02 BGP地址聚合

实验目的

通过本实验可以掌握
（1）启动BGP 路由进程
（2）BGP 中通告网络
（3）EBGP 邻居配置
（4）BGP 地址聚合配置和调试
（5）地址聚合中参数“as-set”含义
（6）地址聚合中参数“summary-only”含义
（7）地址聚合中参数“suppress-map”含义

实验拓扑

实验步骤

本实验实现在路由器R2 上将路由器R1 和路由器R3 通告的环回接口的路由进行地址聚合，并通告给路由器R4。在路由器R1、R3、R4 配置静态路由实现网络互通。

1.配置IP地址

# '''R1'''
conf t
int l0
ip add 1.1.0.1 255.255.255.0
no sh
int l1
ip add 1.1.1.1 255.255.255.0
no sh
int f0/0
ip add 12.12.12.1 255.255.255.0
no sh
# '''R2'''
conf t
int f0/0
ip add 12.12.12.2 255.255.255.0
no sh
int f0/1
ip add 23.23.23.2 255.255.255.0
no sh
int f1/0
ip add 24.24.24.2 255.255.255.0
no sh
# '''R3'''
conf t
int l0
ip add 1.1.2.3 255.255.255.0
no sh
int l1
ip add 1.1.3.3 255.255.255.0
no sh
int f0/1
ip add 23.23.23.3 255.255.255.0
no sh
# '''R4'''
conf t
int l0
ip add 4.4.4.4 255.255.255.0
no sh
int f0/1
ip add 24.24.24.4 255.255.255.0
no sh

2.配置BGP

# '''R1'''
router bgp 100
no synchronization
no auto-summary
bgp router-id 1.1.1.1
neighbor 12.12.12.2 remote-as 200
network 1.1.0.0 mask 255.255.255.0
network 1.1.1.0 mask 255.255.255.0
exit
ip route 24.24.24.0 255.255.255.0 12.12.12.2
ip route 23.23.23.0 255.255.255.0 12.12.12.2
exit
# '''R2'''
# '''aggregate-address 1.1.0.0 255.255.252.0 配置地址聚合
router bgp 200
no synchronization
no auto-summary
bgp router-id 2.2.2.2
neighbor 12.12.12.1 remote-as 100
neighbor 23.23.23.3 remote-as 300
neighbor 24.24.24.4 remote-as 400
aggregate-address 1.1.0.0 255.255.252.0
# '''R3'''
router bgp 300
no synchronization
no auto-summary
bgp router-id 3.3.3.3
neighbor 23.23.23.2 remote-as 200
network 1.1.2.0 mask 255.255.255.0
network 1.1.3.0 mask 255.255.255.0
exit
ip route 12.12.12.0 255.255.255.0 23.23.23.2
ip route 24.24.24.0 255.255.255.0 23.23.23.2
# '''R4'''
router bgp 400
no synchronization
no auto-summary
bgp router-id 4.4.4.4
neighbor 24.24.24.2 remote-as 200
network 4.4.4.0 mask 255.255.255.0
exit
ip route 12.12.12.0 255.255.255.0 24.24.24.2
ip route 23.23.23.0 255.255.255.0 24.24.24.2
exit

实验调试

(1) 在路由器R1、R4上查看BGP表

R1#show ip bgp
BGP table version is 7, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incompleteNetwork          Next Hop            Metric LocPrf Weight Path
*> 1.1.0.0/24       0.0.0.0                  0         32768 i
*> 1.1.0.0/22       12.12.12.2               0             0 200 i
*> 1.1.1.0/24       0.0.0.0                  0         32768 i
*> 1.1.2.0/24       12.12.12.2                             0 200 300 i
*> 1.1.3.0/24       12.12.12.2                             0 200 300 i
*> 4.4.4.0/24       12.12.12.2                             0 200 400 i
R4#show ip bgp
BGP table version is 7, local router ID is 4.4.4.4
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incompleteNetwork          Next Hop            Metric LocPrf Weight Path
*> 1.1.0.0/24       24.24.24.2                             0 200 100 i
*> 1.1.0.0/22       24.24.24.2               0             0 200 i
*> 1.1.1.0/24       24.24.24.2                             0 200 100 i
*> 1.1.2.0/24       24.24.24.2                             0 200 300 i
*> 1.1.3.0/24       24.24.24.2                             0 200 300 i
*> 4.4.4.0/24       0.0.0.0                  0         32768 i
# 以上输出表明：
① 路由器R1、R4 收到“1.1.0.0/22”聚合路由，通过AS-PATH 属性可以看出，执行地址聚合的路由器R2 成为新路由的创造者，原来AS-PATH 属性丢失；
② 路由器R4 同时也收到4 条明细路由，在显示的AS-PATH 序列中，路由的始发AS 在列表的末端（右侧），每个收到该路由，并把它传递给其它AS 的BGP 对等体会把它自己的AS 追加在列表的开头（左侧）；
③ BGP 路由器下一跳为“0.0.0.0”，表示该BGP 路由起源本地，Weight 值为“32768”；
④ 因为所有BGP 路由条目的代码为“*>”，所以所有BGP 路由条目都为最优。

(2) as-set 参数

# “as-set”可以使BGP 聚合路由不丢失原来的AS-PATH 属性，从而避免路由环路，在路由器R2 配置as-set参数，然后再次查看R1、R4的BGP表
R2(config-router)#aggregate-address 1.1.0.0 255.255.252.0 as-set
R1#show ip bgp
BGP table version is 8, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incompleteNetwork          Next Hop            Metric LocPrf Weight Path
*> 1.1.0.0/24       0.0.0.0                  0         32768 i
*> 1.1.1.0/24       0.0.0.0                  0         32768 i
*> 1.1.2.0/24       12.12.12.2                             0 200 300 i
*> 1.1.3.0/24       12.12.12.2                             0 200 300 i
*> 4.4.4.0/24       12.12.12.2                             0 200 400 i
R4#show ip bgp
BGP table version is 8, local router ID is 4.4.4.4
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incompleteNetwork          Next Hop            Metric LocPrf Weight Path
*> 1.1.0.0/24       24.24.24.2                             0 200 100 i
*> 1.1.0.0/22       24.24.24.2               0             0 200 {100,300} i
*> 1.1.1.0/24       24.24.24.2                             0 200 100 i
*> 1.1.2.0/24       24.24.24.2                             0 200 300 i
*> 1.1.3.0/24       24.24.24.2                             0 200 300 i
*> 4.4.4.0/24       0.0.0.0                  0         32768 i
# 以上输出表明：
① 路由器R4 上收到的汇总路由“1.1.0.0/22”中，AS-PATH 包含了被聚合路由中所有的AS 号码的集合“{100,300}”；
② 聚合路由正是由于携带了所有的AS，所以在路由器R1 的BGP 表中没有出现，当然在路由器R3 的BGP 表中也不会出现。

# BGP 使用AS-PATH 属性作为路由更新的一部分来确保没有路由环路。因为在BGP 对等体之间传递的每条路由都携带它所经过的AS 号码序列表，如果该路由被通告给它始发的AS，该AS 路由器将在AS 序列表中看到自己的AS，它将不接受该路由。以下的输出充分的说明了这一点；
R2#show ip bgp neighbor 12.12.12.1 advertised-routes
BGP table version is 8, local router ID is 2.2.2.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incompleteNetwork          Next Hop            Metric LocPrf Weight Path
*> 1.1.0.0/24       12.12.12.1               0             0 100 i
*> 1.1.0.0/22       0.0.0.0                       100  32768 {100,300} i
*> 1.1.1.0/24       12.12.12.1               0             0 100 i
*> 1.1.2.0/24       23.23.23.3               0             0 300 i
*> 1.1.3.0/24       23.23.23.3               0             0 300 i
*> 4.4.4.0/24       24.24.24.4               0             0 400 iTotal number of prefixes 6
# 以上输出表明路由器R2 仍然向邻居12.12.12.1 发送聚合路由“1.1.0.0/22”。
R1#show ip bgp neighbors 12.12.12.2 received-routes
% Inbound soft reconfiguration not enabled on 12.12.12.2
R1#conf t
R1(config)#router bgp 100
R1(config-router)#neighbor 12.12.12.2 soft-reconfiguration inbound
R1(config-router)#exit
R1(config)#exit
R1#show ip bgp neighbor 12.12.12.2 received-routes
BGP table version is 8, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incompleteNetwork          Next Hop            Metric LocPrf Weight Path
*> 1.1.2.0/24       12.12.12.2                             0 200 300 i
*> 1.1.3.0/24       12.12.12.2                             0 200 300 i
*> 4.4.4.0/24       12.12.12.2                             0 200 400 iTotal number of prefixes 3
# 以上输出表明路由器R1 没有接收聚合路由“1.1.0.0/22”，因为它发现聚合路由条目中的AS-PATH 属性列表“{100,300}”中包含自己的AS 号码100，所以不接收。同理，路由器R3 也不会接收该聚合路由条目。
# 要执行“show ip bgp neighbors 12.12.12.2 received-routes”命令，必须完成下面这条命令：
R1(config-router)#neighbor 12.12.12.2 soft-reconfiguration inbound

(3) summary-only 参数

# 如果在路由器R4 上只想看到汇总路由，没有明细路由，“summary-only”参数可以实现，在路由器R2 上的配置如下；
R2(config-router)#aggregate-address 1.1.0.0 255.255.252.0 as-set summary-only
R2(config-router)#do show ip bgp
BGP table version is 18, local router ID is 2.2.2.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incompleteNetwork          Next Hop            Metric LocPrf Weight Path
s> 1.1.0.0/24       12.12.12.1               0             0 100 i
*> 1.1.0.0/22       0.0.0.0                       100  32768 {100,300} i
s> 1.1.1.0/24       12.12.12.1               0             0 100 i
s> 1.1.2.0/24       23.23.23.3               0             0 300 i
s> 1.1.3.0/24       23.23.23.3               0             0 300 i
*> 4.4.4.0/24       24.24.24.4               0             0 400 i
R4#show ip bgp
BGP table version is 18, local router ID is 4.4.4.4
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incompleteNetwork          Next Hop            Metric LocPrf Weight Path
*> 1.1.0.0/22       24.24.24.2               0             0 200 {100,300} i
*> 4.4.4.0/24       0.0.0.0                  0         32768 i
# 以上输出表明：
① 路由器R2 上所有被聚合的明细路由被标记为“s”，表示被抑制，不被发送；
② 路由器R4 只收到一跳聚合路由“1.1.0.0/22 ”。如果不加“as-set”参数，则路由器R1、R3 也会收到该聚合路由。

(4) suppress-map 参数

# 如果有特殊的需求，在聚合后只抑制部分明细路由条目，参数“suppress-map”可以完成。本实验要求路由器R2 地址聚合后，要求路由器R1 的两条明细路由被抑制，而路由器R3 的明细路由要求传递给路由器R4，路由器R2 配置步骤如下：
R2(config)#ip prefix-list 1 permit 1.1.0.0/24
R2(config)#ip prefix-list 1 permit 1.1.1.0/24
R2(config)#route-map sup permit 10
R2(config-route-map)#match ip address prefix-list 1
R2(config-route-map)#router bgp 200
R2(config-router)#$ddress 1.1.0.0 255.255.252.0 as-set suppress-map sup
R1#show ip bgp
BGP table version is 12, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incompleteNetwork          Next Hop            Metric LocPrf Weight Path
*> 1.1.0.0/24       0.0.0.0                  0         32768 i
*> 1.1.1.0/24       0.0.0.0                  0         32768 i
*> 1.1.2.0/24       12.12.12.2                             0 200 300 i
*> 1.1.3.0/24       12.12.12.2                             0 200 300 i
*> 4.4.4.0/24       12.12.12.2                             0 200 400 i
R2#show ip bgp
BGP table version is 24, local router ID is 2.2.2.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incompleteNetwork          Next Hop            Metric LocPrf Weight Path
s> 1.1.0.0/24       12.12.12.1               0             0 100 i
*> 1.1.0.0/22       0.0.0.0                       100  32768 {100,300} i
s> 1.1.1.0/24       12.12.12.1               0             0 100 i
*> 1.1.2.0/24       23.23.23.3               0             0 300 i
*> 1.1.3.0/24       23.23.23.3               0             0 300 i
*> 4.4.4.0/24       24.24.24.4               0             0 400 i
R3#show ip bgp
BGP table version is 14, 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, ? - incompleteNetwork          Next Hop            Metric LocPrf Weight Path
*> 1.1.2.0/24       0.0.0.0                  0         32768 i
*> 1.1.3.0/24       0.0.0.0                  0         32768 i
*> 4.4.4.0/24       23.23.23.2                             0 200 400 i
R4#show ip bgp
BGP table version is 20, local router ID is 4.4.4.4
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incompleteNetwork          Next Hop            Metric LocPrf Weight Path
*> 1.1.0.0/22       24.24.24.2               0             0 200 {100,300} i
*> 1.1.2.0/24       24.24.24.2                             0 200 300 i
*> 1.1.3.0/24       24.24.24.2                             0 200 300 i
*> 4.4.4.0/24       0.0.0.0                  0         32768 i
# 以上输出表明：
① 由于在路由器R2 上将路由器R1 的明细路由“1.1.0.0/24”和“1.1.1.0/24”抑制，所以路由器R3 和R4 不能收到；
② 由于在路由器R2 上没有将明细路由“1.1.2.0/24”和“1.1.3.0/24”抑制，又没有配置“summary-only”参数，所以四台路由器全部收到“1.1.2.0/24”和“1.1.3.0/24”的路由条目；
③ 由于配置了“as-set”参数，所以只有R4 收到汇总路由“1.1.0.0/22”。

实验总结

(1) aggregate-address

aggregate-address address mask [as-set] [as-confed-set] [summary-only] [suppress-map map-name] [advertise-map map-name] [attribute-map map-name]

no aggregate-address address mask [as-set] [as-confed-set] [summary-only] [suppress-map map-name] [advertise-map map-name] [attribute-map map-name]

Snytax	Description
address	Aggregate address.
mask	Aggregate mask.
as-set	(Optional) Generates autonomous system set path information.
as-confed-set	(Optional) Generates autonomous confederation set path information.
summary-only	(Optional) Filters all more-specific routes from updates.
suppress-map map-name	(Optional) Specifies the name of the route map used to select the routes to be suppressed.
advertise-map map-name	(Optional) Specifies the name of the route map used to select the routes to create AS_SET origin communities.
attribute-map map-name	(Optional) Specifies the name of the route map used to set the attribute of the aggregate route.

Command Default The atomic aggregate attribute is set automatically when an aggregate route is created with this command unless the as-set keyword is specified.

Command Modes Address family configuration (config-router-af)
Router configuration (config-router)

Conditional Aggregation Example
In the following example, a route map called MAP-ONE is created to match on an AS-path access list. The path advertised for this route will be an AS_SET consisting of elements contained in paths that are matched in the route map.

Router(config)# ip as-path access-list 1 deny ^1234_
Router(config)# ip as-path access-list 1 permit .*
Router(config)# !
Router(config)# route-map MAP-ONE
Router(config-route-map)# match ip as-path 1
Router(config-route-map)# exit
Router(config)# router bgp 50000
Router(config-router)# address-family ipv4
Router(config-router-af)# aggregate-address 10.0.0.0 255.0.0.0 as-set advertise-map
MAP-ONE
Router(config-router-af)# end

Related Commands

Command	Description
address-family ipv4 (BGP)	Places the router in address family configuration mode for configuring routing sessions such as BGP, RIP, or static routing sessions that use standard IPv4 address prefixes.
ip as-path access-list	Defines a BGP autonomous system path access list.
match ip address	Distributes any routes that have a destination network number address that is permitted by a standard or extended access list, and performs policy routing on packets.
neighbor distribute-list	Distributes BGP neighbor information in an access list.
route-map (IP)	Defines the conditions for redistributing routes from one routing protocol into another, or enables policy routing.

(2) ip prefix-list

To create a prefix list or to add a prefix-list entry, use the ip prefix-list command in global configuration mode. To delete a prefix-list entry, use the no form of this command.

ip prefix-list {list-name [seq number] {deny | permit} network/length [ge ge-length] [le le-length] | description description | sequence-number}
no ip prefix-list {list-name [seq number] [{deny | permit} network/length [ge ge-length] [le le-length]] | description description | sequence-number}

Snytax	Description
list-name	Configures a name to identify the prefix list. Do not use the word “detail” or “summary” as a list name because they are keywords in the show ip prefix-list command.
seq	(Optional) Applies a sequence number to a prefix-list entry.
number	(Optional) Integer from 1 to 4294967294. If a sequence number is not entered when configuring this command, default sequence numbering is applied to the prefix list. The number 5 is applied to the first prefix entry, and subsequent unnumbered entries are incremented by 5.
deny	Denies access for a matching condition.
permit	Permits access for a matching condition.
network/length	Configures the network address and the length of the network mask in bits. The network number can be any valid IP address or prefix. The bit mask can be a number from 1 to 32.
ge	(Optional) Specifies the lesser value of a range (the “from” portion of the range description) by applying the ge-length argument to the range specified. Note The ge keyword represents the greater than or equal to operator.
ge-length	(Optional) Represents the minimum prefix length to be matched.
le	(Optional) Specifies the greater value of a range (the “to” portion of the range description) by applying the le-length argument to the range specified. Note The le keyword represents the less than or equal to operator.
le-length	(Optional) Represents the maximum prefix length to be matched.
description	(Optional) Configures a descriptive name for the prefix list.
description	(Optional) Descriptive name of the prefix list, from 1 to 80 characters in length.
sequence-number	(Optional) Enables or disables the use of sequence numbers for prefix lists.

Command Default No prefix lists or prefix-list entries are created.

Command Modes Global configuration (config)