[hcip] BGP features

BGP  The characteristics are divided into 「 It is generally acknowledged that we must comply with the law 」「 Recognize any attribute 」「 Optional properties 」「 Optional non transition attribute 」

It is generally acknowledged that we must comply with the law ： all BGP  All devices can recognize such attributes and must exist in Update  In the message

Recognize any attribute ： all BGP  Devices can recognize such attributes and may not exist in Update  In the message

Optional properties ： Vendor private property ,BGP  The device may not recognize such attributes , But will still receive forwarding

Optional non transition attribute ： Vendor private property ,BGP  The device may not recognize such attributes , If it is not recognized, it will be ignored and not forwarded

（1） Protocol preferences （PrefVal）

Huawei BGP  Private property ; Local validity is not passed to any BGP  neighbor ; The default is 0; The bigger the better

When you don't want to affect the routing of other devices , Protocol preferences can be used

preferred-value

（2） Local priority （Local_Pref）

Recognize any attribute ; Only in one AS  Internal delivery ; Default 100, The bigger the better

Apply to AS  When there are multiple exits in memory

local-preference「 priority 」： Modify the local priority of the route 
default local-preference： Modify the default local priority 

（3） Prefer locally generated routes

Jump for now 127.0.0.0  or 0.0.0.0  when , That is, generate a route locally

Local routing priority ： Manual aggregation > Automatic aggregation > network > import >  Routes learned from peers

（4） optimization AS_Path  The shortest route

It is generally acknowledged that we must comply with the law

as_path「AS Number 」add： increase AS list 
as_path「AS Number 」overwrite： With the new AS The list overwrites the original AS list 
as_path「AS Number 」none overwrite： Delete old AS list 
bestroute as-path-ignore： Ignore as_path Path properties 

（5） Compare Origin  attribute （ Origin attribute ）

In turn, it is preferable to Origin  The type is ：IGP > EGP > Incomplete

i（IGP）：network

e（EGP）： It shows that it is from EGP  Protocol learned routing

？（Incomplete）：import-route

（6） optimization MED  Lowest route

BGP  Of Cost; Optional non transition attribute ; The smaller the better ; If the message does not carry MED The default is 0

By default , There are only two. BGP  route  as_path  On the far left of AS  Only when the number is the same MED Compare

MED =  Turn into BGP  Before routing Cost  value

IBGP → EBGP,EBGP → EBGP： Do not carry MED

IBGP → IBGP,EBGP → IBGP： Carry carry MED

compare-defference-as-med： Allow to compare different as The no. med value 
diterministic-med： Give priority to the leftmost AS Number 

（7）EBGP > IBGP

（8）  Next jump  metric  Small routing

（9） Load sharing , Need to be AS_Path Same and manually opened

AS_Path  identical ：AS  Same number ;AS  The same number ;AS  Same order

Whether the load is turned on or not ,BGP  Devices will choose the best route to pass to their neighbors  

maximum load-balancing ？
integer： in the light of ibgp and ebgp Route on load 
ibgp： in the light of ibgp Route on load 
ebgp： in the light of ebgp Route on load 

load-balancing as-path-ignore： Load sharing is not compared as_path attribute