BGP Backdoor
EBGP Ad is 20, OSPF 110
R1, R2 - one customer with ospf route
R3 - ISP - provides bgp route
By default bgp route will win with lower ad
Before 2.2.2.2 via BGP
show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
+ - replicated route, % - next hop override
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
B 2.2.2.2 [20/0] via 192.168.13.3, 00:01:11
192.168.12.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.12.0/24 is directly connected, FastEthernet0/0
L 192.168.12.1/32 is directly connected, FastEthernet0/0
192.168.13.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.13.0/24 is directly connected, FastEthernet1/0
L 192.168.13.1/32 is directly connected, FastEthernet1/0
R1#
R1#show ip bgp
BGP table version is 3, 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, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 0.0.0.0 0 32768 i
*> 2.2.2.2/32 192.168.13.3 0 3 2 i
After
- backdoor
router bgp R1(config-router)#network 1.1.1.1 mask 255.255.255.255 backdoor R2(config-router)#network 2.2.2.2 mask 255.255.255.255 backdoor``` R1#show ip route Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, * - candidate default, U - per-user static route o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP + - replicated route, % - next hop override
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets C 1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets O 2.2.2.2 [110/2] via 192.168.12.2, 00:00:03, FastEthernet0/0
192.168.12.0/24 is variably subnetted, 2 subnets, 2 masks C 192.168.12.0/24 is directly connected, FastEthernet0/0 L 192.168.12.1/32 is directly connected, FastEthernet0/0
192.168.13.0/24 is variably subnetted, 2 subnets, 2 masks C 192.168.13.0/24 is directly connected, FastEthernet1/0 L 192.168.13.1/32 is directly connected, FastEthernet1/0 R1# R1#show ip bgp BGP table version is 1, 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, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed, Origin codes: i - IGP, e - EGP, ? - incomplete RPKI validation codes: V valid, I invalid, N Not found
Network Next Hop Metric LocPrf Weight Path * 2.2.2.2/32 192.168.13.3 0 3 2 i R1# ``` ## **Config** **R1** ``` interface Loopback0 ip address 1.1.1.1 255.255.255.255 ! interface FastEthernet0/0 ip address 192.168.12.1 255.255.255.0 ! interface FastEthernet1/0 ip address 192.168.13.1 255.255.255.0 ! router ospf 1 network 1.1.1.1 0.0.0.0 area 0 network 192.168.12.0 0.0.0.255 area 0 ! router bgp 1 bgp log-neighbor-changes network 1.1.1.1 mask 255.255.255.255 backdoor neighbor 192.168.13.3 remote-as 3 ``` **R2** ``` interface Loopback0 ip address 2.2.2.2 255.255.255.255 ! interface FastEthernet0/0 ip address 192.168.12.2 255.255.255.0 ! interface FastEthernet1/0 ip address 192.168.23.2 255.255.255.0 ! router ospf 1 network 2.2.2.2 0.0.0.0 area 0 network 192.168.12.0 0.0.0.255 area 0 ! router bgp 2 bgp log-neighbor-changes network 2.2.2.2 mask 255.255.255.255 backdoor neighbor 192.168.23.3 remote-as 3 ``` **R3** ``` interface FastEthernet0/0 ip address 192.168.23.3 255.255.255.0 ! interface FastEthernet1/0 ip address 192.168.13.3 255.255.255.0 ! router bgp 3 bgp log-neighbor-changes neighbor 192.168.13.1 remote-as 1 neighbor 192.168.23.2 remote-as 2 ```