Wednesday, May 4, 2011

BGP: Multihomed Customer to Single ISP in Primary-Backup Setup with Static Routes

Scenario:
Multihomed customer connected to a single service provider on multiple permanent links;
Customer network using OSPF; provider network using BGP; CE-PE via static routing;
Floating static routes configured as backup on both CE and PE;

Floating Static Routes in BGP:
Once active, the floating static routes will be permanently installed in BGP; static routes are locally sourced which is preferred;
  • admin distance cannot be used in route-maps; hence, use communities
  • tag floating static routes; tags mapped to specific communities;
  • use route maps to modify the weight and/or local preference;
  • default weight: 32768

Sample ISP Route-Community Mapping:
ISP (AS 123) Service Offerings
Advertise CU RoutesPrimary?Route TagCommunityLocalPref
NoYes1000no-export 123:31000100
NoNo1010no-export 123:3100050
YesYes1001123:31000100
YesNo1011123:3100050

Customers Configurations:
CE1 Config (Primary link):
ip route 0.0.0.0 0.0.0.0 Serial0
!
router ospf 1
 default-information originate
!
CE2 Config (Backup link):
ip route 0.0.0.0 0.0.0.0 Serial0 250
!
router ospf 1
 default-information originate
!

Provider Configurations:
PE1 Config (Primary link):
ip route 11.2.3.0 255.255.255.0 serial 0 tag 1000
!
router bgp 123
 redistribute static route-map INTOBGP
!
PE2 Config (Backup link):
ip route 11.2.3.0 255.255.255.0 serial 0/0 tag 1010 250
!
router bgp 123
 redistribute static route-map INTOBGP
!

Common Route-Map Configurations on both PE1 and PE2:
route-map INTOBGP permit 10
 match tag 1000
 set community no-export 123:31000
 set local-preference 100
!
route-map INTOBGP permit 20
 match tag 1001
 set community 123:31000
 set local-preference 100
!
route-map INTOBGP permit 30
 match tag 1010
 set community no-export 123:31000
 set local-preference 50
 set weight 0
!
route-map INTOBGP permit 40
 match tag 1011
 set community 123:31000
 set local-preference 50
 set weight 0
!

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