3-4-1. Cisco dual BGP with Community string (Redundancy)

   April 9, 2008
BGP sample configuration 3-4-1

Cisco dual BGP with Community string (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 3-4-1

[Traffic flow]

Outbound traffic on CPE
All outbound traffic will go out thru primary line(12.1.3.1) due to primary link tagged weight 1000 all inbound announcement. So default route thru primary link will be preferred than secondary link.
 
Inbound traffic on CPE
All inbound traffic will come in thru primary line (12.1.3.1) due to secondary link tagged local-pref 80 thru BGP community string that was provided by ISP.

 
 

[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 weight 1000
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 send-community
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 outbound out
!
ip classless
!
ip as-path access-list 10 permit ^$
!
route-map outbound permit 10
set community 20:80
!
!
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
neighbor 12.1.3.1 route-map customer in
!
ip community-list 1 permit 20:1
ip community-list 2 permit 20:2
ip community-list 3 permit 20:3
ip community-list 4 permit 20:80
ip community-list 4 permit 20:120
! 
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 
! 
route-map customer permit 10
 match community 1
 set as-path prepend 20
!
route-map customer permit 20
 match community 2
 set as-path prepend 20 20
!
route-map customer permit 30
 match community 3
 set as-path prepend 20 20 20
!
route-map customer permit 40
 match community 4
 set local-preference 80
!
route-map customer permit 50
 match community 5
 set local-preference 120
!
route-map customer permit 60
! 
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
neighbor 12.1.3.1 route-map customer in
!
ip classless
!
ip community-list 1 permit 20:1
ip community-list 2 permit 20:2
ip community-list 3 permit 20:3
ip community-list 4 permit 20:80
ip community-list 4 permit 20:120
! 
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 
! 
route-map customer permit 10
 match community 1
 set as-path prepend 20
!
route-map customer permit 20
 match community 2
 set as-path prepend 20 20
!
route-map customer permit 30
 match community 3
 set as-path prepend 20 20 20
!
route-map customer permit 40
 match community 4
 set local-preference 80
!
route-map customer permit 50
 match community 5
 set local-preference 120
!
route-map customer permit 60

!
line con 0
line aux 0
line vty 0 4
login
!
end 

[Verifing output] 

CPE# show ip bgp neighbors 12.1.3.2 ad
BGP table version is 6, 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 6, 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 6, 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
r> 0.0.0.0          12.1.3.2                 0          1000 20 i
*> 100.100.100.0/24 12.1.3.2                            1000 20 ?
*> 200.200.200.0    12.1.3.2                            1000 20 ?

Total number of prefixes 3
CPE#

CPE# show ip bgp neighbors 12.1.4.2 ro
BGP table version is 6, 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
r  0.0.0.0          12.1.4.2                 0             0 20 i
*  100.100.100.0/24 12.1.4.2                               0 20 ?
*  200.200.200.0    12.1.4.2                               0 20 ?

Total number of prefixes 3
CPE#
 

PE1#show ip bgp nei 12.1.3.1 ro
BGP table version is 70, 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 116, 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     80      0 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


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Author: Chris Yoon

IT professional