BGP选路原则彻底理解！（下）
2011-04-27 19:55
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依次选择从EBGP、联盟、IBGP学来的路由配置修改下，R2R4 AS65002 ，R3 65003[R1]dis cu conf bgp#bgp 100 network 1.1.1.1 255.255.255.255 undo synchronization peer 12.12.12.2 as-number 200 peer 13.13.13.3 as-number 200#Return[R2-bgp]dis th#bgp 65002 confederation id 200 confederation peer-as 65003 network 2.2.2.2 255.255.255.255 undo synchronization peer 12.12.12.1 as-number 100 peer 4.4.4.4 as-number 65002 peer 4.4.4.4 next-hop-local peer 4.4.4.4 connect-interface LoopBack0#Return[R3-bgp]dis th#bgp 65003 confederation id 200 confederation peer-as 65002 network 3.3.3.3 255.255.255.255 undo synchronization peer 4.4.4.4 as-number 65002 peer 13.13.13.1 as-number 100 peer 4.4.4.4 next-hop-local peer 4.4.4.4 connect-interface LoopBack0#Return
[R4]dis cu conf bgp#bgp 65002 confederation id 200 confederation peer-as 65003 network 4.4.4.4 255.255.255.255 undo synchronization peer 2.2.2.2 as-number 65002 peer 3.3.3.3 as-number 65003 peer 2.2.2.2 connect-interface LoopBack0 peer 3.3.3.3 connect-interface LoopBack0#Return查看r2r4的bgp路由表[R4]dis bgp routing-table Total Number of Routes: 5 BGP Local router ID is 4.4.4.4 Status codes: * - valid, > - best, d - damped, h - history, i - internal, s - suppressed, S - Stale Origin : i - IGP, e - EGP, ? - incomplete Network NextHop MED LocPrf PrefVal Path/Ogn *>i 1.1.1.1/32 3.3.3.3 0 100 0 (65003) 100i * i 2.2.2.2 0 100 0 100i i 2.2.2.2/32 2.2.2.2 0 100 0 i i 3.3.3.3/32 3.3.3.3 0 100 0 (65003)i *> 4.4.4.4/32 0.0.0.0 0 0 i[R2-bgp]dis bgp routing-table Total Number of Routes: 4 BGP Local router ID is 2.2.2.2 Status codes: * - valid, > - best, d - damped, h - history, i - internal, s - suppressed, S - Stale Origin : i - IGP, e - EGP, ? - incomplete Network NextHop MED LocPrf PrefVal Path/Ogn *> 1.1.1.1/32 12.12.12.1 0 0 100i * i 3.3.3.3 0 100 0 (65003) 100i *> 2.2.2.2/32 0.0.0.0 0 0 i i 4.4.4.4/32 4.4.4.4 0 100 0 i上述现象可知ebgp>联盟>ibgp优选CLUSTER_LIST长度最短的路由；优选ORIGINATOR_ID最小的路由；这两条原则我本想还用原来的拓扑来演示，可是遗憾没找到解决方法，重新画了一个，大家将就看
R2R3R4做反射基本配置：[R1-bgp]dis th#bgp 100 router-id 1.1.1.1 dampening network 1.1.1.1 255.255.255.255 import-route direct undo synchronization peer 12.12.12.2 as-number 100 peer 13.13.13.3 as-number 100 #Return[R2-bgp]dis th#bgp 100 router-id 2.2.2.2 network 2.2.2.2 255.255.255.255 import-route direct undo synchronization peer 12.12.12.1 as-number 100 peer 24.24.24.4 as-number 100 peer 12.12.12.1 reflect-client#[R3-bgp]dis th#bgp 100 router-id 3.3.3.3 network 3.3.3.3 255.255.255.255 import-route direct undo synchronization peer 13.13.13.1 as-number 100 peer 35.35.35.5 as-number 100 peer 13.13.13.1 reflect-client#Return[R4-bgp]dis th#bgp 100 router-id 4.4.4.4 network 4.4.4.4 255.255.255.255 import-route direct undo synchronization peer 24.24.24.2 as-number 100 peer 45.45.45.5 as-number 100 peer 24.24.24.2 reflect-client#Return[R5-bgp]dis th#bgp 100 router-id 5.5.5.5 network 5.5.5.5 255.255.255.255 import-route direct undo synchronization peer 45.45.45.4 as-number 100 peer 35.35.35.3 as-number 100 #Return查看R1的bgp路由表*>i 5.5.5.5/32 35.35.35.5 0 100 0 i * i 45.45.45.5 0 100 0 i为什么优选35.35.35.5的路由呢？[R1-bgp]dis bgp routing-table 5.5.5.5 BGP local router ID : 1.1.1.1 Local AS number : 100 Paths: 2 available, 1 best BGP routing table entry information of 5.5.5.5/32: From : 13.13.13.3 (3.3.3.3) Relay Nexthop : 13.13.13.3 Original nexthop: 35.35.35.5 AS-path : (null) Origin : igp Attribute value : MED 0, localpref 100, pref-val 0, pre 255 State : valid, internal, best, Originator : 5.5.5.5 Cluster list : 3.3.3.3 Not advertised to any peers yet BGP routing table entry information of 5.5.5.5/32: From : 12.12.12.2 (2.2.2.2) Relay Nexthop : 12.12.12.2 Original nexthop: 45.45.45.5 AS-path : (null) Origin : igp Attribute value : MED 0, localpref 100, pref-val 0, pre 255 State : valid, internal, Originator : 5.5.5.5 Cluster list : 2.2.2.2, 4.4.4.4 Not advertised to any peers yet因为 来自R3的路由5.5.5.5的Cluster list值比较短！下面是优选ORIGINATOR_ID最小的路由去掉R4上的反射配置！查看R1的45.45.45.0bgp路由表*>i 45.45.45.0/24 24.24.24.4 0 100 0 ? * i 35.35.35.5 0 100 0 ?[R1-bgp]dis bgp routing-table 45.45.45.0 BGP local router ID : 1.1.1.1 Local AS number : 100 Paths: 2 available, 1 best BGP routing table entry information of 45.45.45.0/24: From : 12.12.12.2 (2.2.2.2) Relay Nexthop : 12.12.12.2 Original nexthop: 24.24.24.4 AS-path : (null) Origin : incomplete Attribute value : MED 0, localpref 100, pref-val 0, pre 255 State : valid, internal, best, Originator : 4.4.4.4 Cluster list : 2.2.2.2 Not advertised to any peers yet BGP routing table entry information of 45.45.45.0/24: From : 13.13.13.3 (3.3.3.3) Relay Nexthop : 13.13.13.3 Original nexthop: 35.35.35.5 AS-path : (null) Origin : incomplete Attribute value : MED 0, localpref 100, pref-val 0, pre 255 State : valid, internal, Originator : 5.5.5.5 Cluster list : 3.3.3.3 Not advertised to any peers yetORIGINATOR_ID这个值默认选router id本文出自 “cz涛声依旧” 博客，请务必保留此出处http://cztsyj.blog.51cto.com/1424318/555037
[R4]dis cu conf bgp#bgp 65002 confederation id 200 confederation peer-as 65003 network 4.4.4.4 255.255.255.255 undo synchronization peer 2.2.2.2 as-number 65002 peer 3.3.3.3 as-number 65003 peer 2.2.2.2 connect-interface LoopBack0 peer 3.3.3.3 connect-interface LoopBack0#Return查看r2r4的bgp路由表[R4]dis bgp routing-table Total Number of Routes: 5 BGP Local router ID is 4.4.4.4 Status codes: * - valid, > - best, d - damped, h - history, i - internal, s - suppressed, S - Stale Origin : i - IGP, e - EGP, ? - incomplete Network NextHop MED LocPrf PrefVal Path/Ogn *>i 1.1.1.1/32 3.3.3.3 0 100 0 (65003) 100i * i 2.2.2.2 0 100 0 100i i 2.2.2.2/32 2.2.2.2 0 100 0 i i 3.3.3.3/32 3.3.3.3 0 100 0 (65003)i *> 4.4.4.4/32 0.0.0.0 0 0 i[R2-bgp]dis bgp routing-table Total Number of Routes: 4 BGP Local router ID is 2.2.2.2 Status codes: * - valid, > - best, d - damped, h - history, i - internal, s - suppressed, S - Stale Origin : i - IGP, e - EGP, ? - incomplete Network NextHop MED LocPrf PrefVal Path/Ogn *> 1.1.1.1/32 12.12.12.1 0 0 100i * i 3.3.3.3 0 100 0 (65003) 100i *> 2.2.2.2/32 0.0.0.0 0 0 i i 4.4.4.4/32 4.4.4.4 0 100 0 i上述现象可知ebgp>联盟>ibgp优选CLUSTER_LIST长度最短的路由；优选ORIGINATOR_ID最小的路由；这两条原则我本想还用原来的拓扑来演示，可是遗憾没找到解决方法，重新画了一个，大家将就看
R2R3R4做反射基本配置：[R1-bgp]dis th#bgp 100 router-id 1.1.1.1 dampening network 1.1.1.1 255.255.255.255 import-route direct undo synchronization peer 12.12.12.2 as-number 100 peer 13.13.13.3 as-number 100 #Return[R2-bgp]dis th#bgp 100 router-id 2.2.2.2 network 2.2.2.2 255.255.255.255 import-route direct undo synchronization peer 12.12.12.1 as-number 100 peer 24.24.24.4 as-number 100 peer 12.12.12.1 reflect-client#[R3-bgp]dis th#bgp 100 router-id 3.3.3.3 network 3.3.3.3 255.255.255.255 import-route direct undo synchronization peer 13.13.13.1 as-number 100 peer 35.35.35.5 as-number 100 peer 13.13.13.1 reflect-client#Return[R4-bgp]dis th#bgp 100 router-id 4.4.4.4 network 4.4.4.4 255.255.255.255 import-route direct undo synchronization peer 24.24.24.2 as-number 100 peer 45.45.45.5 as-number 100 peer 24.24.24.2 reflect-client#Return[R5-bgp]dis th#bgp 100 router-id 5.5.5.5 network 5.5.5.5 255.255.255.255 import-route direct undo synchronization peer 45.45.45.4 as-number 100 peer 35.35.35.3 as-number 100 #Return查看R1的bgp路由表*>i 5.5.5.5/32 35.35.35.5 0 100 0 i * i 45.45.45.5 0 100 0 i为什么优选35.35.35.5的路由呢？[R1-bgp]dis bgp routing-table 5.5.5.5 BGP local router ID : 1.1.1.1 Local AS number : 100 Paths: 2 available, 1 best BGP routing table entry information of 5.5.5.5/32: From : 13.13.13.3 (3.3.3.3) Relay Nexthop : 13.13.13.3 Original nexthop: 35.35.35.5 AS-path : (null) Origin : igp Attribute value : MED 0, localpref 100, pref-val 0, pre 255 State : valid, internal, best, Originator : 5.5.5.5 Cluster list : 3.3.3.3 Not advertised to any peers yet BGP routing table entry information of 5.5.5.5/32: From : 12.12.12.2 (2.2.2.2) Relay Nexthop : 12.12.12.2 Original nexthop: 45.45.45.5 AS-path : (null) Origin : igp Attribute value : MED 0, localpref 100, pref-val 0, pre 255 State : valid, internal, Originator : 5.5.5.5 Cluster list : 2.2.2.2, 4.4.4.4 Not advertised to any peers yet因为 来自R3的路由5.5.5.5的Cluster list值比较短！下面是优选ORIGINATOR_ID最小的路由去掉R4上的反射配置！查看R1的45.45.45.0bgp路由表*>i 45.45.45.0/24 24.24.24.4 0 100 0 ? * i 35.35.35.5 0 100 0 ?[R1-bgp]dis bgp routing-table 45.45.45.0 BGP local router ID : 1.1.1.1 Local AS number : 100 Paths: 2 available, 1 best BGP routing table entry information of 45.45.45.0/24: From : 12.12.12.2 (2.2.2.2) Relay Nexthop : 12.12.12.2 Original nexthop: 24.24.24.4 AS-path : (null) Origin : incomplete Attribute value : MED 0, localpref 100, pref-val 0, pre 255 State : valid, internal, best, Originator : 4.4.4.4 Cluster list : 2.2.2.2 Not advertised to any peers yet BGP routing table entry information of 45.45.45.0/24: From : 13.13.13.3 (3.3.3.3) Relay Nexthop : 13.13.13.3 Original nexthop: 35.35.35.5 AS-path : (null) Origin : incomplete Attribute value : MED 0, localpref 100, pref-val 0, pre 255 State : valid, internal, Originator : 5.5.5.5 Cluster list : 3.3.3.3 Not advertised to any peers yetORIGINATOR_ID这个值默认选router id本文出自 “cz涛声依旧” 博客，请务必保留此出处http://cztsyj.blog.51cto.com/1424318/555037
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