BGP neighbor
Principle overview ：
Routing information protocol is divided into internal gateway protocol （IGP：Interior Gateway Protocol） And external gateway protocol （EGP：Exterior Gateway
Protocol） Two categories .IGP For autonomous systems AS（Autonomous
System） inside ,EGP be used for AS between . original IGP It's called GGP（Gateway-to-Gateway
Protocol） Routing protocol , And the earliest EGP It's a kind of EGP（Exterior-Gateway
protocol, be careful , It is related to class aliases EGP Same name , It has now been abolished ） Routing protocol . at present , common IGP include RIP,OSPF,IS-IS etc. , And common EGP only BGP（Border
Gateway Protocol）.
Experimental purpose ：
understand BGP Application scenarios of the protocol
understand IBGP and EBGP Concept of neighbor
to configure IBGP And EBGP Neighbor relationship
Experimental topology :
1: Basic configuration ：
Will be in R1 and R2 Use a direct physical interface to configure IBGP Neighbor relationship , To achieve link redundancy ,R1 and
R2 Two links are deployed between , When one of the links fails , Another physical link can provide connectivity .
R1: # interface GigabitEthernet0/0/0 ip address 10.0.12.1 255.255.255.0 #
interface GigabitEthernet0/0/1 ip address 10.0.21.1 255.255.255.0 # interface
GigabitEthernet0/0/2 # interface NULL0 # interface LoopBack0 ip address
10.0.1.1 255.255.255.255 # bgp 100 router-id 10.0.1.1 peer 10.0.12.2
as-number 100 peer 10.0.21.2 as-number 100 # ipv4-family unicast undo
synchronization network 10.0.1.1 255.255.255.255 peer 10.0.12.2 enable
peer 10.0.21.2 enable R2:, # interface GigabitEthernet0/0/0 ip address
10.0.12.2 255.255.255.0 # interface GigabitEthernet0/0/1 ip address 10.0.21.2
255.255.255.0 # interface GigabitEthernet0/0/2 ip address 10.0.23.2
255.255.255.0 # interface GigabitEthernet4/0/0 ip address 10.0.32.2
255.255.255.0 # interface NULL0 # interface LoopBack0 ip address 10.0.2.2
255.255.255.255 # bgp 100 router-id 10.0.2.2 peer 10.0.12.1 as-number 100
peer 10.0.12.2 as-number 100 peer 10.0.21.1 as-number 100 # ipv4-family
unicast undo synchronization peer 10.0.12.1 enable undo peer 10.0.12.2
enable peer 10.0.21.1 enable R3: # interface GigabitEthernet0/0/0 ip address
10.0.23.3 255.255.255.0 # interface GigabitEthernet0/0/1 ip address 10.0.32.3
255.255.255.0 # interface GigabitEthernet0/0/2 # interface NULL0 # interface
LoopBack0 ip address 10.0.3.3 255.255.255.255
2: to configure IBGP neighbor ：
We have finished the configuration based on the basic configuration , Next, let's look at BGP Neighbor relationship
Can see ,R2 Now there are two BGP neighbor , Use separately R1 of G0/0/0 and G0/0/1 Interface address ,AS Number is 100, And R2 own AS Same number , therefore R2 And R1 by IBGP neighbor , Current neighbor status is Established, Indicates that the neighbor relationship has been fully established .
[R1]bgp 100 [R1-bgp]network 10.0.1.1 32
After configuration , stay R2 View on BGP Routing table
In order to make R1 of Loopback 0 Interface and R2 of Loopback Interface established TCP conversation , Need in R1 and R2 Configure to arrive at the opposite party Loopback 0 Static routing of interface .
R1:Lo0 Static state of ： [R1]ip route-static 10.0.2.2 32 10.0.12.2 [R1]ip ro [R1]ip route-s
[R1]ip route-static 10.0.2.2 32 10.0.21.2 R2：Lo0 Static state of ： ip route-static 10.0.1.1
255.255.255.255 10.0.12.1 ip route-static 10.0.1.1 255.255.255.255 10.0.21.1
Delete the previous configuration with physical interface IBGP Neighbor's order , And use Loopback 0 Interface re establishment IBGP Neighbor relationship .
[R1]bgp 100 [R1-bgp]undo peer 10.0.12.2 [R1-bgp]un peer 10.0.21.2 [R1-bgp]peer
10.0.2.2 as-number 100 [R2]bgp 100 [R2-bgp]un peer 10.0.12.1 [R2-bgp]un peer
10.0.21.1 [R2-bgp]peer 10.0.1.1 as-number 100
After the above configuration is completed , stay R1 View on BGP Neighbor relationship
Can see ,R1 And R2 Our neighbors stay Active state , Not Extablished, This shows R1 And R2 It has not been established normally IBGP Neighbor relationship .
stay R1 Specify to use your own Loopback 0 Send as interface address BGP Source of message IP address ,R2 A similar command is required on
[R1]bgp 100 [R1-bgp]peer 10.0.2.2 connect-interface lo 0 [R2]bgp 100
[R2-bgp]peer 10.0.1.1 connect-interface lo 0
After the above configuration is completed , stay R2 View on BGP Routing table
Can see ,R2 of BGP There is only one destination in the routing table 10.0.1.1/32 Routing , Next jump is 10.0.1.1
View again R2 of IP Routing table
to configure EBGP neighbor
stay R2 and R3 Use on Loopback 0 Interface to establish EBGP Neighbor relationship
[R2]bgp 100 [R2-bgp]peer 10.0.3.3 as-number 200 [R3]bgp 200 [R3-bgp]router-id
10.0.3.3 [R3-bgp]peer 10.0.2.2 as-number 100
After the above configuration is completed , stay R3 View on BGP Neighbor relationship
Can see ,R2 And R3 Your neighbor status has been stuck in IdIe state , It indicates that the neighbor relationship has not been established normally .
We know ,BGP The precondition of establishing neighbor relationship is to be able to establish TCP conversation , And now R2 and R3 It doesn't exist in the world. Go to each other Loopback 0
Interface routing , Therefore, it cannot be established TCP conversation , To solve this problem , Can be in R2 and R3 Configuration arrival on Loopback 0 Static routing of interface .
[R2]ip route-static 10.0.3.0 24 10.0.23.3 [R2]ip route-static 10.0.3.0 24
10.0.32.3 [R3]ip route-static 10.0.2.0 24 10.0.23.2 [R3]ip route-static
10.0.2.0 24 10.0.32.2
After the above configuration is completed , stay R3 View on BGP Neighbor relationship
Can see ,R2 And R3 The relationship between neighbors has been stuck in Active state , It shows that the neighbor relationship has not been established normally
[R2-bgp]peer 10.0.3.3 connect-interface lo 0 [R3-bgp]peer 10.0.2.2
connect-interface lo 0
After configuration , stay R3 View on BGP Neighbor relationship
By default ,EBGP Sending between neighbors BGP Message time ,TTL by 1, therefore EBGP By default, neighbors must be physically connected . But when R2 and R3 use Loopback 0
When establishing neighbor relationship with interface , Because the physical direct connection interface is not used , therefore TTL Will be subtracted more than once , become 0, Eventually BGP The message will be discarded ; As a result, the neighbor relationship cannot be established , To solve this problem , Can be modified EBGP Sent by neighbors BGP Message TTL value , Make the message TTL Value greater than 1
stay R2 and R3 Upper configuration BGP Message TTL Value is 2
[R2-bgp]peer 10.0.3.3 ebgp-max-hop 2 [R3-bgp]peer 10.0.2.2 ebgp-max-hop 2
After the above configuration is completed , stay R3 View on BGP Neighbor relationship
Can see ,R2 And R3 Has been established between EBGP Neighbor relationship
It should be noted that , In the actual scene , Commonly used Loopback Interface to establish IBGP Neighbor relationship , Use physical interfaces to establish EBGP Neighbor relationship .
remarks ： If there is an error , Please understand !
This article is my study note , For reference only ! If repeated !!! Please contact me !
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