BGP PECE routing with multihoming Site Of Origin.docx
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BGPPECEroutingwithmultihomingSiteOfOrigin
BGPPE-CEroutingwithmultihoming-SiteOfOrigin
尚未multihoming的初始配置
showconfigvirpe11|berouterbgp
routerbgp65001
neighborpepeer-group
neighborperemote-as65001
neighborpeupdate-sourceloopback0
neighbor172.20.1.201peer-grouppe
neighbor172.20.1.202peer-grouppe
!
address-familyvpnv4unicast
neighbor172.20.1.201activate
neighbor172.20.1.201next-hop-self
neighbor172.20.1.201send-communityextended
neighbor172.20.1.202activate
neighbor172.20.1.202next-hop-self
neighbor172.20.1.202send-communityextended
exit-address-family
!
address-familyipv4unicastvrffull_mesh_pe11_001
nosynchronization
noauto-summary
redistributeconnected
neighbor10.1.233.2remote-as65002
neighbor10.1.233.2as-override
exit-address-family
showconfigvirce233|berouterbgp
routerbgp65002
neighbor10.1.233.1remote-as65001
network10.233.1.0mask255.255.255.0
-----------------------------------------------------------------------------------
showconfigvirpe21|berouterbgp
routerbgp65001
neighborpepeer-group
neighborperemote-as65001
neighborpeupdate-sourceloopback0
neighbor172.20.1.201peer-grouppe
neighbor172.20.1.202peer-grouppe
!
address-familyvpnv4unicast
neighbor172.20.1.201activate
neighbor172.20.1.201next-hop-self
neighbor172.20.1.201send-communityextended
neighbor172.20.1.202activate
neighbor172.20.1.202next-hop-self
neighbor172.20.1.202send-communityextended
exit-address-family
!
address-familyipv4unicastvrffull_mesh_pe21_001
nosynchronization
noauto-summary
redistributeconnected
neighbor10.1.244.2remote-as65002
neighbor10.1.244.2as-override
exit-address-family
!
showconfigvirce244|berouterbgp
routerbgp65002
neighbor10.1.244.1remote-as65001
network10.244.1.0mask255.255.255.0
!
---------------------------------------------------------------------------------------
showconfigvirpe31|berouterbgp
routerbgp65001
neighborpepeer-group
neighborperemote-as65001
neighborpeupdate-sourceloopback0
neighbor172.20.1.201peer-grouppe
neighbor172.20.1.202peer-grouppe
!
address-familyvpnv4unicast
neighbor172.20.1.201activate
neighbor172.20.1.201next-hop-self
neighbor172.20.1.201send-communityextended
neighbor172.20.1.202activate
neighbor172.20.1.202next-hop-self
neighbor172.20.1.202send-communityextended
exit-address-family
!
address-familyipv4unicastvrffull_mesh_pe31_001
nosynchronization
noauto-summary
redistributeconnected
neighbor10.1.255.2remote-as65002
neighbor10.1.255.2as-override
exit-address-family
!
routerospf1
network172.21.0.00.0.255.255area0.0.0.0
!
address172.20.1.31area0.0.0.0
!
ERX-1410-Down:
pe31#showconfigvirce255|berouterbgp
routerbgp65002
neighbor10.1.255.1remote-as65001
network10.255.1.0mask255.255.255.0
!
------------------------------------------------------------------------------------------
上面配置值得注意的是只要CE采用的AS号是一样的，就要配置as-override,
ERX-1410-Down:
ce233#ping10.244.1.1
Sending5ICMPechoesto10.244.1.1,timeout=2sec.
!
!
!
!
!
Successrate=100%（5/5）,round-tripmin/avg/max=3/3/4ms
ERX-1410-Down:
ce233#ping10.255.1.1
Sending5ICMPechoesto10.255.1.1,timeout=2sec.
!
!
!
!
!
Successrate=100%（5/5）,round-tripmin/avg/max=3/3/4ms
ERX-1410-Down:
ce233#showipbgp10.244.1.0/24
BGProuteinformationforprefix10.244.1.0/24
Receivedroutelearnedfromexternalpeer10.1.233.1（bestroute）
RouteplacedinIPforwardingtable
RouteplacedinIPbutnotusedasbesttunnel-route
Besttoadvertisetobothinternalandexternalpeers
AddressFamilyIdentifier（AFI）isip-v4
SubsequentAddressFamilyIdentifier（SAFI）isunicast
NexthopIPaddressis10.1.233.1（metric0）
Multi-exitdiscriminatorisnotpresent
Localpreferenceisnotpresent
Weightis0
OriginisIGP
ASpathis6500165001
ERX-1410-Down:
ce233#
以上配置尚未体现multihoming.下面我们将CE244和CE255连接起来.
ERX-1410-Down:
pe31#configt
Enterconfigurationcommands,oneperline. Endwith^Z.
ERX-1410-Down:
pe31（config）#virce244
ERX-1410-Down:
ce244（config）#intf0/2.2245
ERX-1410-Down:
ce244（config-if）#vlanid245
ERX-1410-Down:
ce244（config-if）#ipadd10.1.245.1/30
ERX-1410-Down:
ce244（config-if）#virce255
ERX-1410-Down:
ce255（config）#intf0/3.2245
ERX-1410-Down:
ce255（config-if）#vlanid245
ERX-1410-Down:
ce255（config-if）#ipadd10.1.245.2/30
ERX-1410-Down:
ce255（config-if）#doping10.1.245.1
Sending5ICMPechoesto10.1.245.1,timeout=2sec.
!
!
!
!
!
Successrate=100%（5/5）,round-tripmin/avg/max=3/5/14ms
ERX-1410-Down:
ce255（config-if）#
ERX-1410-Down:
ce255（config-if）#routerbgp65002
ERX-1410-Down:
ce255（config-router）#neighbor10.1.245.1remote-as65002
ERX-1410-Down:
ce255（config-router）#virce244
ERX-1410-Down:
ce244（config）#routerbgp65002
ERX-1410-Down:
ce244（config-router）#nei10.1.245.2remote-as65002
ERX-1410-Down:
ce244（config-router）#end
ERX-1410-Down:
ce255#showipbgsummary
Messages Messages Prefixes
Neighbor ASState Up/downtime Sent Received Received
10.1.245.1 65002Established 00:
00:
26 6 6 10
10.1.255.1 65001Established 16:
27:
58 1980 1984 10
ERX-1410-Down:
ce255#
ERX-1410-Down:
ce244#showiproute10.255.1.0
Protocol/Routetypecodes:
I1-ISISlevel1,I2-ISISlevel2,
I-routetypeintra,IA-routetypeinter,E-routetypeexternal,
i-metrictypeinternal,e-metrictypeexternal,
O-OSPF,E1-externaltype1,E2-externaltype2,
N1-NSSAexternaltype1,N2-NSSAexternaltype2
L-MPLSlabel,V-VRF,*-viaindirectnext-hop
Prefix/Length Type NextHop Dst/Met Interface
---------------------------------------------------------------------------
10.255.1.0/24 Bgp 10.1.245.2* 200/0 FastEthernet0/2.2245
ERX-1410-Down:
ce244#showipbgp 10.255.1.0/24
BGProuteinformationforprefix10.255.1.0/24
Receivedroutelearnedfromexternalpeer10.1.244.1
RoutenotplacedinIPforwardingtable
Donotadvertisetoanypeers
AddressFamilyIdentifier（AFI）isip-v4
SubsequentAddressFamilyIdentifier（SAFI）isunicast
NexthopIPaddressis10.1.244.1（metric0）
Multi-exitdiscriminatorisnotpresent
Localpreferenceisnotpresent
Weightis0
OriginisIGP
ASpathis6500165001
Receivedroutelearnedfrominternalpeer10.1.245.2（bestroute）
RouteplacedinIPforwardingtable
RouteplacedinIPbutnotusedasbesttunnel-route
Besttoadvertisetoexternalpeers
AddressFamilyIdentifier（AFI）isip-v4
SubsequentAddressFamilyIdentifier（SAFI）isunicast
NexthopIPaddressis10.1.245.2（metric0）
Multi-exitdiscriminatoris0
Localpreferenceis100
Weightis0
OriginisIGP
ASpathisempty
ERX-1410-Down:
ce244#showipbgp10.255.1.0/24
Statuscodes:
>best,*invalid,ssuppressed,ddampened,rrejected,
aauto-summarized
Prefix Peer Next-hop MEDLocPrfWeightOrigin
10.255.1.0/24 10.1.244.1 10.1.244.1 0IGP
>10.255.1.0/24 10.1.245.2 10.1.245.2 0 100 0IGP
///一般不配置SOO的情况下,我们会发现此时CE244和CE255通信已经是走内部了,这就有个问题,如果不配置SOO,CE244是可以通过PE21学习到10.255.1.0/24的路由的,而且是EBGP,其优先值高,我们就奇怪为什么放到路由表的是IBGP路由呢?
///这时其实就涉及到BGP最优选路的问题,BGP的比较过程是WEIGHT--LOCALPREFENCE-LOCALORIGINATED-ASPATH-ORIGIN-MED-EBGP.这里面就是localpref胜出.
BGPdeterminesthebestpathtoeachdestinationforaBGPspeakerbycomparingpathattributesaccordingtothefollowingselectionsequence:
1Selectapathwithareachablenexthop.
2Selectthepathwiththehighestweight.
3Ifpathweightsarethesame,selectthepathwiththehighestlocalpreferencevalue.
4Preferlocallyoriginatedroutes（networkroutes,redistributedroutes,oraggregatedroutes）overreceivedroutes.
5SelecttheroutewiththeshortestAS-pathlength.
6IfallpathshavethesameAS-pathlength,selectthepathbasedonorigin:
IGPispreferredoverEGP;EGPispreferredoverIncomplete.
7Iftheoriginsarethesame,selectthepathwithlowestMEDvalue.
8IfthepathshavethesameMEDvalues,selectthepathlearnedbymeansofEBGPoveronelearnedbymeansofIBGP.
9SelectthepathwiththelowestIGPcosttothenexthop.
10Selectthepathwiththeshortestroutereflectionclusterlist.Routeswithoutaclusterlistaretreatedashavingaclusterlistoflength0.
11SelectthepathreceivedfromthepeerwiththelowestBGProuterID.
12Selectthepaththatwaslearnedfromtheneighborwiththelowestpeerremoteaddress.
为了防止潜在的路由循环,就需要配置S00.也就是说CE244不想从PE21学习到1
0.255.1.0/24的路由
access-list10permitipanyany
virpe21
access-list10permitipanyany
route-mapSOOpermit10
matchipaddress10
setextcommunitysoo1:
10
virpe31
access-list10permitipanyany
route-mapSOOpermit10
matchipaddress10
setextcommunitysoo1:
10
virpe31
routerbgp65001
address-familyipv4unicastvrffull_mesh_pe31_001
neighbor10.1.255.2route-mapSOOin
virpe21
routerbgp65001
address-familyipv4unicastvrffull_mesh_pe21_001
neighbor10.1.244.2route-mapSOOin
ERX-1410-Down:
pe21#showipbgpvpnv4all10.255.1.0/24
BGProuteinformationforprefix10.255.1.0/24
Receivedroutelearnedfromexternalpeer10.1.244.2（bestroute）
Leakedroute
RouteplacedinIPforwardingtablebutnotusedforforwarding
RouteplacedinIPbutnotus
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