9,TCP SYN的防范。如:
A: 通过访问列表防范。
Router(Config)# no access-list 106
Router(Config)# access-list 106 permit tcp any 192.168.0.0 0.0.0.255 established
Router(Config)# access-list 106 deny ip any any log
Router(Config)# interface eth 0/2
Router(Config-if)# description "external Ethernet"
Router(Config-if)# ip address 192.168.1.254 255.255.255.0
Router(Config-if)# ip access-group 106 in
B:通过TCP截获防范。(这会给路由器产生一定负载)
Router(Config)# ip tcp intercept list 107
Router(Config)# access-list 107 permit tcp any 192.168.0.0 0.0.0.255
Router(Config)# access-list 107 deny ip any any log
Router(Config)# interface eth0
Router(Config)# ip access-group 107 in
10,LAND.C 进攻的防范。
Router(Config)# access-list 107 deny ip host 192.168.1.254 host 192.168.1.254 log
Router(Config)# access-list permit ip any any
Router(Config)# interface eth 0/2
Router(Config-if)# ip address 192.168.1.254 255.255.255.0
Router(Config-if)# ip access-group 107 in
11,Smurf进攻的防范。
Router(Config)# access-list 108 deny ip any host 192.168.1.255 log
Router(Config)# access-list 108 deny ip any host 192.168.1.0 log
12, ICMP协议的安全配置。对于进入ICMP流，我们要禁止ICMP协议的ECHO、Redirect、Mask request。也需要禁止TraceRoute命令的探测。对于流出的ICMP流，我们可以允许ECHO、Parameter Problem、Packet too big。还有TraceRoute命令的使用。
! outbound ICMP Control
Router(Config)# access-list 110 deny icmp any any echo log
Router(Config)# access-list 110 deny icmp any any redirect log
Router(Config)# access-list 110 deny icmp any any mask-request log
Router(Config)# access-list 110 permit icmp any any
! Inbound ICMP Control
Router(Config)# access-list 111 permit icmp any any echo
Router(Config)# access-list 111 permit icmp any any Parameter-problem
Router(Config)# access-list 111 permit icmp any any packet-too-big
Router(Config)# access-list 111 permit icmp any any source-quench
Router(Config)# access-list 111 deny icmp any any log
! Outbound TraceRoute Control
Router(Config)# access-list 112 deny udp any any range 33400 34400
! Inbound TraceRoute Control
Router(Config)# access-list 112 permit udp any any range 33400 34400
13,DDoS(Distributed Denial of Service)的防范。
! The TRINOO DDoS system
Router(Config)# access-list 113 deny tcp any any eq 27665 log
Router(Config)# access-list 113 deny udp any any eq 31335 log
Router(Config)# access-list 113 deny udp any any eq 27444 log
! The Stacheldtraht DDoS system
Router(Config)# access-list 113 deny tcp any any eq 16660 log
Router(Config)# access-list 113 deny tcp any any eq 65000 log
! The TrinityV3 System
Router(Config)# access-list 113 deny tcp any any eq 33270 log
Router(Config)# access-list 113 deny tcp any any eq 39168 log
! The SubSeven DDoS system and some Variants
Router(Config)# access-list 113 deny tcp any any range 6711 6712 log
Router(Config)# access-list 113 deny tcp any any eq 6776 log
Router(Config)# access-list 113 deny tcp any any eq 6669 log
Router(Config)# access-list 113 deny tcp any any eq 2222 log
Router(Config)# access-list 113 deny tcp any any eq 7000 log
13,建议启用SSH，废弃掉Telnet。但只有支持并带有IPSec特征集的IOS才支持SSH。并且IOS12.0-IOS12.2仅支持SSH-V1。如下配置SSH服务的例子:
Router(Config)# config t
Router(Config)# no access-list 22
Router(Config)# access-list 22 permit 192.168.0.22
Router(Config)# access-list deny any
Router(Config)# username BluShin privilege 10 G00dPa55w0rd
! 设置SSH的超时间隔和尝试登录次数
Router(Config)# ip ssh timeout 90
Router(Config)# ip ssh anthentication-retries 2
Router(Config)# line vty 0 4
Router(Config-line)# access-class 22 in
Router(Config-line)# transport input ssh
Router(Config-line)# login local
Router(Config-line)# exit
!启用SSH服务，生成RSA密钥对。
Router(Config)# crypto key generate rsa
The name for the keys will be: router.blushin.org
Choose the size of the key modulus in the range of 360 to 2048 for your General Purpose Keys .Choosing a key modulus greater than 512 may take a few minutes.
How many bits in the modulus[512]: 2048
Generating RSA Keys...
