BGP之過濾，彙聚

要求：

1.在R2上過濾22.2.2.0/24 23.3.16.0/20這兩個網段

2.比較route-map，distribute-list， ip prefix-list過濾的差別

interface Loopback0

ip address 1.1.1.1 255.255.255.0

interface Loopback1

ip address 21.0.0.1 255.255.255.0

interface Loopback2

ip address 22.2.2.1 255.255.255.0

interface Loopback3

ip address 23.3.0.1 255.255.240.0

interface Loopback4

ip address 23.3.16.1 255.255.240.0

interface Loopback5

ip address 23.3.32.1 255.255.224.0

interface Loopback6

ip address 23.3.64.1 255.255.192.0

interface Loopback7

ip address 23.3.128.1 255.255.128.0

interface Ethernet0/0

ip address 12.1.1.1 255.255.255.0

half-duplex

router bgp 123

no synchronization

bgp router-id 1.1.1.1

bgp log-neighbor-changes

network 21.0.0.0 mask 255.255.255.0

network 22.2.2.0 mask 255.255.255.0

network 23.3.0.0 mask 255.255.240.0

network 23.3.16.0 mask 255.255.240.0

network 23.3.32.0 mask 255.255.224.0

network 23.3.64.0 mask 255.255.192.0

network 23.3.128.0 mask 255.255.128.0

neighbor 12.1.1.2 remote-as 110

no auto-summary

ip address 2.2.2.2 255.255.255.255

ip address 12.1.1.2 255.255.255.0

interface Ethernet0/1

ip address 23.1.1.2 255.255.255.0

interface Ethernet0/2

ip address 24.1.1.2 255.255.255.0

interface Ethernet0/3

ip address 25.1.1.2 255.255.255.0

router ospf 10

router-id 2.2.2.2

log-adjacency-changes

network 2.2.2.2 0.0.0.0 area 0

network 12.1.1.0 0.0.0.255 area 0

network 23.1.1.0 0.0.0.255 area 0

network 24.1.1.0 0.0.0.255 area 0

network 25.1.1.0 0.0.0.255 area 0

router bgp 110

neighbor 3.3.3.3 remote-as 110

neighbor 3.3.3.3 update-source Loopback0

neighbor 3.3.3.3 distribute-list liang out

neighbor 4.4.4.4 remote-as 110

neighbor 4.4.4.4 update-source Loopback0

neighbor 4.4.4.4 route-map liang out

neighbor 5.5.5.5 remote-as 110

neighbor 5.5.5.5 update-source Loopback0

neighbor 5.5.5.5 prefix-list liang out

neighbor 12.1.1.1 remote-as 123

ip prefix-list liang seq 5 deny 22.2.2.0/24

ip prefix-list liang seq 10 deny 23.3.16.0/20

ip prefix-list liang seq 15 permit 0.0.0.0/0 le 32

ip access-list extended liang

deny ip host 22.2.2.0 host 255.255.255.0

deny ip host 23.3.16.0 host 255.255.240.0

permit ip any any

route-map liang permit 10

match ip address liang

control-plane

R3#show ip bgp

BGP table version is 24, local router ID is 3.3.3.3

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

*>i21.0.0.0/24 12.1.1.1 0 100 0 123 i

*>i23.3.0.0/20 12.1.1.1 0 100 0 123 i

*>i23.3.32.0/19 12.1.1.1 0 100 0 123 i

*>i23.3.64.0/18 12.1.1.1 0 100 0 123 i

*>i23.3.128.0/17 12.1.1.1 0 100 0 123 i

R4#show ip bgp

BGP table version is 24, local router ID is 4.4.4.4

R5#show ip bgp

BGP table version is 34, local router ID is 5.5.5.5

總結：

1.route-map對于多條過濾條目，并沒有任何優勢比起ip prefix-list，distribute，ACL

2.推薦選用prefix過濾路由條目，因為prefix可以比對mask長度

3.過于路徑的過濾可以選用filter-list 及其正規表達式

4.對于過濾路由條目，R2上不能配置peer-group

1. advertise-map Set condition to advertise attribute

as-set Generate AS set path information

attribute-map Set attributes of aggregate

nlri Nlri aggregate applies to

route-map Set parameters of aggregate

summary-only Filter more specific routes from updates

suppress-map Conditionally filter more specific routes from update 差別及其用途

2.AS2有個10.1.3.0/24 AS3有個10.1.1.0/24，AS4有個10.1.2.0/24

步驟：

在R2上做彙聚

不做彙聚情況

R1#show ip bgp

BGP table version is 1, local router ID is 1.1.1.1

* i10.1.1.0/24 24.1.1.4 0 100 0 3 i

* i10.1.2.0/24 26.1.1.6 0 100 0 4 i

* i10.1.3.0/24 23.1.1.3 0 100 0 2 i

BGP table version is 4, local router ID is 1.1.1.1

*>i10.1.1.0/24 2.2.2.2 0 100 0 3 i

*>i10.1.2.0/24 2.2.2.2 0 100 0 4 i

*>i10.1.3.0/24 2.2.2.2 0 100 0 2 i

R2(config-router)#aggregate-address 10.1.1.0 255.255.252.0

BGP table version is 5, local router ID is 1.1.1.1

*>i10.1.0.0/22 2.2.2.2 0 100 0 i

R2#show ip bgp

BGP table version is 5, local router ID is 2.2.2.2

*> 10.1.0.0/22 0.0.0.0 32768 i

*> 10.1.1.0/24 24.1.1.4 0 3 i

*> 10.1.2.0/24 26.1.1.6 0 0 4 i

*> 10.1.3.0/24 23.1.1.3 0 0 2 i

預設的情況下明細聚合路由都傳遞，而聚合路由是0.0.0.0本地起源的。

預設的是原子聚合所謂的原子聚合就是說明路由已經被彙聚，預設的明細路由的屬性消失

R2(config-router)#aggregate-address 10.1.1.0 255.255.252.0 summary-only

BGP table version is 8, local router ID is 1.1.1.1

BGP table version is 8, local router ID is 2.2.2.2

s> 10.1.1.0/24 24.1.1.4 0 3 i

s> 10.1.2.0/24 26.1.1.6 0 0 4 i

s> 10.1.3.0/24 23.1.1.3 0 0 2 i

打上summary-only隻傳遞聚合路由，在聚合者路由上明細路由被抑制

這時我們說下suppress-map，我們想讓10.1.1.0/24路由不被抑制R2配置如下

access-list 100 permit ip host 10.1.1.0 host 255.255.255.0

route-map liang deny 10

match ip address 100

route-map liang permit 20

R2(config-router)#$1.1.0 255.255.252.0 summary-only suppress-map liang

BGP table version is 15, local router ID is 2.2.2.2

BGP table version is 15, local router ID is 1.1.1.1

假如我們把10.1.1.0/24抑制掉

Access-list 101 permit ip host 10.1.1.0 mask 255.255.255.0

route-map liang premit 10

Match ip add 101

記着在這不能再打 route-map liang permit 20如果這樣就是允許了就不能把這個條目抑制掉了

as-set

R2(config-router)#$ddress 10.1.1.0 255.255.252.0 summary-only as-set

BGP table version is 22, local router ID is 1.1.1.1

*>i10.1.0.0/22 2.2.2.2 0 100 0 {3,4,2} i

還原原來的明細路由屬性

attribute-map/route-map 定義控制聚合的屬性隻對聚合後的路由起作用

Extended IP access list 100

10 permit ip host 10.1.1.0 host 255.255.255.0 (1 match)

R2(config)#route-map test permit 10

R2(config-route-map)#ma

R2(config-route-map)#match ip add 101

R2(config-route-map)#set ?

as-path Prepend string for a BGP AS-path attribute

automatic-tag Automatically compute TAG value

comm-list set BGP community list (for deletion)

community BGP community attribute

dampening Set BGP route flap dampening parameters

default Set default information

extcommunity BGP extended community attribute

interface Output interface

ip IP specific information

ipv6 IPv6 specific information

level Where to import route

local-preference BGP local preference path attribute

metric Metric value for destination routing protocol

metric-type Type of metric for destination routing protocol

mpls-label Set MPLS label for prefix

nlri BGP NLRI type

origin BGP origin code

tag Tag value for destination routing protocol

traffic-index BGP traffic classification number for accounting

vrf Define VRF name

weight BGP weight for routing table

設定聚合後的屬性值

Advertise-map----隻對advertise-map裡面比對的路由進行聚合。當advertise-map裡面比對的明細路由全部消失後，即使聚合路由範圍内還有其他明細路由，聚合路由也将消失。當與as－set合用時，隻繼承advertise-map裡面比對的明細路由的屬性。

定義宣告沒有進來之前那些明細路由應該被聚合

As-set----讓聚合路由繼承明細路由的屬性，包括：as-path，local_preference，community，origin－code。與advertise-map合用，隻繼承advertise-map裡面比對的明細路由的屬性。

預設是産生的彙聚路由是本地始發的也就是下一跳0.0.0.0的路由，他會抑制掉彙聚之前AS路徑的資訊

打上AS-SET 會繼承明細路由的屬性

Attribute－map和route－map----這兩個參數一樣，可以将聚合路由的屬性清除掉（除了as-path屬性），添加自己需要添加的屬性。

隻影響聚合後的路由的屬性也就是給聚合路由加屬性不加as-set 預設是原子聚合

Summary-only----将聚合路由所包括的所有明細路由都抑制掉，被抑制的路由在bgp的轉發表裡，顯示為s，代表suppress的意思。發送更新時，隻發送聚合路由。可以與neighbor 1.1.1.1 unsuppress-map XX合用，對特定鄰居漏過特定的明細路由。

Suppress－map----将suppress－map裡面比對的路由抑制掉，被抑制的路由在bgp的轉發表裡，顯示為s，代表suppress的意思。發送更新時，隻發送聚合路由和沒有被抑制的明細路由。可以neighbor 1.1.1.1 unsuppress-map XX合用，對特定鄰居漏過特定的明細路由。

permit為抑制不轉發 deny為不抑制也就是轉發

本文轉自q狼的誘惑 51CTO部落格，原文連結：http://blog.51cto.com/liangrui/572745，如需轉載請自行聯系原作者

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