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BGP Lab 1


Study lab for ebgp and ibgp. 
Figure 1.1
In this scenario ebgp and ibgp configured.

Router 1 and router 2 connect as eBGP. Router 1 and router 3 connect as iBGP.

R2
router bgp 100
neighbor 10.1.12.1 remote 200

R1 
router bgp 200
neighbor 10.1.12.2 remote 100
neighbor 10.1.13.3 remote 200

R3
router bgp 200
neighbor 10.1.13.1 remote 200


Now neighbor is up we can verify neighbors with 'show ip bgp summary'.

R2#show ip bgp summary
BGP router identifier 2.2.2.2, local AS number 100
BGP table version is 7, main routing table version 7
2 network entries using 234 bytes of memory
2 path entries using 104 bytes of memory
3/2 BGP path/bestpath attribute entries using 372 bytes of memory
1 BGP AS-PATH entries using 24 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 734 total bytes of memory
BGP activity 4/2 prefixes, 4/2 paths, scan interval 60 secs

Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
10.1.12.1       4   200       5       5                   7      0    0     00:00:05        1

Verify the routing tables.

R1
R1#show ip route bgp
     2.0.0.0/24 is subnetted, 1 subnets
B       2.2.2.0 [20/0] via 10.1.12.2, 00:25:33
     3.0.0.0/24 is subnetted, 1 subnets
B       3.3.3.0 [200/0] via 10.1.13.3, 00:30:02

R2
R2#show ip route bgp
     3.0.0.0/24 is subnetted, 1 subnets
B       3.3.3.0 [20/0] via 10.1.12.1, 00:24:44

R3
R3#show ip route
     3.0.0.0/24 is subnetted, 1 subnets
C       3.3.3.0 is directly connected, Loopback0
     10.0.0.0/24 is subnetted, 1 subnets
C       10.1.13.0 is directly connected, FastEthernet0/0

At router 1 and 2 can see the 3.3.3.0/24 and 2.2.2.0/24 networks but router can't see the 2.2.2.0/24 network. So we check with another way.

show ip bgp 
This command to check bgp network are best route or fail.

R3#show ip bgp
BGP table version is 2, 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
* i2.2.2.0/24       10.1.12.2                0    100      0 100 i
*> 3.3.3.0/24       0.0.0.0                  0         32768 i

2.2.20/24 is valid but not best, it next hop router is R2. R3 don't know R2 so we must change in R1 as next hop router. 
Next hop self concept is like, if you want to go U.S from Myanmar, you need to go air port.
In this scenario R1 is like air port.
 
R1 
router bgp 200
neighbor 10.1.13.3 next-hop-self

Now we see the change at next hop router.

R3#sh ip bgp
BGP table version is 3, 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
*>i2.2.2.0/24       10.1.13.1                0    100      0 100 i
*> 3.3.3.0/24       0.0.0.0                  0         32768 i

R3#sh ip route bgp
     2.0.0.0/24 is subnetted, 1 subnets
B       2.2.2.0 [200/0] via 10.1.13.1, 00:14:33

Testing
R3#ping 2.2.2.2 source 3.3.3.3

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
Packet sent with a source address of 3.3.3.3
!!!!!

R3#traceroute 2.2.2.2 source 3.3.3.3

Type escape sequence to abort.
Tracing the route to 2.2.2.2

  1 10.1.13.1 24 msec 40 msec 52 msec
  2 10.1.12.2 68 msec 72 msec 80 msec


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