3-3-1. Cisco dual BGP with AS prepend (Redundancy)

   April 9, 2008
BGP sample configuration 3-3-1

Cisco dual BGP with AS prepend (Redundancy)

   
  • ISPs : 1
  • WAN links : 2
  • CPE : 1
  • PE : 2
  • Device : Cisco router with LAN/WAN ports.
  • WAN1 / Serial IP : 12.1.3.0/30 (mask 255.255.255.252)
  • WAN2 / Serial IP : 12.1.4.0/30 (mask 255.255.255.252)
  • Destination IP : 100.100.100.100 and 200.200.200.200
  • LAN / Ethernet IP : 10.1.0.1/24 and 10.1.0.129/25(Secondary)
  • Receiving Route : Default route + full route from ISP
  • Memory : Full route(recommend 512M), partial route
    (recommend 128-256M)
  • LAN : ISP (AS20) and Customer (AS10)

 

BGP sample configuration 3-3-1

[Traffic flow]

Outbound traffic on CPE
 

All outbound traffic will go out thru primary line(12.1.3.1) due to secondary link has route-map shadow_inbound prepends AS twice on default route from BGP peer(12.1.4.2)

 

 
Inbound traffic on CPE
All inbound traffic will come in thru primary line (12.1.3.1) due to secondary link has route-map shadow_outbound prepends AS twice  on announcement to uplink.

[CPE/Customer Cisco Router]

Current configuration:
!
version 12.x
!
hostname CPE
!
interface Ethernet0
description to Internal network
ip address 10.1.0.1 255.255.255.0
ip address 10.1.0.129 255.255.255.128 secondary
no ip directed-broadcast
no ip mroute-cache
!
interface Serial0
description to ISP A – WAN 1
ip address 12.1.3.1 255.255.255.252
no ip directed-broadcast
no ip mroute-cache
no fair-queue
!
interface Serial1
description to ISP A – WAN 2
ip address 12.1.4.1 255.255.255.252
no ip directed-broadcast
no ip mroute-cache
no fair-queue
!
router bgp 10
no auto-summary
network 10.1.0.0 mask 255.255.255.0
neighbor 12.1.3.2 remote-as 20
neighbor 12.1.3.2 version 4
neighbor 12.1.3.2 prefix-list 1 out
neighbor 12.1.3.2 filter-list 10 out <– To prevent announcing routes that is learning from other link or ISP
neighbor 12.1.4.2 remote-as 20
neighbor 12.1.4.2 version 4
neighbor 12.1.4.2 prefix-list 1 out
neighbor 12.1.3.2 filter-list 10 out <– To prevent announcing routes that is learning from other link or ISP
neighbor 12.1.4.2 route-map shadow_inbound in
neighbor 12.1.4.2 route-map shadow_outbound out
!
ip classless
!
ip as-path access-list 10 permit ^$
! 
ip prefix-list 1 seq 5 permit 10.1.0.0/24
 

!
route-map shadow_inbound permit 10

 

set as-path prepend 10 10

 

!

 

route-map shadow_outbound permit 10

set as-path prepend 10 10
!
!
line con 0
line aux 0
line vty 0 4
login
!
end

[PE1 / ISP Cisco Router]

Current configuration:
!
version 12.x
!
hostname PE
!
!
interface Serial0
description to WAN 1
ip address 12.1.3.2 255.255.255.252
no ip directed-broadcast
no ip mroute-cache
no fair-queue
!
 

router bgp 20
no auto-summary
neighbor 12.1.3.1 remote-as 10
neighbor 12.1.3.1 version 4
neighbor 12.1.3.1 default-originate <—to send a default route

neighbor 12.1.3.1 distribute-list 2 out
!
ip classless
!
access-list 2 permit 100.100.100.0 0.0.0.255
access-list 2 permit 200.200.200.0 0.0.0.255 
! 
line con 0
line aux 0
line vty 0 4
login
!
end
[PE2 / ISP Cisco Router]
Current configuration:
!
version 12.x
!
hostname PE
!
!
interface Serial1
description to WAN 2
ip address 12.1.4.2 255.255.255.252
no ip mroute-cache
no ip directed-broadcast
no fair-queue
!
 

router bgp 20
no auto-summary
neighbor 12.1.4.1 remote-as 10
neighbor 12.1.4.1 version 4
neighbor 12.1.4.1 default-originate <—to send a default route

neighbor 12.1.4.1 distribute-list 2 out
!
ip classless
!
access-list 2 permit 100.100.100.0 0.0.0.255
access-list 2 permit 200.200.200.0 0.0.0.255
!
line con 0
line aux 0
line vty 0 4
login
!
end

 [Verifing output]

CPE#show ip bgp
BGP table version is 7, local router ID is 1.1.1.1
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
*> 0.0.0.0          12.1.3.2                 0             0 20 i
*                   12.1.4.2                 0             0 10 10 20 i
*> 10.1.0.0/24      0.0.0.0                  0         32768 i
*> 100.100.100.0/24 12.1.3.2                               0 20 ?
*                   12.1.4.2                               0 10 10 20 ?
*> 200.200.200.0    12.1.3.2                               0 20 ?
*                   12.1.4.2                               0 10 10 20 ?
CPE#
 

CPE# show ip bgp neighbors 12.1.3.2 ad
BGP table version is 7, local router ID is 1.1.1.1
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
*> 10.1.0.0/24      0.0.0.0                  0         32768 i

Total number of prefixes 1
CPE#
 

CPE# show ip bgp neighbors 12.1.4.2 ad
BGP table version is 7, local router ID is 1.1.1.1
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
*> 10.1.0.0/24      0.0.0.0                  0         32768 i

Total number of prefixes 1
CPE#

CPE# show ip bgp neighbors 12.1.3.2 ro
BGP table version is 7, local router ID is 1.1.1.1
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
*> 0.0.0.0          12.1.3.2                 0             0 20 i
*> 100.100.100.0/24 12.1.3.2                               0 20 ?
*> 200.200.200.0    12.1.3.2                               0 20 ?

Total number of prefixes 3
CPE#

CPE# show ip bgp neighbors 12.1.4.2 ro
BGP table version is 7, local router ID is 1.1.1.1
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
*  0.0.0.0          12.1.4.2                 0             0 10 10 20 i
*  100.100.100.0/24 12.1.4.2                               0 10 10 20 ?
*  200.200.200.0    12.1.4.2                               0 10 10 20 ?

Total number of prefixes 3
CPE# 

PE1#show ip bgp nei 12.1.3.1 ro
BGP table version is 58, local router ID is 3.3.3.3
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
*> 10.1.0.0/24      12.1.3.1                 0             0 10 i

Total number of prefixes 1
PE1#

 
 
PE2#show ip bgp nei 12.1.4.1 ro
BGP table version is 90, local router ID is 4.4.4.4
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
*> 10.1.0.0/24      12.1.4.1                 0             0 10 10 10 i

Total number of prefixes 1
PE2#
 

 
PE1#show ip bgp nei 12.1.3.1 ad
BGP table version is 58, local router ID is 3.3.3.3
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
*>i100.100.100.0/24 5.5.5.5                  0    100      0 ?
*>i200.200.200.0    5.5.5.5                  0    100      0 ?

Total number of prefixes 2
PE1#

 

PE2#show ip bgp nei 12.1.4.1 ad
BGP table version is 90, local router ID is 4.4.4.4
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
*>i100.100.100.0/24 5.5.5.5                  0    100      0 ?
*>i200.200.200.0    5.5.5.5                  0    100      0 ?

Total number of prefixes 2
PE2#

Internet#traceroute 10.1.0.1

Type escape sequence to abort.
Tracing the route to 10.1.0.1

  1 PE1 (20.3.5.1) 20 msec 28 msec 28 msec
  2 CPE (12.1.3.1) 56 msec *  64 msec

 

Internet#traceroute 10.1.0.129

Type escape sequence to abort.
Tracing the route to 10.1.0.129

  1 PE1 (20.3.5.1) 20 msec 28 msec 28 msec
  2 CPE (12.1.3.1) 52 msec *  52 msec
XR1#

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Author: Chris Yoon

IT professional