Home BGP Configurations Cisco 1-3-1. Cisco Single BGP with Origin value

Cisco Single BGP with Origin value

Lowest Origin Type is one of important criteria for BGP best path selection.

- Prefer the path with the lowest origin type: IGP is lower than EGP, and EGP is lower than INCOMPLETE. (IGP < EGP < Incomplete)
- IGP origin is created when there is a network statement
- EGP origin is created via รข€˜redistribute

- Incomplete origin is created via redistribute

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[CPE/Customer Cisco Router]
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname CPE
!
ip cef
no ip domain lookup
!
interface FastEthernet0/0
 ip address 100.100.100.1 255.255.255.0
 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
 no ip address
 shutdown
 duplex auto
 speed auto
!
router bgp 10
 no synchronization
 bgp log-neighbor-changes
 network 100.100.100.0 mask 255.255.255.0
 redistribute connected
 neighbor 10.20.1.2 remote-as 20 <--------------- BGP neighbor to ISP
 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
 no auto-summary
!
ip http server
no ip http secure-server
ip forward-protocol nd
!
ip prefix-list to-ISP seq 5 permit 100.100.100.0/24
!
route-map route-to-ISP permit 10 <------------ Change origin value to 'IGP'
 set origin igp
!
control-plane
!
line con 0
 exec-timeout 0 0
 logging synchronous
line aux 0
line vty 0 4
 login
!
end
[PE / ISP Cisco Router]
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname PE
!
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
 no ip address
 shutdown
 serial restart-delay 0
!
interface Serial1/1
 ip address 10.20.1.2 255.255.255.252
 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 ISP
 neighbor 10.20.1.1 default-originate <-------------- Send default route thru BGP
 neighbor 10.20.1.1 route-map no-routes out
 no auto-summary
!
ip http server
no ip http secure-server
ip forward-protocol nd
!
route-map no-routes deny 10
!
control-plane
!
line con 0
 exec-timeout 0 0
 logging synchronous
line aux 0
line vty 0 4
 login
!
end

 [Verifing output]

CPE#sh ip bgp nei 10.20.1.2 ad
BGP table version is 4, 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

Total number of prefixes 1


CPE#sh ip bgp nei 10.20.1.2 ro
BGP table version is 4, 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
*> 0.0.0.0          10.20.1.2                0             0 20 i

Total number of prefixes 1
CPE#


PE#sh ip bgp neighbors 10.20.1.1 ro
BGP table version is 3, local router ID is 10.20.1.2
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

Total number of prefixes 1


PE#sh ip bgp neighbors 10.20.1.1 ad
BGP table version is 3, local router ID is 10.20.1.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete

Originating default network 0.0.0.0

   Network          Next Hop            Metric LocPrf Weight Path

Total number of prefixes 0


PE#sh ip bgp 100.100.100.0
BGP routing table entry for 100.100.100.0/24, version 3
Paths: (1 available, best #1, table Default-IP-Routing-Table)
Flag: 0x820
  Not advertised to any peer
  10
    10.20.1.1 from 10.20.1.1 (100.100.100.1)
      Origin IG
P, metric 0, localpref 100, valid, external, best
PE#

[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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