4-5-1. Cisco dual BGP with Origin Value (Redundancy)
ISPs : 2
WAN links : 2
CPE : 1
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
Receiving Route : Default route only from ISP
Memory : Full route(recommend 512M), partial route
(recommend 128-256M)
LAN : ISP_A (AS20), ISP_B(AS30), Customer (AS10) and Other ISP(AS50)
[Read it first]
When you have more than two ISP links, Origin attribute option won't be enough to achieve failover and load-sharing goals.
why? simply shortest AS path is more prefer attribute than Origin attribute option on BGP selection criteria.
Below example we used AS-Path prepending for inbound traffic on shadow link which is connected to ISP_"B".
[Traffic flow]
Outbound traffic on CPE
Both links are receiving default route thru BGP, but on Shadow link CPE put AS prepending once to make less prefer. So outbound traffic will go out to ISP_"A" link all the time.
Inbound traffic on CPE
All traffic inbound traffic will be routed thru ISP_"A" link, b/c of Origin value is IGP on BGP announcement to ISP_"A" link, but incomplete on other BGP link. See below sample and testing output.
[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
!
ip auth-proxy max-nodata-conns 3
ip admission max-nodata-conns 3
!
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
serial restart-delay 0
!
interface Serial1/2
ip address 10.30.1.1 255.255.255.252
serial restart-delay 0
!
interface Serial1/3
no ip address
shutdown
serial restart-delay 0
!
interface FastEthernet2/0
ip address 100.100.100.1 255.255.255.0
duplex auto
speed auto
!
router bgp 10
no synchronization
bgp log-neighbor-changes
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 primary-out out
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 backup-in in <----- Prepending AS to default route from ISP to make less prefersed to ISP
neighbor 10.30.1.2 route-map backup-out out
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 to-ISP seq 5 permit 100.100.100.0/24
!
route-map backup-in permit 10
set as-path prepend 10
!
route-map primary-out permit 10
match ip address prefix-list prefix-1
set origin igp
!
route-map backup-out permit 10
match ip address prefix-list prefix-1
set as-path prepend 10
!
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 <-------------- Sending default route thru BGP
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
!
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 <-------------- Sending default route thru BGP
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
!
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#sh ip bgp nei 10.20.1.2 ad BGP table version is 5, 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 ?
Total number of prefixes 1
CPE#sh ip bgp nei 10.20.1.2 ro BGP table version is 5, 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#sh ip bgp nei 10.30.1.2 ad BGP table version is 5, 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 ?
Total number of prefixes 1
CPE#sh ip bgp nei 10.30.1.2 ro BGP table version is 5, 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 10.30.1.2 0 0 10 30 i
Total number of prefixes 1
CPE#
ISP_B#sh ip bgp 100.100.100.2 BGP routing table entry for 100.100.100.0/24, version 10
Paths: (2 available, best #1, table Default-IP-Routing-Table)
Not advertised to any peer
20 10
20.30.1.1 from 30.30.1.2 (30.50.1.1)
Origin IGP, metric 0, localpref 100, valid, internal, best
10 10
10.30.1.1 from 10.30.1.1 (100.100.100.1)
Origin incomplete, metric 0, localpref 100, valid, external
ISP_B#tr 100.100.100.2
Type escape sequence to abort.
Tracing the route to 100.100.100.2
Download and test it yourself with below Dynamips configuration files.
Dynamips NET file
Router configuration files
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BGP Configurations 
