4-3-2. Cisco dual BGP with AS prepend (Load-balancing)
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 and 200.200.200.0/24
Receiving Route : No BGP route table 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)
[Traffic flow]
Outbound traffic on CPE
In this sample, we are not receiving any BGP route table from ISP. We configured static routes are pointing to both serial links. Of cause it wouldn't be 50/50, due to packets will be routed by destination based.
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 as well. One of line failed, other link will take both traffic. See below example 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
!
boot-start-marker
boot-end-marker
!
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
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 200.200.200.1 255.255.255.0 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 traffic-1 out <----- Applied route-map on BGP session with ISP_"A" 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 traffic-2 out <----- Applied route-map on BGP session with ISP_"B"
no auto-summary
!
ip http server
no ip http secure-server
ip forward-protocol nd
!
ip route 0.0.0.0 0.0.0.0 Serial1/1 <------------- Load-sharing outbound trafficby destination ip route 0.0.0.0 0.0.0.0 Serial1/2 <------------- Load-sharing outbound trafficby destination
!
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 traffic-1 permit 10
match ip address prefix-list prefix-2
set as-path prepend 10 10 <-------- Prepending ASN 10 two times to announcement(200.200.200.0/24)
!
route-map traffic-1 permit 20 <------ Necessary this statement in order to pass thru route(100.100.100.0/24) !
route-map traffic-2 permit 10
match ip address prefix-list prefix-1
set as-path prepend 10 10 <-------- Prepending ASN 10 two times to announcement(100.100.100.0/24) !
route-map traffic-2 permit 20 <------ Necessary this statement in order to pass thru route(200.200.200.0/24)
!
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
!
boot-start-marker
boot-end-marker
!
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 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
!
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
!
boot-start-marker
boot-end-marker
!
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 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
!
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 10.30.1.2 ro BGP table version is 6, 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 30 i
Total number of prefixes 1
CPE#sh ip bgp nei 10.20.1.2 ro BGP table version is 6, 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 200.200.200.0 BGP routing table entry for 200.200.200.0/24, version 6
Paths: (1 available, best #1, table Default-IP-Routing-Table)
Advertised to update-groups:
1 2
Local
0.0.0.0 from 0.0.0.0 (100.100.100.1)
Origin IGP, metric 0, localpref 100, weight 32768, valid, sourced, local, best
CPE#sh ip bgp 100.100.100.0 BGP routing table entry for 100.100.100.0/24, version 5
Paths: (1 available, best #1, table Default-IP-Routing-Table)
Advertised to update-groups:
1 2
Local
0.0.0.0 from 0.0.0.0 (100.100.100.1)
Origin IGP, metric 0, localpref 100, weight 32768, valid, sourced, local, best
CPE#
ISP_A#sh ip bgp neighbors 10.20.1.1 ro BGP table version is 28, 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 i
Total number of prefixes 2
ISP_B#sh ip bgp neighbors 10.30.1.1 ro BGP table version is 32, 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 i
*> 200.200.200.0 10.30.1.1 0 0 10 i
Total number of prefixes 2
TR_A#sh ip bgp 100.100.100.0 BGP routing table entry for 100.100.100.0/24, version 22
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 23
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_B#sh ip bgp 100.100.100.0 BGP routing table entry for 100.100.100.0/24, version 26
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 24
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#
Internet#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 
