[hcip] BGP Foundation

Catalog

One 、GBP  Message type

Two 、BGP  State machine

3、 ... and 、GBP  Neighborhood building

Four 、BGP  Routing notification principles

5、 ... and 、 Routing black holes

---

One 、GBP  Message type

GBP  Message type ：open（ negotiation BGP  Parameters ）,update（ Exchange routing information ）,keepalive（ Keep the neighborhood ）,notification（ Notice of error ）,route-refresh（ It is used to re request routing information from peers after changing the routing policy ）

Two 、BGP  State machine

（1）Idle, The initial state , Only experience Start  After the event , That is to say 32  Seconds later , Will start building neighbors

（2）Connect,GBP  Start the connection retransmission timer （32  second ）, wait for TCP  Connection complete . Successful connection , entering OpenSent  state ; The connection fails , entering Active  state ; Timer timeout , Then stay in this state and try to establish a relationship with other peers

（3）Active, If the neighbor is established successfully , entering OpenSent, If it fails , Stay in this state , If the timer times out and no response is received , go back to Connect

（4）OpenSent, If you receive Open  correct , Then send Keepalive  Message enters OpenConfirm, If wrong , Then send Notification  message , go back to Idle  state .Open  Key message contents ：My AS（ Identify yourself AS  Area ）,Hold Time（ Default 180  second , If both parties disagree, use the small ）,Router ID（ Oneself RID）.Open  The message carries 3  Negotiation ability ：IPV4  Unicast routing function , Route refresh function ,4  byte AS  No. 1 support capability ; The address cluster must have a successful negotiation .

（5）OpenConfirm, In this state ,BGP  Waiting for a response , If received Keepalive  message , entering Established  state , If received Notification  message , Then go back to Idle  state

（6）Established, In this state , If you receive an error message , Then go back to Idle  state

3、 ... and 、GBP  Neighborhood building

Default build IBGP  Neighbor time ,TTL = 255; Default build EBGP  Neighbor time ,TTL = 1

establish IBGP  When neighbors use loopback, it is to be more stable

BGP  Neighbors are divided into 「IBGP  neighbor 」 and 「EBGP  neighbor 」

IBGP  neighbor ： Neighbors and themselves AS  Same number

EBGP  neighbor ： Neighbors and themselves AS  Different numbers

Four 、BGP  Routing notification principles

（1）BGP  Only the best route among the effective routes will be announced ;（*>）,*  Means effective ,>  Represents the best

（2） self-generated BGP  Route notifications to all BGP  neighbor

（3） from IBGP  Routes received by neighbors , Will pass to EBGP  neighbor , It will not be passed on to IBGP  neighbor （ Guard ring ）

（4） from EBGP  Routes received by neighbors , Will be passed to all BGP neighbor

（5）BGP  Send a route to  EBGP  Carry yourself AS  Number , After the other party receives it, check whether it contains itself AS  Number , If included, indicate that you have received , Do not receive , If not, receive

（6） from EBGP  Send to IBGP  The next hop of the route will not be automatically modified

5、 ... and 、 Routing black holes

  Routing black holes can be used BGP  Synchronize to solve ,BGP  Sync ： from IBGP  The route received by the neighbor needs to be in itself IGP  Presence in table , To participate in the election of the best route .

because BGP  Synchronization cannot completely solve the problem of routing black holes , So you can use the following methods ： Use full interconnection 、 establish GRE  Tunnel 、 establish LSP  Tunnel

GRE  Tunnel ： Add the source item to the header of the data frame IP

gbp「 Process number 」
peer「 neighbor IP」as-number「AS Number 」
peer「 neighbor IP」connect-interface「 port 」
refresh bgp all export： Resend the routing information to all BGP neighbor 
refresh bgp all import： All requests BGP Neighbors resend routing information to themselves 
peer「IP」next-hop-local： Modify the next hop when announcing the route , Just configure the equipment at the boundary 
undo synchronization： close BGP sync （ Off by default ）

gre Tunnel ：
interface tunnel 0/0/1
tunnel protocol gre
source「 Source 」
destination「 Objective 」
ip add「IP」