4-2-1. Cisco dual BGP with prefix Length (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 : 100.100.100.0/23
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)
[Read this first]
This idea wouldn't be a good idea, if you only have a /24 IP block and announcing /25(more specific block) to one of ISP link. Why? most of ISP not accept smaller than /24 IP block from peers. So if you announce /25 from /24 to one of ISP link, the IP block won't be propagated to other ISP.
It won't work with smaller blocks(/25 below) due to ISP's default routing policy
If you have bigger than IP block /23 then it is doable solution see below example.
[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 100.100.100.0/23 except 100.100.101.0/24 will route to ISP_"A" due to 100.100.101.0/24 is more specific block than /23. So in this example half of /23 traffic is routed to each ISP links.
[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
!
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 <-------------- Connected to switch
ip address 100.100.101.1 255.255.255.0 secondary
ip address 100.100.100.1 255.255.254.0
duplex auto
speed auto
!
router bgp 10
no synchronization
bgp log-neighbor-changes
redistribute connected
neighbor 10.20.1.2 remote-as 20
neighbor 10.20.1.2 prefix-list traffic-1 out
neighbor 10.30.1.2 remote-as 30
neighbor 10.30.1.2 prefix-list traffic-2 out
neighbor 10.30.1.2 route-map traffic-2 out <------------- failover and load-sharing for /23 IP block.
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 traffic by destination
!
ip prefix-list traffic-1 description whole block only
ip prefix-list traffic-1 seq 5 permit 100.100.100.0/23
!
ip prefix-list traffic-2 description whole + specific block
ip prefix-list traffic-2 seq 5 permit 100.100.100.0/23 le 32
!
route-map traffic-2 permit 10 <------------ This route-map add AS prepending on announcement to ISP_"B" in order to make failover and load-sharing for /23 IP block.
match ip address prefix-list traffic-2
set as-path prepend 10
!
line con 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
!
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
neighbor 10.20.1.1 route-map no-routes out <---- Not sending any route to CPE
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 <---- Not sending any route to CPE
!
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
!
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
neighbor 10.30.1.1 route-map no-routes out <---- Not sending any route to CPE
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 <---- Not sending any route to CPE
!
line con 0
exec-timeout 0 0
logging synchronous
line aux 0
line vty 0 4
login
!
end
[Verifing output]
CPE#sh ip bgp | inc 100.100 BGP table version is 16, local router ID is 100.100.100.1 *> 100.100.100.0/23 0.0.0.0 0 32768 i *> 100.100.101.0/24 0.0.0.0 0 32768 i
CPE#sh ip bgp nei 10.20.1.2 ad BGP table version is 16, 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 *> 100.100.100.0/23 0.0.0.0 0 32768 i
Total number of prefixes 1
CPE#sh ip bgp nei 10.30.1.2 ad BGP table version is 16, 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 *> 100.100.100.0/23 0.0.0.0 0 32768 i *> 100.100.101.0/24 0.0.0.0 0 32768 i
Total number of prefixes 2 CPE#
ISP_A#sh ip bgp nei 10.20.1.1 ro BGP table version is 32, 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
*> 100.100.100.0/23 10.20.1.1 0 0 10 i
Total number of prefixes 1
ISP_A#
ISP_B#sh ip bgp nei 10.30.1.1 ro BGP table version is 44, 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
*> 100.100.100.0/23 10.30.1.1 0 0 10 10 i
*> 100.100.101.0/24 10.30.1.1 0 0 10 10 i
Total number of prefixes 2
ISP_B#
TR_A#sh ip bgp 100.100.101.2 BGP routing table entry for 100.100.101.0/24, version 29
Paths: (2 available, best #2, table Default-IP-Routing-Table)
Flag: 0x820
Advertised to update-groups:
1 2
50 30 10 10
20.50.1.2 from 20.50.1.2 (30.50.1.2)
Origin IGP, localpref 100, valid, external
30 10 10
20.30.1.2 from 20.30.1.2 (30.50.1.1)
Origin IGP, localpref 100, valid, external, best
TR_A#
TR_A#sh ip bgp 100.100.101.2 BGP routing table entry for 100.100.101.0/24, version 29
Paths: (2 available, best #2, table Default-IP-Routing-Table)
Advertised to update-groups:
1 2
50 30 10 10
20.50.1.2 from 20.50.1.2 (30.50.1.2)
Origin IGP, localpref 100, valid, external
30 10 10
20.30.1.2 from 20.30.1.2 (30.50.1.1)
Origin IGP, localpref 100, valid, external, best
TR_A#sh ip bgp 100.100.100.2 BGP routing table entry for 100.100.100.0/23, version 27
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#
TR_B#sh ip bgp 100.100.101.2 BGP routing table entry for 100.100.101.0/24, version 39
Paths: (1 available, best #1, table Default-IP-Routing-Table)
Advertised to update-groups:
2
10 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#sh ip bgp 100.100.100.2 BGP routing table entry for 100.100.100.0/23, version 37
Paths: (3 available, best #1, table Default-IP-Routing-Table)
Advertised to update-groups:
1 2
20 10
20.30.1.1 from 20.30.1.1 (20.50.1.1)
Origin IGP, localpref 100, valid, external, best
50 20 10
30.50.1.2 from 30.50.1.2 (30.50.1.2)
Origin IGP, localpref 100, valid, external
10 10
10.30.1.1 from 30.30.1.1 (30.30.1.1)
Origin IGP, metric 0, localpref 100, valid, internal
TR_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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