BGP ---- border gateway routing protocol ----- basic experiment

BGP: Border gateway routing protocol — Dynamic routing protocol
No category Path vector EGP agreement ;

AS– Autonomous systems – Standard No 16 position 0-65535 among 1-64511 public 64512-65535 private
Expand AS Number 32 Bit binary
IGP Agreement pursuit ：1、 acyclic （ Lu Jia Xuan ） 2、 Fast convergence 3、 Less occupied resources
EGP The pursuit of agreement :
1. Controllable （ Administrators can facilitate policy interference and routing ）
2、 reliability （BGP Protocol devices need to interact with a large number of routing entries , However, periodic update cannot be selected to occupy link resources , Therefore, only trigger updates can be performed ; And BGP In order to save cost in the agreement working environment , There must be indirect connections, and it is necessary to establish neighbor relations — Unicast neighbors ）— be based on TCP Work - Three handshakes, four disconnects 4 A reliable transmission mechanism – TCP Can only work based on unicast
unicast — need IP Can be up to — rely on IGP BGP Carried on IGP above
3、AS-BY-AS With a AS For a jump ;

Two 、BGP characteristic ：
1） Classless path vector ----- Upgraded version of distance vector —AS–BY–AS
2） Use unicast updates to send all information ; be based on TCP 179 Port operation
3） Incremental updating – Trigger only aperiodic
4） Have rich attributes to replace IGP Route selection based on measurement ---- Multiple parameter control protocol
5） You can implement a strong strategy for traffic in and out – Controllability
6） The default is not used for load balancing ----- Only one optimal path is generated through various routing rules
7）BGP Support authentication and aggregation （ Summary ）

3、 ... and 、BGP Data packets
Open Only responsible for the establishment of neighborhood relations , Normal receiving and sending can be done once ; carry route-id;
Keeplive Keep alive cycle 1min Query whether the neighbor relationship exists ; Actually keep alive TCP conversation ;hold time Default 3min
Update Carry routing entries Target network number + Various attributes
Notification Send and receive error data ;

Four 、BGP Working process of
1、 be based on IGP Realization IP Can be up to ;
2、 Unicast transmission between neighbors , Establish... By shaking hands three times TCP Session channel
3、 Use open The message establishes the neighbor relationship , Generally, you can send and receive once ; Generate neighbor table ;
4、 Use update Share routing information , The information carries the target network number + Various attributes
5、 Generate BGP surface — Load all routing information sent and received locally
6、 After the BGP The optimal path in the table is loaded in the routing table ;
7、 After convergence , only keeplive Keep the cycle alive
8、 all BGP All packets are based on TCP Session to ensure the reliability of transmission
9、 If an error message appears , Will use Notification Alarm
10、 Structural mutation , Use update Trigger the update

The experimental requirements ：

The topology ：

First step ：
Configure interface loopback IP Address ：

[r1]int g0/0/0
[r1-GigabitEthernet0/0/0]ip add 12.1.1.1 24
[r1-GigabitEthernet0/0/0]int g0/0/1
[r1-GigabitEthernet0/0/1]ip add 192.168.1.254 24
[r1]int l0
[r1-LoopBack0]ip add 1.1.1.1 24

[r2]int g0/0/0
[r2-GigabitEthernet0/0/0]ip add 12.1.1.2 24
[r2-GigabitEthernet0/0/0]int g0/0/1
[r2-GigabitEthernet0/0/1]ip add 23.1.1.1 24
[r2-GigabitEthernet0/0/1]int g0/0/2
[r2-GigabitEthernet0/0/2]ip add 192.168.2.254 24
[r2]int l0
[r2-LoopBack0]ip add 2.2.2.2 24

R3:
GigabitEthernet0/0/0              23.1.1.2/24    
GigabitEthernet0/0/1              34.1.1.1/24     
GigabitEthernet0/0/2              192.168.3.254/24     
LoopBack0                         3.3.3.3/24  

R4:
GigabitEthernet0/0/0              34.1.1.2/24  
GigabitEthernet0/0/1              45.1.1.1/24   
GigabitEthernet0/0/2              192.168.4.254/24     
GigabitEthernet4/0/0              54.1.1.2/24        
LoopBack0                         4.4.4.4/24    
  
R5
GigabitEthernet0/0/0              45.1.1.2/24          up         up        
GigabitEthernet0/0/1              192.168.5.254/24     up         up        
GigabitEthernet0/0/2              54.1.1.1/24          up         up       

test ：
stay R1 On pingR2, The rest remains the same .

The second step ：
At every AS Internal operation ospf agreement ,AS Interface between BGP, Cannot announce ospf in .

[r2]ospf 1 router-id 2.2.2.2
[r2-ospf-1]area 0
[r2-ospf-1-area-0.0.0.0]net 23.1.1.1 0.0.0.0
[r2-ospf-1-area-0.0.0.0]net 192.168.2.0 0.0.0.255
[r2-ospf-1-area-0.0.0.0]net 2.2.2.2 0.0.0.0

[r3]ospf 1 router-id 3.3.3.3
[r3-ospf-1]area 0
[r3-ospf-1-area-0.0.0.0]net 23.1.1.2 0.0.0.0
[r3-ospf-1-area-0.0.0.0]network 34.1.1.1 0.0.0.0 
[r3-ospf-1-area-0.0.0.0]network 192.168.3.0 0.0.0.255
[r3-ospf-1-area-0.0.0.0]net 3.3.3.3 0.0.0.0

[r4]ospf 1 rou	
[r4]ospf 1 router-id 4.4.4.4
[r4-ospf-1]area 0
[r4-ospf-1-area-0.0.0.0]net  192.168.4.0 0.0.0.255
[r4-ospf-1-area-0.0.0.0]net 4.4.4.4 0.0.0.0
[r4-ospf-1-area-0.0.0.0]net 34.1.1.2 0.0.0.0

AS1 And AS2 Used between BGP：
[r1]bgp 1
[r1-bgp]router-id 1.1.1.1
[r1-bgp]peer 12.1.1.2 as-number 2

[r2]bgp 2
[r2-bgp]router-id 2.2.2.2
[r2-bgp]peer 12.1.1.1 as-number 1
	
[r3] bgp 2
[r3-bgp]peer 4.4.4.4 as-number 2
[r3-bgp]peer 4.4.4.4 connect-interface LoopBack 0
[r3-bgp]peer 2.2.2.2 as-number 2
[r3-bgp]peer 2.2.2.2 connect-interface LoopBack 0

[r4]bgp 2
[r4-bgp]peer 3.3.3.3 as-number 2
[r4-bgp]peer 3.3.3.3 connect-interface LoopBack 0
[r4-bgp]peer 5.5.5.5 as-number 3
[r4-bgp]peer 5.5.5.5 connect-interface LoopBack 0

[r5-LoopBack0]bgp 3
[r5-bgp]peer 4.4.4.4 as-number 2
[r5-bgp]peer 4.4.4.4 connect-interface LoopBack 0

R5:

R4:

R3:

R2:

R1:

The third step ： stay R1 On the use of BGP Announce your user network segment

[r1]bgp 1
[r1-bgp]network 1.1.1.0 24

R1 Upper BGP route

see R2:

see R3 when , We found that ,r3 The route on is not optimal .
We modify R2 To R3 The next one
[r2-bgp]peer 3.3.3.3 next-hop-local
After the modification is completed , We found that R3 Become the best ,

But it cannot be transmitted to R4, because R4 Upper horizontal segmentation mechanism , So we let R2 And R4 Building neighborhoods between

[r2]bgp 2
[r2-bgp]peer 4.4.4.4 as-number 2
[r2-bgp]peer 4.4.4.4 connect-interface LoopBack 0
[r2-bgp]peer 4.4.4.4 next-hop-local

[r4]bgp 2
[r4-bgp]peer 2.2.2.2 as-number 2
[r4-bgp]peer 2.2.2.2 connect-interface LoopBack 0

R5 Ibid , because R2,R3,R4 The relevant configuration has been completed on , Just announce the network segment directly .

test ：