一、）配置示例：
拓扑:
R2-(S2/0)-----------------(S2/0)-R1(S2/1)---------------(S2/1)-R3
带有Established的扩展访问列表答应内部用户访问外部网络,而拒绝外部网络访问内部网络,而没带Established的标准访问列表和扩展访问列表没有这个特性.
这个示例首先用OSPF来使全网互联.
R1:
r1#sh run
*Mar 1 00:25:17.275: %SYS-5-CONFIG_I: Configured from console by console
Building configuration...
Current configuration : 1410 bytes
!
version 12.2
service timestamps debug datetime msec
service timestamps log datetime msec
no service passWord-encryption
!
hostname r1
!
logging queue-limit 100
!
ip subnet-zero
!
!
!
ip audit notify log
ip audit po max-events 100
mpls ldp logging neighbor-changes
!
!
!
!
!
!
!
!
!
!
!
!
no voice hpi capture buffer
no voice hpi capture destination
!
!
mta receive maximum-recipients 0
!
!
!
!
interface Loopback0
ip address 1.1.1.1 255.255.255.0
!
interface FastEthernet0/0
no ip address
shutdown
duplex auto
speed auto
!
interface FastEthernet1/0
no ip address
shutdown
duplex auto
speed auto
!
interface Serial2/0
ip address 12.1.1.1 255.255.255.0
encapsulation frame-relay
ip ospf network point-to-point
serial restart_delay 0
frame-relay map ip 12.1.1.2 102 broadcast
no frame-relay inverse-arp
!
interface Serial2/1
ip address 13.1.1.1 255.255.255.0
encapsulation frame-relay
ip ospf network point-to-point
serial restart_delay 0
frame-relay map ip 13.1.1.3 113 broadcast
!
interface Serial2/2
no ip address
shutdown
serial restart_delay 0
!
interface Serial2/3
no ip address
shutdown
serial restart_delay 0
!
router ospf 10
log-adjacency-changes
network 0.0.0.0 255.255.255.255 area 0
!
ip http server
no ip http secure-server
ip classless
!
!
!
!
!
call rsvp-sync
!
!
mgcp profile default
!
!
!
dial-peer cor custom
!
!
!
!
!
line con 0
line aux 0
line vty 0 4
no login
!
!
end
R2:
r2#sh run
Building configuration...
*Mar 1 00:27:29.871: %SYS-5-CONFIG_I: Configured from console by console
Current configuration : 1298 bytes
!
version 12.2
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname r2
!
logging queue-limit 100
!
ip subnet-zero
!
!
!
ip audit notify log
ip audit po max-events 100
mpls ldp logging neighbor-changes
!
!
no voice hpi capture buffer
no voice hpi capture destination
!
!
mta receive maximum-recipients 0
!
!
interface Loopback0
ip address 2.2.2.2 255.255.255.0
!
interface FastEthernet0/0
no ip address
shutdown
duplex auto
speed auto
!
interface FastEthernet1/0
no ip address
shutdown
duplex auto
speed auto
!
interface Serial2/0
ip address 12.1.1.2 255.255.255.0
encapsulation frame-relay
ip ospf network point-to-point
serial restart_delay 0
frame-relay map ip 12.1.1.1 201 broadcast
no frame-relay inverse-arp
!
interface Serial2/1
no ip address
shutdown
serial restart_delay 0
!
interface Serial2/2
no ip address
shutdown
serial restart_delay 0
!
interface Serial2/3
no ip address
shutdown
serial restart_delay 0
!
router ospf 10
log-adjacency-changes
network 0.0.0.0 255.255.255.255 area 0
!
ip http server
no ip http secure-server
ip classless
!
!
!
!
!
call rsvp-sync
!
!
mgcp profile default
!
!
!
dial-peer cor custom
!
line con 0
line aux 0
line vty 0 4
no login
!
!
end
r3
r3#sh run
Building configuration...
Current configuration : 1298 bytes
!
version 12.2
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname r3
!
logging queue-limit 100
!
ip subnet-zero
!
!
!
ip audit notify log
ip audit po max-events 100
mpls ldp logging neighbor-changes
!
!
!
!
!
!
!
!
!
!
!
!
no voice hpi capture buffer
no voice hpi capture destination
!
!
mta receive maximum-recipients 0
!
!
!
!
interface Loopback0
ip address 3.3.3.3 255.255.255.0
!
interface FastEthernet0/0
no ip address
shutdown
duplex auto
speed auto
!
interface FastEthernet1/0
no ip address
shutdown
duplex auto
speed auto
!
interface Serial2/0
no ip address
shutdown
serial restart_delay 0
!
interface Serial2/1
ip address 13.1.1.3 255.255.255.0
encapsulation frame-relay
ip ospf network point-to-point
serial restart_delay 0
frame-relay map ip 13.1.1.1 311 broadcast
no frame-relay inverse-arp
!
interface Serial2/2
no ip address
shutdown
serial restart_delay 0
!
interface Serial2/3
no ip address
shutdown
serial restart_delay 0
!
router ospf 10
log-adjacency-changes
network 0.0.0.0 255.255.255.255 area 0
!
ip http server
no ip http secure-server
ip classless
!
!
!
!
!
call rsvp-sync
!
!
mgcp profile default
!
!
!
dial-peer cor custom
!
!
!
!
!
line con 0
line aux 0
line vty 0 4
no login
!
!
end
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二、）监视和测试配置:
我们让R2作为内部网络,R3作为内部网络,以下配置使R2发起访问R3没问题,从R3访问R2则被拒绝.注重这个配置方案是针对基于TCP的应用,任何TCP通讯都是双向的,从R2发起的访问外部网络之后,外部网络的流量得以通过,这个时候TCP报文,ACK或RST位被设置为1
R1(configure)Access-list 101 permit tcp any any established log-input
R1(configure)access-list 101 permit ospf any any
R1(configure)access-list 101 deny ip any any log-input
R1(configure)int s2/1
R1(configure-if)ip access-group 101 in
以上log-input是为了显示监视数据报文被过滤的情况,接下来用debug ip packet detailed来监视报文经过R1的情况,应该路由器还有OSPF报文产生,因此我们对DEBUG信息做了限制.
r1(config)#access-list 102 permit tcp any any
我们这样做 让R2发起telnet访问R3
r1#telnet 3.3.3.3
Trying 3.3.3.3 ... Open
r3>
*Mar 1 00:55:53.003: IP: tableid=0, s=13.1.1.1 (local), d=3.3.3.3 (Serial2/1), routed via RIB
*Mar 1 00:55:53.003: IP: s=13.1.1.1 (local), d=3.3.3.3 (Serial2/1), len 44, sending
*Mar 1 00:55:53.007: TCP src=11001, dst=23, seq=2398697781, ack=0, win=4128 SYN
*Mar 1 00:55:53.179: %SEC-6-IPACCESSLOGP: list 101 permitted tcp 3.3.3.3(23) (Serial2/1 ) -> 13.1.1.1(11001), 1 packet
*Mar 1 00:55:53.183: IP: tableid=0, s=3.3.3.3 (Serial2/1), d=13.1.1.1 (Serial2/1), routed via RIB
*Mar 1 00:55:53.183: IP: s=3.3.3.3 (Serial2/1), d=13.1.1.1 (Serial2/1), len 44, rcvd 3
*Mar 1 00:55:53.187: TCP src=23, dst=11001, seq=949632690, ack=2398697782, win=4128 ACK SYN
*Mar 1 00:55:53.187: IP: tableid=0, s=13.1.1.1 (local), d=3.3.3.3 (Serial2/1), routed via RIB
*Mar 1 00:55:53.191: IP: s=13.1.1.1 (local), d=3.3.3.3 (Serial2/1), len 40, sending
*Mar 1 00:55:53.191: TCP src=11001, dst=23, seq=2398697782, ack=949632691, win=4128 ACK
*Mar 1 00:55:53.199: IP: tableid=0, s=13.1.1.1 (local), d=3.3.3.3 (Serial2/1), routed via RIB
*Mar 1 00:55:53.203: IP: s=13.1.1.1 (local), d=3.3.3.3 (Serial2/1), len 49, sending
*Mar 1 00:55:53.203: TCP src=11001, dst=23, seq=2398697782, ack=949632691, win=4128 ACK PSH
*Mar 1 00:55:53.207: IP: tableid=0, s=13.1.1.1 (local), d=3.3.3.3 (Serial2/1), routed via RIB
*Mar 1 00:55:53.211: IP: s=13.1.1.1 (local), d=3.3.3.3 (Serial2/1), len 40, sending
*Mar 1 00:55:53.215: TCP src=11001, dst=23, seq=2398697791, ack=949632691, win=4128 ACK
*Mar 1 00:55:53.455: IP: tableid=0, s=3.3.3.3 (Serial2/1), d=13.1.1.1 (Serial2/1), routed via RIB
*Mar 1 00:55:53.455: IP: s=3.3.3.3 (Serial2/1), d=13.1.1.1 (Serial2/1), len 52, rcvd 3
*Mar 1 00:55:53.459: TCP src=23, dst=11001, seq=949632691, ack=2398697791, win=4119 ACK PSH
*Mar 1 00:55:53.459: IP: tableid=0, s=3.3.3.3 (Serial2/1), d=13.1.1.1 (Serial2/1), routed via RIB
*Mar 1 00:55:53.463: IP: s=3.3.3.3 (Serial2/1), d=13.1.1.1 (Serial2/1), len 45, rcvd 3
*Mar 1 00:55:53.467: TCP src=23, dst=11001, seq=949632703, ack=2398697791, win=4119 ACK PSH
*Mar 1 00:55:53.467: IP: tableid=0, s=3.3.3.3 (Serial2/1), d=13.1.1.1 (Serial2/1), routed via RIB
*Mar 1 00:55:53.471: IP: s=3.3.3.3 (Serial2/1), d=13.1.1.1 (Serial2/1), len 43, rcvd 3
*Mar 1 00:55:53.471: TCP src=23, dst=11001, seq=949632708, ack=2398697791, win=4119 ACK PSH
*Mar 1 00:55:53.475: IP: tableid=0, s=3.3.3.3 (Serial2/1), d=13.1.1.1 (Serial2/1), routed via RIB
*Mar 1 00:55:53.479: IP: s=3.3.3.3 (Serial2/1), d=13.1.1.1 (Serial2/1), len 46, rcvd 3
*Mar 1 00:55:53.479: TCP src=23, dst=11001, seq=949632711, ack=2398697791, win=4119 ACK PSH
*Mar 1 00:55:53.483: IP: tableid=0, s=13.1.1.1 (local), d=3.3.3.3 (Serial2/1), routed via RIB
*Mar 1 00:55:53.487: IP: s=13.1.1.1 (local), d=3.3.3.3 (Serial2/1), len 43, sending
*Mar 1 00:55:53.487: TCP src=11001, dst=23, seq=2398697791, ack=949632717, win=4102 ACK PSH
*Mar 1 00:55:53.491: IP: tableid=0, s=13.1.1.1 (local), d=3.3.3.3 (Serial2/1), routed via RIB
*Mar 1 00:55:53.495: IP: s=13.1.1.1 (local), d=3.3.3.3 (Serial2/1), len 43, sending
*Mar 1 00:55:53.495: TCP src=11001, dst=23, seq=2398697794, ack=949632717, win=4102 ACK PSH
*Mar 1 00:55:53.499: IP: tableid=0, s=13.1.1.1 (local), d=3.3.3.3 (Serial2/1), routed via RIB
*Mar 1 00:55:53.503: IP: s=13.1.1.1 (local), d=3.3.3.3 (Serial2/1), len 49, sending
*Mar 1 00:55:53.503: TCP src=11001, dst=23, seq=2398697797, ack=949632717, win=4102 ACK PSH
*Mar 1 00:55:53.659: IP: tableid=0, s=3.3.3.3 (Serial2/1), d=13.1.1.1 (Serial2/1), routed via RIB
*Mar 1 00:55:53.663: IP: s=3.3.3.3 (Serial2/1), d=13.1.1.1 (Serial2/1), len 43, rcvd 3
*Mar 1 00:55:53.663: TCP src=23, dst=11001, seq=949632717, ack=2398697797, win=4113 ACK PSH
*Mar 1 00:55:53.867: IP: tableid=0, s=13.1.1.1 (local), d=3.3.3.3 (Serial2/1), routed via RIB
*Mar 1 00:55:53.867: IP: s=13.1.1.1 (local), d=3.3.3.3 (Serial2/1), len 40, sending
*Mar 1 00:55:53.871: TCP src=11001, dst=23, seq=2398697806, ack=949632720, win=4099 ACK
*Mar 1 00:55:53.963: IP: tableid=0, s=3.3.3.3 (Serial2/1), d=13.1.1.1 (Serial2/1), routed via RIB
*Mar 1 00:55:53.967: IP: s=3.3.3.3 (Serial2/1), d=13.1.1.1 (Serial2/1), len 40, rcvd 3
*Mar 1 00:55:53.967: TCP src=23, dst=11001, seq=949632720, ack=2398697806, win=4104 ACK
注重R3返回R2的数据报文得以通过,接下来我们测试从R3发起访问R2的情况
r3#telnet 2.2.2.2
Trying 2.2.2.2 ...
% Destination unreachable; gateway or host down
r1#
*Mar 1 01:02:22.779: %SEC-6-IPACCESSLOGP: list 101 denied tcp 13.1.1.3(11002) (Serial2/1 ) -> 2.2.2.2(23), 1 packet
*Mar 1 01:02:22.783: IP: s=13.1.1.3 (Serial2/1), d=2.2.2.2, len 44, access denied
*Mar 1 01:02:22.783: IP: tableid=0, s=13.1.1.1 (local), d=13.1.1.3 (Serial2/1), routed via RIB
*Mar 1 01:02:22.787: IP: s=13.1.1.1 (local), d=13.1.1.3 (Serial2/1), len 56, sending
*Mar 1 01:02:24.139: IP: s=12.1.1.2 (Serial2/0), d=224.0.0.5, len 80, rcvd 0
*Mar 1 01:02:24.315: IP: s=13.1.1.1 (local), d=224.0.0.5 (Serial2/1), len 80, sending broad/multicast
*Mar 1 01:02:25.139: IP: s=12.1.1.1 (local), d=224.0.0.5 (Serial2/0), len 80, sending broad/multicast
注重,TCP协议的第一次发送是SYN字段,这是用来同步预备建立一个新连接的两端主机,而ACK位由接收者置位从而向发送者表明数据已经成功接收.RST(reset)位说明什么时候重新启动连接.带Eetablished的扩展访问列表只答应ACK或RST位置1的TCP报文通过.
