# *! " + *",- * ". - Router R Edificio A hosts Edificio B hosts Edificio D 11 hosts Edificio C 10 55hosts Edificio E 12 hosts / / / / / / Router R / Edificio B 55 hosts È sufficiente uno /24, es: /24 Una soluzione possibile, con massima aggregazione dei route, è illustrata in figura (si assume che il routing esterno alla rete avvenga tramite l interfaccia remota ) Edificio A 110 hosts /25 Edificio C 10 hosts Edificio D 11 hosts / /28 Edificio E 12 hosts /28

16 / / / / È sufficiente uno /24, es: /24 Una soluzione possibile, con massima aggregazione dei route, è illustrata in figura (si assume che il routing esterno alla rete avvenga tramite l interfaccia remota ) Router R / Edificio B 55 hosts Edificio A 110 hosts /25 Edificio C 10 hosts Edificio D 11 hosts / /28 Edificio E 12 hosts /28 / /! " #$%&%'%'()# *" + *",- * ". - Router R Edificio A 10 hosts Edificio B 110 hosts Edificio D 11 hosts Edificio C 55 hosts Edificio E 12 hosts

17 / / / / / / Router R / Edificio B 110 hosts È sufficiente uno /24, es: /24 Una soluzione possibile, con massima aggregazione dei route, è illustrata in figura (si assume che il routing esterno alla rete avvenga tramite l interfaccia remota ) Edificio A 10 hosts /28 Edificio C 55 hosts Edificio D 11 hosts /28 no simple aggregation! /26 Edificio E 12 hosts /28 1@ ;( 9/: A( $B<.'$ )+? & ( " = % 3 4

18 ! / / / / È sufficiente uno /24, es: /24 Una soluzione possibile, con massima aggregazione dei route, è illustrata in figura (si assume che Il routing esterno alla rete avvenga tramite l interfaccia remota ): Router R / Edificio B 110 hosts Edificio A 10 hosts /28 Edificio C 55 hosts Edificio D 11 hosts / /26 Edificio E 12 hosts /28 3 ;( B " $ C 0 6 #

19 1.$;( ) 8 0 # 8 0 % 8 0! 8 0! #C1 #!C 1 1<>/ 9445:

20 '$& R Net R3 R2 Routing Table dest Next Hop Direct fwd *$44/# ( In early years, Class B addresses given away! Inefficient division into A, B, C classes byte-word: unwise choice (class C too little, class B too big) The aftermath: much better, e.g. C=10 bits, B=14 bits Projections at the time: class B exhaustion by 1994/95 $ % < : ==

21 *$ $0 $%.)9 : $ C D! ) * 4 ( A%B0#6.) D $%$ 1.$ 2 ) R2 Net R2 Routing Table dest R3 Next Hop /xx Direct fwd / / / /

22 *$44/# - Multiple class C allocation dramatic for routing tables necessary because of Class B exhaustion entries highly critical for performance» 2M class C: WAY OUT of the capabilities of routing sw & hw Projections at the time End 1990: 2190 routes; end 1992: 8500 routes; End 1995 projection: 0000 routes (critical); End 1995 factual: routes thanks to classless routing Mid 1999: routes Net ( R1 Net Net R R3 ) * R2 Routing Table Destination Network Next Hop Direct forward Direct forward Default routes: suboptimal traffic balancing Core routers: cannot have default routes (large tables) HW and SW limits on routing table lookup time Routing table updates are critical (large tables traveling among routers for updates)

23 #!C 1 #C1 3 %% 4 '6% 00> !5 ) + 6! 32 bits: unwise choice nobody could expect such an Internet growth and Internet appliances will have a terrific impact unwise address assignment in early days class B addresses with less than 100 hosts are common!! Projections (RFC 152): address depletion between 2005 and 2011 Ultimate solution: IPv6 (128 bits address!) #C1 = + %/.) = > C! =C "! % = " =C ( (/ E A 4 ##C1+;( $ D"3#22

24 #C / / / , $!!"! -!!!.!! * + " " / 0 / ) & $ )*. " 5 * 5 ( A : 8 D / 0 0 6! - - #C1+ : E -! - -! - - &0 6 F - = F 1 #!/ "! * + $! * * 0! 3$ 0 4 &

25 ' 0!.) ) ) * * () * * () * ) (. /5/4-,// 1.$#C Net R1 Net Net R R Dest.Net R2 Routing Table Dest.Netmask Next Hop Direct forward Direct forward Corporate Supernet address: / ) * +

26 .)% Organization assigned 2 n class C addresses may arbitrarily deploy subnetworks with more than 254 hosts! This was impossible with class C, as natural netmask was /24 BUT Software running on all the subnet hosts need to accept larger masks than natural one e.g. setting netmask = for host IP address may be forbidden by sw 1@ #C1 8?*8 Routing protocol must carry network prefix information with each route advertising all routers must implement a consistent forwarding algorithm based on the longest match for route aggregation to occur, addresses must be assigned to be topologically significant

27 1.$ $! ( / ( ) " )$ +! #! %!!!? #C1! C : * #! $ 0 # + 8 : : )# * #, - #! 6 / % 6 - G 8 - &H I # & 4

28 $. )+? & ( % 3 4 R1: R2: R3: " 38 4= 5 *! $ " ( A $, D0 1 * (. (). () ( ( ( * J 8 ( / ( ) ( ( (. + # 8 )$ 8 ( 5 8 " $ / ( ( (. ' 0, 0 0 " E K 0 "

29 )$ + 3# 6 4 ( ) : E # )$ At a point in time, organization A selects Eunet as new ISP! / = D! = " = C? - and even think to organizations that re-sells subnets... )$ + 3# 6 4 ( ) : E # )$ Then organization A keeps the same address block Eunet is in charge to advertise the new block, too, by injecting in the internet more specific route infos This has created a new entry in routing tables, to be solved with longest match

30 *$ #C1 & + (!5 $ %#@' $! AB " % C *& < Address ownership (portable blocks): dramatic» Proposals (not accepted) to allows ownership only up to /9 ISPs» Current rule : ownership starts from 8192 host networks (/19) Address lending» Renumbering necessary when changing ISP 4&+!# D #E '6% 030> unlikely, as they are viewed as assets!! ')&# 91<4=: IANA-Allocated Allocated,, Non-Internet Routable, IP Address Schemes Class Network Address Range A B C ( 6 0-6, E - ) * - )# * # ) * )! - * # - - ( 2, - -

31 .)'* Inside Network Outside Network NAT Internet Source Address Inside Local IP Address NAT Table Inside Global IP Address (.$# 9 % : #6&- 9#6! #6: *$ 0 ) B " " A " 4 although mostly designed to be as close as possible to IPv4 6% A? 4. " ). ==! = A " 4 A " 6