Home BGP Configurations Cisco 6-1-2. Cisco dual BGP with AS prepend-iBGP (Load-sharing)

Cisco dual BGP with AS prepend-iBGP (Load-sharing)

   
  • ISPs : 2
  • WAN links : 2
  • CPE : 2
  • PE : 2
  • Device : Cisco router with LAN/WAN ports.
  • WAN1 / Serial IP : 10.20.1.0/30 (mask 255.255.255.252)
  • WAN2 / Serial IP : 10.30.1.0/30 (mask 255.255.255.252)
  • LAN / Ethernet IP : 100.100.100.0/24 and 200.200.200.0/24
  • Receiving Route : Default route from ISP
  • Memory : Full route(recommend 512M), partial route
    (recommend 128-256M), default route only in this sample.
  • LAN : ISP_A (AS20), ISP_B(AS30), Customer (AS10) and other ISP (AS50)

 

BGP sample configuration 6-1-1

 [Traffic flow]

Outbound traffic on CPE

In this sample, customer is receiving default route from ISPs and iBGP router(less preferred). By default route, outbound traffic of IP block 100.100.100.0/24 will be routed to ISP_"A" and traffic of IP block 200.200.200.0/24 will be routed to ISP_"B". When serial link is down, outbound traffic is routed thru iBGP peer.

Inbound traffic  on CPE

All traffic associated with 100.100.100.0/24 will be routed thru ISP_"A" and 200.200.200.0/24 will be routed thru ISP_"B". This configuration will cover failover situation and achieve load-sharing planl. One of line failed, other link will take both traffic by AS prepending BGP policy. See below example and testing output.

topology_BGP6-1-1.png 

[CPE_1/Customer Cisco Router]
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname CPE_1
!
ip cef
no ip domain lookup
!
interface FastEthernet0/0
 no ip address
 duplex auto
 speed auto
!
interface FastEthernet0/1
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface Serial1/0
 no ip address
 shutdown
 serial restart-delay 0
!
interface Serial1/1
 ip address 10.20.1.1 255.255.255.252
 load-interval 30
 serial restart-delay 0
!
interface Serial1/2
 no ip address
 load-interval 30
 shutdown
 serial restart-delay 0
!
interface Serial1/3
 no ip address
 shutdown
 serial restart-delay 0
!
interface FastEthernet2/0
 ip address 200.200.200.2 255.255.255.0 secondary
 ip address 100.100.100.1 255.255.255.0
 duplex auto
 speed auto
!
router bgp 10
 no synchronization
 bgp log-neighbor-changes
 network 100.100.100.0 mask 255.255.255.0
 network 200.200.200.0
 redistribute connected
 neighbor 10.20.1.2 remote-as 20 <------------------ BGP neighbor to ISP_"A"
 neighbor 10.20.1.2 prefix-list to-ISP out <--------- Allow only IP block need to be advertised to ISP
 neighbor 10.20.1.2 route-map route-to-ISP out <-------- To control inbound traffic
 neighbor 100.100.100.2 remote-as 10 <----------- iBGP neighbor to CPE_2
 neighbor 100.100.100.2 default-originate <------- Send default route
 neighbor 100.100.100.2 route-map route-to-ibgp in <------- Make less prefer
 no auto-summary
!
ip http server
no ip http secure-server
ip forward-protocol nd
!
ip prefix-list prefix-1 seq 5 permit 100.100.100.0/24
!
ip prefix-list prefix-2 seq 5 permit 200.200.200.0/24
!
ip prefix-list to-ISP seq 5 permit 100.100.100.0/24
ip prefix-list to-ISP seq 10 permit 200.200.200.0/24
!
route-map route-to-ISP permit 10 <-------- To control inbound traffic
 match ip address prefix-list prefix-2
 set as-path prepend 10 10 10

!
route-map route-to-ISP permit 20
!
route-map route-to-ibgp permit 10 <------- Make less prefer
 set local-preference 80
!
control-plane
!
line con 0
 exec-timeout 0 0
 logging synchronous
line aux 0
line vty 0 4
 login
!
end

[CPE_2/Customer Cisco Router]

version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname CPE_2
!
ip cef
no ip domain lookup
!
interface FastEthernet0/0
 ip address 200.200.200.4 255.255.255.0
 shutdown
 duplex auto
 speed auto
!
interface FastEthernet0/1
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface Serial1/0
 no ip address
 shutdown
 serial restart-delay 0
!
interface Serial1/1
 ip address 10.30.1.1 255.255.255.252
 load-interval 30
 serial restart-delay 0
!
interface Serial1/2
 no ip address
 shutdown
 serial restart-delay 0
!
interface Serial1/3
 no ip address
 shutdown
 serial restart-delay 0
!
interface FastEthernet2/0
 ip address 100.100.100.2 255.255.255.0 secondary
 ip address 200.200.200.1 255.255.255.0
 duplex auto
 speed auto
!
router bgp 10
 no synchronization
 bgp log-neighbor-changes
 network 100.100.100.0 mask 255.255.255.0
 network 200.200.200.0
 redistribute connected
 neighbor 10.30.1.2 remote-as 30 <------------------ BGP neighbor to ISP_"B"
 neighbor 10.30.1.2 prefix-list to-ISP out <--------- Allow only IP block need to be advertised to ISP
 neighbor 10.30.1.2 route-map route-to-ISP out <-------- To control inbound traffic
 neighbor 100.100.100.1 remote-as 10 <----------- iBGP neighbor to CPE_1
 neighbor 100.100.100.1 default-originate <------- Send default route
 neighbor 100.100.100.1 route-map route-to-ibgp in <------- Make less prefer
 no auto-summary
!
ip http server
no ip http secure-server
ip forward-protocol nd
!
ip prefix-list prefix-1 seq 5 permit 100.100.100.0/24
!
ip prefix-list prefix-2 seq 5 permit 200.200.200.0/24
!
ip prefix-list to-ISP seq 5 permit 100.100.100.0/24
ip prefix-list to-ISP seq 10 permit 200.200.200.0/24
!
route-map route-to-ISP permit 10 <-------- To control inbound traffic
 match ip address prefix-list prefix-1
 set as-path prepend 10 10 10

!
route-map route-to-ISP permit 20
!
route-map route-to-ibgp permit 10 <------- Make less prefer
 set local-preference 80
!
control-plane
!
line con 0
 exec-timeout 0 0
 logging synchronous
line aux 0
line vty 0 4
 login
!
end



 

[ISP_A PE/ISP Cisco Router]
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname ISP_A
!
ip cef
no ip domain lookup
!
interface FastEthernet0/0
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface FastEthernet0/1
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface Serial1/0
 ip address 10.20.1.2 255.255.255.252
 serial restart-delay 0
!
interface Serial1/1
 ip address 20.20.1.1 255.255.255.252
 serial restart-delay 0
!
interface Serial1/2
 no ip address
 shutdown
 serial restart-delay 0
!
interface Serial1/3
 no ip address
 shutdown
 serial restart-delay 0
!
router bgp 20
 no synchronization
 bgp log-neighbor-changes
 redistribute connected
 neighbor 10.20.1.1 remote-as 10 <------------------ BGP neighbor to Customer
 neighbor 10.20.1.1 default-originate
 neighbor 10.20.1.1 route-map no-routes out
<------- No BGP routes will be sent to Customer
 neighbor 20.20.1.2 remote-as 20
 no auto-summary
!
ip http server
no ip http secure-server
ip forward-protocol nd
!
route-map no-routes deny 10 <------- No BGP routes will be sent to Customer
!
control-plane
!
line con 0
 exec-timeout 0 0
 logging synchronous
line aux 0
line vty 0 4
 login
!
end

[ISP_B PE / ISP Cisco Router]

version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname ISP_B
!
ip cef
no ip domain lookup
!
interface FastEthernet0/0
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface FastEthernet0/1
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface Serial1/0
 ip address 10.30.1.2 255.255.255.252
 serial restart-delay 0
!
interface Serial1/1
 ip address 30.30.1.1 255.255.255.252
 serial restart-delay 0
!
interface Serial1/2
 no ip address
 shutdown
 serial restart-delay 0
!
interface Serial1/3
 no ip address
 shutdown
 serial restart-delay 0
!
router bgp 30
 no synchronization
 bgp log-neighbor-changes
 redistribute connected
 neighbor 10.30.1.1 remote-as 10 <------------------ BGP neighbor to Customer
 neighbor 10.30.1.1 default-originate
 neighbor 10.30.1.1 route-map no-routes out
<------- No BGP routes will be sent to Customer
 neighbor 30.30.1.2 remote-as 30
 no auto-summary
!
ip http server
no ip http secure-server
ip forward-protocol nd
!
route-map no-routes deny 10 <------- No BGP routes will be sent to Customer
!
control-plane
!
line con 0
 exec-timeout 0 0
 logging synchronous
line aux 0
line vty 0 4
 login
!
end

 [Verifing output]

CPE_1#sh ip bgp 0.0.0.0
BGP routing table entry for 0.0.0.0/0, version 21
Paths: (2 available, best #1, table Default-IP-Routing-Table)
  Not advertised to any peer
  20
    10.20.1.2 from 10.20.1.2 (20.20.1.1)
      Origin IGP, metric 0, localpref 100, valid, external, best
  Local
    100.100.100.2 from 100.100.100.2 (200.200.200.1)
      Origin IGP, metric 0, localpref 80, valid, internal



CPE_1#sh ip bgp nei 10.20.1.2 ad
BGP table version is 23, local router ID is 100.100.100.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
*> 100.100.100.0/24 0.0.0.0                  0         32768 i
*> 200.200.200.0    0.0.0.0                  0         32768 i

Total number of prefixes 2
CPE_1#



CPE_2#sh ip bgp 0.0.0.0
BGP routing table entry for 0.0.0.0/0, version 20
Paths: (2 available, best #1, table Default-IP-Routing-Table)
  Not advertised to any peer
  30
    10.30.1.2 from 10.30.1.2 (30.30.1.1)
      Origin IGP, metric 0, localpref 100, valid, external, best
  Local
    100.100.100.1 from 100.100.100.1 (100.100.100.1)
      Origin IGP, metric 0, localpref 80, valid, internal



CPE_2#sh ip bgp nei 10.30.1.2 ad
BGP table version is 20, local router ID is 200.200.200.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
*> 100.100.100.0/24 0.0.0.0                  0         32768 i
*> 200.200.200.0    0.0.0.0                  0         32768 i

Total number of prefixes 2
CPE_2#



ISP_A#sh ip bgp nei 10.20.1.1 ro
BGP table version is 56, local router ID is 20.20.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
*> 100.100.100.0/24 10.20.1.1                0             0 10 i
*  200.200.200.0    10.20.1.1                0             0 10 10 10 10 i

Total number of prefixes 2
ISP_A#



ISP_B#sh ip bgp nei 10.30.1.1 ro
BGP table version is 60, local router ID is 30.30.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
*  100.100.100.0/24 10.30.1.1                0             0 10 10 10 10 i
*> 200.200.200.0    10.30.1.1                0             0 10 i

Total number of prefixes 2
ISP_B#



TR_A#sh ip bgp 100.100.100.0
BGP routing table entry for 100.100.100.0/24, version 51
Paths: (1 available, best #1, table Default-IP-Routing-Table)
  Advertised to update-groups:
     1
  10
    10.20.1.1 from 20.20.1.1 (20.20.1.1)
      Origin IGP, metric 0, localpref 100, valid, internal, best



TR_A#sh ip bgp 200.200.200.0
BGP routing table entry for 200.200.200.0/24, version 58
Paths: (2 available, best #2, table Default-IP-Routing-Table)
  Advertised to update-groups:
     1          2
  50 30 10
    20.50.1.2 from 20.50.1.2 (30.50.1.2)
      Origin IGP, localpref 100, valid, external
  30 10
    20.30.1.2 from 20.30.1.2 (30.50.1.1)
      Origin IGP, localpref 100, valid, external, best
TR_A#



TR_B#sh ip bgp 100.100.100.0
BGP routing table entry for 100.100.100.0/24, version 61
Paths: (2 available, best #2, table Default-IP-Routing-Table)
  Advertised to update-groups:
     1          2
  50 20 10
    30.50.1.2 from 30.50.1.2 (30.50.1.2)
      Origin IGP, localpref 100, valid, external
  20 10
    20.30.1.1 from 20.30.1.1 (20.50.1.1)
      Origin IGP, localpref 100, valid, external, best



TR_B#sh ip bgp 200.200.200.0
BGP routing table entry for 200.200.200.0/24, version 66
Paths: (1 available, best #1, table Default-IP-Routing-Table)
  Advertised to update-groups:
     2
  10
    10.30.1.1 from 30.30.1.1 (30.30.1.1)
      Origin IGP, metric 0, localpref 100, valid, internal, best
TR_B#



Other_ISP#sh ip bgp 100.100.100.0
BGP routing table entry for 100.100.100.0/24, version 64
Paths: (2 available, best #1, table Default-IP-Routing-Table)
  Advertised to update-groups:
     1
  20 10
    20.50.1.1 from 20.50.1.1 (20.50.1.1)
      Origin IGP, localpref 100, valid, external, best
  30 20 10
    30.50.1.1 from 30.50.1.1 (30.50.1.1)
      Origin IGP, localpref 100, valid, external



Other_ISP#tr 100.100.100.3
Type escape sequence to abort.
Tracing the route to 100.100.100.3

  1 20.50.1.1 64 msec 28 msec 8 msec
  2 20.20.1.1 [AS 20] 40 msec 24 msec 4 msec
  3 10.20.1.1 [AS 20] 16 msec 20 msec 8 msec
  4 100.100.100.3 [AS 10] 44 msec *  40 msec



Other_ISP#sh ip bgp 200.200.200.0
BGP routing table entry for 200.200.200.0/24, version 71
Paths: (2 available, best #1, table Default-IP-Routing-Table)
  Advertised to update-groups:
     1
  30 10
    30.50.1.1 from 30.50.1.1 (30.50.1.1)
      Origin IGP, localpref 100, valid, external, best
  20 30 10
    20.50.1.1 from 20.50.1.1 (20.50.1.1)
      Origin IGP, localpref 100, valid, external



Other_ISP#tr 200.200.200.3
Type escape sequence to abort.
Tracing the route to 200.200.200.3

  1 30.50.1.1 52 msec 64 msec 12 msec
  2 30.30.1.1 [AS 30] 16 msec 20 msec 8 msec
  3 10.30.1.1 [AS 30] 12 msec 32 msec 16 msec
  4 200.200.200.3 [AS 10] 20 msec *  44 msec
Other_ISP#


 [Dynamips testing]

Download and test it yourself with below Dynamips configuration files.
  Dynamips NET file
  Router configuration files

If you have any questions, feel free to send email us at contactus@showipbgp.com. If you are looking for professional grade service, you might want to try our "BGP experts service". What is "BGP Experts service"? Click "BGP Experts" from the top menu option. You will find out what the "BGP Experts" and what we are doing here for.


 
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