BGP学习 总结1

BGP

 

TIMERS:

          timers bgp <keepalive><holdtime>

          neighbor <ip> timers <keepalive><holdtime>

          bgp scan-time <scanner-interval>

         

          neighbor <ip>advertistment-interval <sec>

          updates are rate limited,5 sec -IBGP,30sec -EBGP.

 

FEATURES:

          tcp/179

          keeplive every 60 sec(19 bytes header);holdtime 180 sec

          header:16 bits marker--- all 1s if no auth.2 bits length ,1 bit type

          message :open , keepalive, update,notification

 

          BGP has own internal queue 100 packets ,it cannot be change;

          It is not the same queue  as HOLD-queue 100 in

 

SESSION:

         if ebgp-multishop is used ,there must be a specific route to remote peer ,

         default will not work ,although you can ping

 

         neighbor <ip>ebgp-multihop[<ttl >]

         by default ttl for ebgp session is 1

     

         neighbor <ip>disable-connected-check

         can be used for directly connected ebgp peers

 

          neighbor<ip >update-source<if>

          for not directly connected session outgoing intearface must be set (with ip defind as a neighbor on remote peer)

 

         neighbor<ip >maximum-prefix<max >

          [<threshold%>][warning-only][restart sec ]

 

FSM:

         idle ---the router sets the connectretry timer (60sec) and

                    cannot attempt to restart BGP until the timer expires

          connect---the bgp process is waiting for the tcp connection to be completed

          open-sent------open message has been sent,and bgp is waiting to hear open from message

          open-confirm-------the bgp process waits for a keeplive or notification message

          active---------the bgp process is trying to initiate a tcp connection with the neighbor

          established

 

MTU:

          tcp path mtu discovery is enabled by default for all bgp  neighbor session

          ip tcp path-mtu-discovery

          every 10 min trial-erroy ,affects session originated by router

 

          neigbor<ip >transport path-mtu-discovery

          MSS 576 by default (536 without TCP/IP headers)

          windows is 16K (always ,regardless of CLI configuration)

 

SYCHRONIZATION:

         if   ospf is used as IGP then OSPF RID and BGP RID advertising the same prefix mtst be the same

         do not consider ibgp route in bgp table as sets unless the exact prefix was learned via IGP and is currently in roueting table

 

 SECURITY:

           MD5 authentication  

           neigbbor<ip>password<string >

 

           TTL check

           both sides must configure this feature 

            neighbor <ip>ttl-security hops<#> 

           does not prevent attacks from the same segment ot distance

 

PEER_GROUP:

           Single bgp scan in performed for a leader (lowest ip)
only,and replicated to other members.

            IBGP and EBGP cannot be int the same peer-group

           clear ip bgp update-group<index-group>

           show ip bgp update-group [summary]

            show ip bgp replication

 

LOAD-BALANCING

             maximum-path [ibgp]<up-to-6>

             neibhbor <ip>ebgp-multihop <ttl >