Configuration of BGPv4 is simple on Cisco. Here in this scenario R2 is on AS 1 and rest of the other routers i.e. R1,R5 and R3 are on AS 2.
Configuration Objective is to achieve inter AS communication. Simple BGP configuration neigbourship and broadcasting network. LANs shown as clouds C1 and C2.
Internet is connected through C2 cloud. Actually I used DSL modem located in C2 clound. And put routes into it for 192.168.56.0/24 towards R3. So that returning traffic can come in 192.168.56.0/24 network.
In C1 cloud I used VM OS to test all connectivity.
Traffic from VM OS passess through AS 1,AS 2 and to internet. Here is the trace from R2 router for e.g. gmail.com.
Version of IOS on all routers 12.4
R2#traceroute gmail.com source f0/0
Type escape sequence to abort.
Tracing the route to gmail.com (72.14.204.83)
1 172.16.1.2 [AS 2] 56 msec 24 msec 48 msec
2 10.1.1.2 [AS 2] 36 msec 44 msec 48 msec
3 10.1.1.6 [AS 2] 24 msec 48 msec 64 msec
4 * * * #DSL Hop found
5 59.95.96.1 [AS 2] 128 msec 156 msec 136 msec
6 218.248.255.90 [AS 2] 124 msec 140 msec 148 msec
7 121.244.78.166 [AS 2] 116 msec 136 msec 172 msec
8 59.163.25.242 [AS 2] 116 msec 148 msec 148 msec
9 121.240.0.18 [AS 2] 156 msec 140 msec 152 msec
10 216.239.43.214 [AS 2] 124 msec 148 msec 132 msec
11 72.14.232.93 [AS 2] [MPLS: Label 697405 Exp 4] 216 msec
72.14.232.100 [AS 2] [MPLS: Label 391761 Exp 4] 168 msec 160 msec
12 66.249.94.74 [AS 2] 228 msec
66.249.94.72 [AS 2] 200 msec
66.249.94.74 [AS 2] 252 msec
13 209.85.254.155 [AS 2] [MPLS: Label 509864 Exp 4] 500 msec
72.14.232.115 [AS 2] [MPLS: Label 416579 Exp 4] 432 msec
209.85.254.155 [AS 2] [MPLS: Label 520248 Exp 4] 464 msec
14 209.85.255.59 [AS 2] [MPLS: Label 481915 Exp 4] 464 msec 460 msec 480 msec
15 216.239.43.212 [AS 2] [MPLS: Label 729408 Exp 4] 468 msec 476 msec 448 msec
16 209.85.241.210 [AS 2] [MPLS: Label 780964 Exp 4] 448 msec
216.239.43.81 [AS 2] [MPLS: Label 715357 Exp 4] 420 msec 432 msec
17 209.85.248.222 [AS 2] 460 msec 584 msec 472 msec
18 66.249.94.54 [AS 2] 416 msec
209.85.242.209 [AS 2] [MPLS: Label 752323 Exp 4] 444 msec
209.85.248.222 [AS 2] 432 msec
19 72.14.204.83 [AS 2] 440 msec 436 msec 452 msec
and from VM OS:
C:\>tracert -d gmail.com
Tracing route to gmail.com [72.14.204.19]
over a maximum of 30 hops:
1 70 ms 17 ms 2 ms 192.168.56.2
2 35 ms 40 ms 10 ms 172.16.1.2
3 37 ms 27 ms 49 ms 10.1.1.2
4 51 ms 27 ms 19 ms 10.1.1.6
5 * * * Request timed out. #this hop is the DSL modem connected
6 151 ms 147 ms 147 ms 59.95.96.1
7 145 ms 180 ms 169 ms 218.248.255.90
8 143 ms 124 ms 130 ms 115.113.128.17
9 134 ms 126 ms 122 ms 59.163.25.242
10 223 ms 135 ms 126 ms 121.240.0.18
11 124 ms 134 ms 127 ms 216.239.43.214
12 158 ms 188 ms 174 ms 72.14.232.93
13 187 ms 189 ms 215 ms 66.249.94.74
14 498 ms 455 ms 422 ms 209.85.254.155
15 492 ms 429 ms 444 ms 209.85.255.37
16 453 ms 431 ms 433 ms 216.239.43.212
17 426 ms 431 ms 459 ms 216.239.43.81
18 446 ms 432 ms 431 ms 209.85.248.222
19 429 ms 490 ms 429 ms 209.85.242.209
20 458 ms 486 ms 433 ms 72.14.204.19
Trace complete.
First We focus on R2. This router resides in AS 1 as a whole.
Its configuration is as follow:
interface FastEthernet0/0
ip address 192.168.56.2 255.255.255.0
duplex auto
speed auto
interface Serial1/0
ip address 172.16.1.1 255.255.255.252
serial restart-delay 0
router bgp 1
no synchronization
bgp log-neighbor-changes
redistribute connected route-map allowed
neighbor 172.16.1.2 remote-as 2
no auto-summary
! Only these routes will be broadcasted
ip access-list standard allowed
permit 192.168.56.0
route-map allowed permit 10
match ip address allowed
Configuration of R1
interface Loopback0
ip address 10.81.199.1 255.255.255.255
interface Serial1/0
ip address 172.16.1.2 255.255.255.252
serial restart-delay 0
interface Serial1/2
ip address 10.1.1.1 255.255.255.252
serial restart-delay 0
! IGP for intra AS domain routing
router ospf 1
log-adjacency-changes
network 10.1.1.0 0.0.0.255 area 0
network 10.81.199.0 0.0.0.255 area 0
router bgp 2
! Will not rely on IGP for routes
no synchronization
bgp log-neighbor-changes
!Neigbor relationship
neighbor 10.81.199.2 remote-as 2
! update source will be lo0
neighbor 10.81.199.2 update-source Loopback0
!for routes to be seen from iBGP hop coming from eBGP hop
neighbor 10.81.199.2 next-hop-self
neighbor 10.81.199.3 remote-as 2
neighbor 10.81.199.3 update-source Loopback0
neighbor 10.81.199.3 next-hop-self
neighbor 172.16.1.1 remote-as 1
no auto-summary
R5 configuration:
interface Loopback0
ip address 10.81.199.3 255.255.255.255
interface Serial1/1
ip address 10.1.1.5 255.255.255.252
serial restart-delay 0
!
interface Serial1/2
ip address 10.1.1.2 255.255.255.252
serial restart-delay 0
router ospf 1
log-adjacency-changes
network 10.1.1.0 0.0.0.255 area 0
network 10.81.199.0 0.0.0.255 area 0
router bgp 2
no synchronization
bgp log-neighbor-changes
neighbor 10.81.199.1 remote-as 2
neighbor 10.81.199.1 update-source Loopback0
neighbor 10.81.199.2 remote-as 2
neighbor 10.81.199.2 update-source Loopback0
no auto-summary
!
R3 Configuration:
interface Loopback0
ip address 10.81.199.2 255.255.255.255
!
interface FastEthernet0/0
ip address dhcp
duplex auto
speed auto
interface Serial1/1
ip address 10.1.1.6 255.255.255.252
serial restart-delay 0
!
router ospf 1
log-adjacency-changes
network 10.1.1.0 0.0.0.255 area 0
network 10.81.199.0 0.0.0.255 area 0
!
router bgp 2
no synchronization
bgp log-neighbor-changes
! Default route redistributionnetwork 0.0.0.0
network 192.168.1.0
neighbor 10.81.199.1 remote-as 2
neighbor 10.81.199.1 update-source Loopback0
neighbor 10.81.199.3 remote-as 2
neighbor 10.81.199.3 update-source Loopback0
no auto-summary
!
! Default route towards DSL modem
ip route 0.0.0.0 0.0.0.0 192.168.1.1
