BGP学习 总结3

BGP DECISION PROCESS

1 largest weight ( local orininated path :32768 other 0 )

2 largest local-preefernce (BGP default local-preference )default 100

3 prefer local paths (decreasing preference :default -orininate in neighbor,default -information -orininate in global,network,redistribute,aggregated)

4 shortest as _path ('bgp bestpath as-path ignore' bypasses this step;AS_SET counts as 1 ;as_confed_sequence and as_confed_set are not counted)

5 lowest origin code (0 -igp,1-egp,2-imcomplete0

6 lowest med ('bgp always-compare-med;bgp bestpath med-confed;bgp bestpatch med missing-as-worst;bgp determinstic-med) default 0

7 ebgp prefered over ibgp (confed ,path are treated as internal paths) 8 closest IGP neighbor (best cost)

9 determine if multiple paths require installation (multipath)

10 if paths are external choose the oldest one (flap prevention ) skipped if "bgp bestpath comfare-routerid)

11 lowest router-id

12 minimum cluster-list length (RR enivronment)

13 lowest neighbor address

REGEXP  .      single character

 *      zero or more

 +      one or more

 ?      zero or one

[]        range

[^]      negate range

^        begining of input

$        end of input

_         , () {} ^ $ ,space

\         escape special character

\1       repeat a match ()

|         logical OR

PATH ARRTIBUTES

<TYPE  ,LENGTH,VALUE>

            FLAGES                                          CODE

------------------------------------------------------------------------------------

0 | 1 |2 | 3 |                    |                                               |

-------------------------------------------------------------------------------------

0---------    0 Well-Known ; 1 -Optional

1--------      0  Non-transitive ; 1 =Transitive

2---------     0 Complete; 1 =Partial

3----------     0 1bytes  ; 1=2bytes (Attr len Field)

1 origin                             WK  M

2 as_path                           WK  M

3 next_hop                         WK M

4 MED                                ON  T

5 local_pref                        WK  D

6 atomin_aggreagte            WK  D

7 aggregator                       O   T

8 community                       O   T

9 originator_id                     O NT

10 cluster_list                     

12 advertiser                       

13 rcid_path/cluster_ID         

14 mp_reachable NLRI         O NT

15 mp_unreachable NLRI      O NT

16  extended communities

Filter Sequence :

IN :

1 prefix-list

2 filter-list

3 weight

4 route-map

OUT:

1 prefix-list

2 filter-list

3 router-map

IGP:

1 distribute-list

2 route-map (redistribution)