scenario : Let's say Enterprise-1 is connecting to ISP-1 using dual homed design. There are two link which connect to the same ISP. Both link are always alive acting redundancies for each other.
Internal Routers of Enterprise-1, like IE-1 are connecting to their border router E1. In this case i'm using static routes inside the enterprise. If i use other dynamic route like OSPF or etc.., i have to configure "route redistributing" at E1.
And use a loopback interface as update source, and configure eBGP multihop with a dual BGP peer, which reduce the amount of overhead, while giving the same higher availability.
This is the Routing Table of Enterprise Router I-E1.
I-E1#sh ip route
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
i - IS-IS, 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
Gateway of last resort is 192.168.100.2 to network 0.0.0.0
192.168.100.0/30 is subnetted, 1 subnets
C 192.168.100.0 is directly connected, FastEthernet0/0
S* 0.0.0.0/0 [1/0] via 192.168.100.2 !! Default Static Route to E1
What I’m trying to do here is just try to set a default route, which saying that any packets which coming to I-E1 will go out to inner interface of Border Enterprise Router E1. Let’s say a packet come in, which want to go to ISP router ISP-1 that I-E1 don’t know. Then I-E1 will send all these into 192.168.100.2 of E1. From here, E1 will take care the rest of its journey by using its Routing table. Here is E1 routing table.
E1#sh ip route
Gateway of last resort is 0.0.0.0 to network 0.0.0.0
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
S 2.2.2.2 [1/0] via 192.168.1.2 !! This is the static route to use loopback interface.
[1/0] via 10.1.1.2
S 192.168.99.0/24 [1/0] via 192.168.100.1
C 10.0.0.0/8 is directly connected, FastEthernet2/0
C 192.168.1.0/24 is directly connected, FastEthernet1/0
192.168.100.0/30 is subnetted, 1 subnets
C 192.168.100.0 is directly connected, FastEthernet6/0
S* 0.0.0.0/0 is directly connected, Loopback0 !! This is default static route all packet via loopback
And, I tried to inject 192.168.100/24 and 192.168.99.0/24, which are internal subnets of Enterprise to advertise out in BGP message of E1. So ISP-1 will receive the route and know how to reach inner subnets or Enterprise.
ISP-1#sh ip route
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
i - IS-IS, 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
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
S 1.1.1.1 [1/0] via 192.168.1.1
[1/0] via 10.1.1.1
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected, Loopback0
B 192.168.99.0/24 [20/0] via 1.1.1.1, 00:03:28
C 10.0.0.0/8 is directly connected, FastEthernet2/0
C 192.168.1.0/24 is directly connected, FastEthernet1/0
B 192.168.100.0/24 [20/0] via 1.1.1.1, 00:03:28
ISP-1#ping 192.168.100.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.100.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 64/94/140 ms
I-E1#ping 2.2.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 172/240/300 ms
