1-BGP HP

2 0 0 7 C i s c o S y s t e m s , I n c . A l l r i g h t s r e s e r v e d . C i s c o C o n f i d e n t i a l 1

BGP4


Agenda

Concept P eer i ng A ttr i b u tes a nd R ou te S el ecti on A l g or i th m P r ef i x G ener a ti on a nd A g g r eg a ti on P ol i cy Contr ol I nter na l B G P R ou te R ef l ector


C o n c e p t s


C o nc ep t s - Au t o no m o u s S y s t em

A s et of netw or k s s h a r i ng th e s a m e r ou ti ng pol i cy I nter na l connecti v i ty ( I G P ) R a ng e f or m 1 to 6 5 , 5 3 5( pr i v a te f r om 6 4 5 1 2 to 6 5 5 3 5 )

OSPFEI G R PI SI S

AS 1 2 3


C o nc ep t s - P at h V ec t o r P r o t o c o l B G P i s cl a s s i f i ed a s a path vector r ou ti ng pr otocol ( s e e R FC 1 3 2 2 )

A path vector protocol defines a route as a pairing between a destination and the attributes of the path to that destination.P revent loops via AS num ber

12.6.126.0/24 207.126.96.43 1021 0 6461 7018 6337 11268

AS PathAS Path


C o nc ep t s - B G P S es s i o ns

B G P s es s i on es ta b l i s h ed on top of T CP por t 1 7 9 ( B G P nei g h b or s )

R el i a b l e tr a ns por t l a y er ( no need of r etr a ns m i s s i ons a t B G P l a y er )

T CP need s a r ou ti ng l a y er ( I G P or s ta ti c) B G P u s es a d a ta b a s e ( B G P ta b l e) D a ta b a s es a r e ex ch a ng ed a f ter s es s i on s et u p I ncr em enta l u pd a tes B G P s es s i on i s m a i nta i ned w i th B G P k eepa l i v es ( 6 0 s )


eB G P i s u s ed to ex ch a ng e N L R I b etw een A u tonom ou s S y s tem s

i B G P i s u s ed to ca r r y N L R I w i th i n th e A u tonom ou s S y s tem

A B G P r ou ter h a s i nter na l a nd / or ex ter na l nei g h b or s

C o nc ep t s - eB G P v s i B G P


C o nc ep t s - G ener al O p er at i o n

L ea r ns m u l ti pl e pa th s v i a i nter na l a nd ex ter na l B G P s pea k er s

P i ck s T H E b es tpa th a nd i ns ta l l s i t i n th e I P f or w a r d i ng ta b l e

P ol i ci es a ppl i ed b y i nf l u enci ng th e b es tpa th s el ecti on b a s ed on B G P a ttr i b u tes :

P art of the B G P update pack etI m plem ented as T L V ( T y pe-L ength-V alue)


Pe e r i n g


E x t er nal N ei gh b o r s ( eB G P )

AS 1 0 9

AS 1 1 0

131.108.0.0/16A

B

15 0.10.0.0/16

131.108.10.0/2 4.1

.2

BGP speakers in different AS Sh o u l d b e direc tl y c o nnec ted C o nfig u ratio n:

R outer Brouter bgp 1 1 0network 1 5 0 . 1 0 . 0 . 0 neighbor 1 3 1 . 1 0 8 . 1 0 . 1 rem ote-as 1 0 9R outer Arouter bgp 1 0 9network 1 3 1 . 1 0 8 . 0 . 0 neighbor 1 3 1 . 1 0 8 . 1 0 . 2 rem ote-as 1 1 0

R B

R A


I nt er nal N ei gh b o r s ( i B G P )

Configuration:Router Brouter b g p 1 0 9n ei g h b or 1 3 1 . 1 0 8 . 2 0 . 2 rem ote-a s 1 0 9n ei g h b or 1 3 1 . 1 0 8 . 2 0 . 2 up d a te-s ourc e l oop 0Router Arouter b g p 1 0 9n ei g h b or 1 3 1 . 1 0 8 . 2 0 . 1 rem ote-a s 1 0 9n ei g h b or 1 3 1 . 1 0 8 . 2 0 . 1 up d a te-s ourc e l oop 0

A B131.108.2 0.2

131.108.2 0.1


I nf o r m at i o n T r ans f er

F r om eB G P -> a d v er ti s e to a l l F r om i B G P -> a d v er ti s e onl y to eB G P

full iB G P m esh is req uired!! P r opa g a te O N L Y th e b es t pa th


P eer G r o u p s

Gro u p o f peers to w h ic h th e sam e o u tb o u nd po l ic ies appl yonly inbound policies can be overriddenupdat es g enerat ed once per g roup

Sim pl ic ity o f c o nfig u ratio n


P eer G r o u p s ( C o nt . )

I nter na l peer g r ou prouter bgp 109n ei gh bor i n tern a l peer-groupn ei gh bor i n tern a l rem ote-a s 109n ei gh bor i n tern a l route-m a p s en d outn ei gh bor i n tern a l f i l ter-l i s t 1 outn ei gh bor 13 1. 108 . 2 0. 1 peer-group i n tern a ln ei gh bor 13 1. 108 . 3 0. 1 peer-group i n tern a l n ei gh bor 13 1. 108 . 3 0. 1 f i l ter-l i s t 3 i n

E x ter na l peer g r ou prouter bgp 109n ei gh bor ex tern a l -peer peer-groupn ei gh bor ex tern a l -peer route-m a p s et-m etri c outn ei gh bor 16 0. 8 9. 1. 2 rem ote-a s 2 00n ei gh bor 16 0. 8 9. 1. 2 peer-group ex tern a l -peern ei gh bor 16 0. 8 9. 1. 4 rem ote-a s 3 00n ei gh bor 16 0. 8 9. 1. 4 peer-group ex tern a l -peer


A t t r i b u t e s a n d R o u t e S e l e c t i o n A l g o r i t h m


M ai n B G P At t r i b u t es

Next-h o p W ei g h t L o c a l p r ef er en c e A S -p a th O r i g i n M u l ti E xi t D i s c r i m i n a to r ( M E D ) C o m m u n i ty


AS 22.0.0.0

B

A1 .0.0.0

2.0.1 .0

.1

.2

N E X T _ H O P

T h e nex t h o p to reac h a netw o rkeB G P

I P address of t h e peeriB G P

N E X T _ H O P advert ised by eB G PI G P sh ould carry rout e t o N E X T _ H O P sR ecursive rout e look upU nlink s B G P f rom t h e ph ysical t opolog yA llow s I G P t o m ak e int ellig entf orw arding decision AS 1C


O v e r r i d i n g d e f a u l t s :I BG P N L R I o n l y :n e i g h b o r x .x .x .x n e x t -h o p -s e l fr o u t e -m a p :s e t i p n e x t -h o p { A.B.C .D | p e e r a d d r e s s }

O v e r r i d i n g d e f a u l t s :I BG P N L R I o n l y :n e i g h b o r x .x .x .x n e x t -h o p -s e l fr o u t e -m a p :s e t i p n e x t -h o p { A.B.C .D | p e e r a d d r e s s }

AS 1 AS 22 .0.0.0/8 EE

FF

4 .0.0.0/8AS 4AS 3AA

CC

DD

BB

5 .1 .1 .1

6 .0.1 .1 6 .0.1 .2E BG P n e x t -h o p s e t t o s e l f

3 r d P a r t y E BG P 5 .1 .1 .2 5 .1 .1 .3 I BG P n e x t -h o p u n m o d i f i e d

4 .0.0.0/ 8 6 .0.1 .12.0.0.0/ 8 6 .0.1 .1

4 .0.0.0/ 8 5 .1 .1 .36.0.0.0/8

B G P At t r i b u t es : N E X T _ H O P


W E I G H T ci s co s peci f i c L oca l to th e r ou ter

N ot propag at ed v a l u e: 0 6 5 5 3 5 R ou tes w i th h i g h er w ei g h t a r e pr ef er r ed D ef a u l t:

orig inat ed locally = 3 2 7 6 8ot h er = 0


L O C AL _ P R E F

I nd i ca ti on of pr ef er r ed pa th to ex i t th e l oca l A S G l ob a l to th e l oca l A S P a th s w i th h i g h es t L O CA L -P R E F a r e m os t d es i r a b l e ( d ef a u l t = 1 0 0 )

bgp default local-preference value


L O C AL _ P R E F ( C o nt . )

C o nfig u ratio n ( rtr A) :router bgp 1 0 9neighbor x . x . x . x rem ote-as 1 8 8 0neighbor x . x . x . x route-m ap foo in!route-m ap foo perm it 1 0m atch as-path 2set local-preference 1 20!ip as-path access-list 2 perm it ^ 1 8 8 0 _

A

1 7 5 5 1 8 8 0

6 6 6N e e d s t o g o t o 6 9 0

6 9 0


A S -P A T H conta i ns th e l i s t of A S es th e u pd a te h a d to tr a v er s e.

A S -P A T H i s u pd a ted b y th e s end i ng r ou ter w i th i ts ow n A S nu m b er .

B G P u s es th e A S -P A T H to d etect r ou ti ng l oops . E a ch ti m e th e r ou ter r ecei v es a n eB G P u pd a te i t ch eck s th e A S -P A T H .

I f i t f i nd s i s ow n A S nu m b er on th e A S -P A T H , th e u pd a te i s d i s ca r d ed .

AS _ P AT H


1 8 8 0

14 1.2 5 3.10.0/2 4

A

6 9 0 B

200C

1. R o u t e r A s e n d s u p d a t e f o r14 1.2 5 3.10.0/2 4 w i t h AS _ P AT H : 1880

1. R o u t e r A s e n d s u p d a t e f o r14 1.2 5 3.10.0/2 4 w i t h AS _ P AT H : 1880

2 . R o u t e r B s e n d s u p d a t e f o r 14 1.2 5 3.10.0/2 4 w i t hAS _ P AT H : 69 0 1880

2 . R o u t e r B s e n d s u p d a t e f o r 14 1.2 5 3.10.0/2 4 w i t hAS _ P AT H : 69 0 1880

3.R o u t e r C s e n d s u p d a t e f o r 14 1.2 5 3.10.0/2 4 w i t h AS _ P AT H : 2 00 69 0 1880

3.R o u t e r C s e n d s u p d a t e f o r 14 1.2 5 3.10.0/2 4 w i t h AS _ P AT H : 2 00 69 0 1880

4 .R o u t e r A w i l l d e t e c t i t s o w n AS n u m b e r a n d w i l ld i s c a r d t h e u p d a t e

4 .R o u t e r A w i l l d e t e c t i t s o w n AS n u m b e r a n d w i l ld i s c a r d t h e u p d a t e

AS _ P AT H


O R I G I N

O r i g i n of th e pr ef i x V a l u es :

I G P ( i) = via network com m andE G P ( e) = learned from E G Pincom plete ( ? ) = redistribution


M u l t i -E x i t D i s c r i m i nat o r ( M E D )

Indication (to external peers) of the preferred path into an A S

used in m ultiple entry ASnon-transitive

C om pared only for rou tes from the sam e A S L ow er M E D v alu e is m ore preferab le (defau lt = 0 )


C o m m u ni t y At t r i b u t e

U s ed to g r ou p d es ti na ti ons a nd a ppl y a com m on pol i cy E a ch pr ef i x ca n b el ong to m u l ti pl e com m u ni ti es N ot pr opa g a ted b y d ef a u l t

neighbor i p -ad d r es s send-com m unity

rfc1997


C o m m u ni t y At t r i b u t e ( C o nt . ) 3 2 -b i ts l ong

use 16 bits to indicate the ASNip bg p -com m unity new -f or m atset com m unity AS:community [ additiv e]set com m unity none

er ase al l the v al ues in the attr ibuteset com m -l ist < num ber > del ete

er ase sel ected com m unities


ISP 1ISP 1

Cu s t o m e r 1Co n n e x i o n T y p e 1

( N o D e f a u l t ,W a n t s F u l l R o u t e s )

ISP 2

Co m m u n i t i e s :1 : 1 00Cu s t o m e r R o u t e s1 : 8 0 I S P R o u t e s


I SP 4I SP 3

Cu s t o m e r 1Co n n e x i o n T y p e 2( U s e s D e f a u l t ,

W a n t s Cu s t o m e r R o u t e s )

0.0.0.0

P r o b l em : S c al e R o u t i ng P o l i c yS o l u t i o n: C O M M U N I T Y


ISP 1ISP 1

Cu s t o m e r 1Co n n e x i o n T y p e 1

( N o D e f a u l t ,W a n t s F u l l R o u t e s )

Cu s t o m e r 2Co n n e x i o n T y p e 2( U s e s D e f a u l t ,

W a n t s Cu s t o m e r R o u t e s )

ISP 2M a t c h Co m m u n i t y

1 : 1 00

M a t c h Co m m u n i t y1 : 1 00 1 : 8 0 M a t c h Co m m u n i t y1 : 1 00

S e t Co m m u n i t y1 : 8 0

S e t Co m m u n i t y 1 : 1 00

I SP 4I SP 30.0.0.0

P r o b l em : S c al e R o u t i ng P o l i c yS o l u t i o n: C O M M U N I T Y




B G P P at h S el ec t i o n

1 O nl y c o nsider path s w ith reac h ab l e N E X T _ H O Ps 2 D o no t c o nsider iBGP path if no t sy nc h ro niz ed 3 H ig h est W E I GH T 4 H ig h est L O C AL _ PR E F 5 Prefer l o c al l y o rig inated ro u te 6 Sh o rtest AS_ PAT H


B G P P at h S el ec t i o n 7 L o w est O R I GI N c o de: I GP < E GP < inc o m pl ete 8 L o w est M u l ti-E x it D isc rim inato r ( M E D )

8 a I F b g p d eter m i ni s ti c-m ed , or d er th e pa th s b ef or e com pa r i ng

8 b I F b g p a l w a y s -com pa r e-m ed , th en com pa r e i t f or a l l pa th s

8 c Cons i d er ed onl y i f pa th s a r e f r om th e s a m e nei g h b or A S

9 Prefer an External path o v er an I nternal o ne 1 0 L o w est I GP m etric to th e N E X T _ H O P


B G P P at h S el ec t i o n ( C o nt . )

1 1 I F m u l tipath is enab l ed, th e ro u ter m ay instal l u p to N paral l el path s in th e ro u ting tab l e

1 2 F o r eBGP path s, sel ec t th e o l dest to m inim iz ero u te-fl ap

1 3 L o w est R o u ter-I DO r i g i na tor -I D i s cons i d er ed f or r ef l ected r ou tes

1 4 Sh o rtest C l u ster-L ist 1 5 L o w est neig h b o r I P address D e tail s giv e n : h ttp :/ / w w w . c is c o. c om / w arp / p ub l ic / 4 5 9 / 2 5 . s h tm l # b e s tp ath


Pr e f i x Ge n e r a t i o n A n d A g g r e g a t i o n


< net w o r k > C o m m and

N e t w o r k s o r i g i n a t e d b y t h e l o c a l r o u t e r M a t c h i n g I GP r o u t e m u s t e x i s t ( d y n a m i c o r s ta ti c en tr y i n r o u ti n g ta b l e)

E x a m p l e :route r b gp 1 0 9ne tw ork 2 0 0 . 1 0 . 1 0 . 0ne tw ork 1 9 8 . 1 0 . 0 . 0 m as k 2 5 5 . 2 5 5 . 0 . 0!ip route 1 9 8 . 1 0 . 0 . 0 2 5 5 . 2 5 5 . 0 . 0 nul l 0


R edi s t r i b u t i o n

F r o m I G PN ot alw ays a g ood t h ing !B y def ault , includes only local rout e ( not O S P F ex t ernal)

S ta ti c r o u tes p o i n ted to n u l l 0 E xa m p l e:

router bgp 109red i s tri bute s ta ti c!i p route 198 . 10. 0. 0 2 5 5 . 2 5 5 . 0. 0 n ul l 0


Aggr egat e Addr es s es

Com b i ne d i f f er ent r ou tes i nto one A d v er ti s ed a s com i ng f r om th e l oca l A S A com ponent m u s t ex i s t i n th e B G P ta b l e W ith no o ptio ns it pro pag ates th e ag g reg ate and al l th e c o m po nents

su m m ary -o nl y c o m m and o ptio nA dvert ise O N L Y t h e ag g reg at e ( no com ponent s)E x am ple:

route r b gp 1 0 9aggre gate -ad d re s s 1 9 8 . 1 0 . 0 . 0 2 5 5 . 2 5 5 . 0 . 0 s um m ary -onl y


Po l i c y C o n t r o l


P r ef i x F i l t er s

E x am pl e 1 :r outer bg p 10 9neig hbor 160 . 8 9 . 1. 1 distr ibute-l ist 5 in!access-l ist 5 deny 17 0 . 10 . 0 . 0access-l ist 5 p er m it any

E x am pl e 2 :r outer bg p 10 9neig hbor 160 . 8 9 . 1. 1 r oute-m ap f il ter in!r oute-m ap f il ter p er m it 10m atch ip addr ess 5!access-l ist 5 deny 17 0 . 10 . 0 . 0access-l ist 5 p er m it any


P at h F i l t er s

F i l ter b a s ed on A S pa thi p a s -pa th a c c es s -l i s t number [ perm i t| d en y ] reg ex p

P er nei g h b orI nbound or outboundfilter-listroute-m aps


P at h F i l t er s

E xam ple:D eny a l l pr ef i x es or i g i na ted i n A S 2 0 0 .

C onfig u ration:router bgp 109n ei gh bor 16 0. 8 9. 1. 1 rem ote-a s 3 00n ei gh bor 16 0. 8 9. 1. 1 f i l ter-l i s t 5 i n!i p a s -pa th a c c es s -l i s t 5 d en y _ 2 00$i p a s -pa th a c c es s -l i s t 5 perm i t . *


I n t e r n a l BGP


I nt er nal B G P

U sed to carry N L R I w ithin the A u tonom ou s S y stem R em em b er: B G P detects loops u sing the A S -P A T H B G P u pdates are sent u nchang ed to internal peers (no A S _ P A T H u pdate)

N o A S _ P A T H check is done w ith iB G P


I nt er nal B G P

iB G P speak ers cannot detect rou ting loopsiB G P is N E V E R propag ated T herefore iB G P req u ires a fu ll m esh

All BGP routers need an i BGP sessi on w i th eac h ex i t-p oi nt


R o u t e R e f l e c t o r s


R o u t e R ef l ec t o r s P r ov i d e a d d i ti ona l contr ol to a l l ow r ou ter to a d v er ti s e ( r ef l ect) i B G P l ea r ned r ou tes to oth er i B G P peer s

B reak s the full-m esh iB G P rule. N or m a l B G P s pea k er s co-ex i s t

only the R R has to support this feature cl u s ter = R R + cl i ents P a ck et f or w a r d i ng s h ou l d not b e a f f ected E a s y m i g r a ti on M u l ti pl e r ef l ector s f or r ed u nd a ncy Cl i ents ca n peer w i th i n m u l ti pl e cl u s ter s


R o u t e R ef l ec t o r s

R oute R ef lec tor: p rov i des addi ti onal c ontrol to allow router to adv erti se ( ref lec t) i BGP learned routes to oth er i BGP p eers

C li ent: router rely i ng on R R f or all i BGP up dates N on-c li ent: i BGP nei g h b or outsi de th e c luster C luster: S et of one or m ore R R s and th ei r c li ents


L o o p Av o i danc e

W h en R R r ecei v es a n u pd a te:C heck if its cluster-id is on the cluster-listI f cluster-id is on the cluster-list the update is silently discardedI f the B G P update is ok , the R R updates the cluster-list with its cluster-id and reflects the update ( according to the rules)W ith m ultiple R R in the sam e cluster, auniq ue cluster-id should be set by configuration

O nce th e b es t pa th i s s el ected :F rom non-client -> reflect to all clientsF rom client -> reflect to all clients AN D non clientsF rom eB G P peer -> reflect to all clients AN D non-clients


R o u t e R ef l ec t o r s ( c o nt . )

B CAS1

A ( R R )

AS2

C onf ig ur ation ( r tr A) :router bgp 2n ei gh bor 1 4 1 . 1 5 3 . 1 2. 1 rem ote-a s 2n ei gh bor 1 4 1 . 1 5 3 . 1 2. 1 route-ref l ec tor-c l i en tn ei gh bor 1 4 1 . 1 5 3 . 1 7 . 2 rem ote-a s 2n ei gh bor 1 4 1 . 1 5 3 . 1 7 . 2 route-ref l ec tor-c l i en t


M u l t i p l e R R p er C l u s t er

U s ed f or R R r ed u nd a ncy A l l R R s i n s a m e cl u s ter h a v e to a g r ee on u ni q u e cl u s ter -i d i f cl i ents peer w i th a l l R R s :

bgp cluster-id < 1 -232> T r ea t oth er R R s i n s a m e cl u s ter a s i B G P peer s ( i B G Pf u l l m es h )

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