笔记丶TCPIPVolume2-BGP-20101213

Load balancing works with eBGP (not iBGP)

BGP Message Types
    Open \ Keepalive \ Update \ Notification
after BGP session established -- TCP 179    send open messages

Open --
    BGP version number  (2,3,4) default 4 ,use 'neighbor version' change  (earlier versions reject BGP-4,BGP-4 can send earlier version open messages).
    Autonomous system number  determine eBGP or iBGP.
    Hold time  0 or at least 3 ,default 180s .If the neighbors' hold times differ,the smaller of the two times becomes the accepted hold time.
    BGP identifier
    Optional parameters   authentication,multiprotocol support,route refresh.

Keepalive Message --
    If a router accepts the parameters specified in its neighbor's Open message,it responds with a Keepalive.
    Subsequent Keepalives are sent every 60s default,or a period equal to one-third the agreed-upon hold time.

Update Message -- advertise feasible routes,withdrawn routes,or both.
    Network Layer Reachability Information (NLRI)  lengths and IP address prefixes.
    Path Attributes   use to choose a shortest path,detect routing loops,and determine routing policy.
    Withdrawn Routes   lengths and ip address prefixes.

Notification Message --
    When an error is detected , send the Notification messages.

 

The BGP finite state machine

Idle--Connect State--Active State--OpenSent State--OpenConfirm State--Established State

 

Path Attributes
    Well-known mandatory
         ORIGIN
         AS_PATH
         NEXT_HOP
    Well-known discretionary
         LOCAL_PREF
         ATOMIC_AGGREGATE
    Optional transitive
         AGGREGATOR
         COMMUNITY
    Optional nontransitive
         MULTI_EXIT_DISC
         ORIGINATOR_ID
         CLUSTER_LIST