路由器安全配置速查表（二）

文章作者 100test 发表时间 2007:03:14 13:15:14
来源 100Test.Com百考试题网

Specific Recommendations: Access Lists

1. Always start an access-list definition with the privileged command no

access-list nnn to clear out any previous versions of access list number

nnn.

fumtek(config)# no access-list 51

fumtek(config)# access-list 51 permit host 14.2.9.6

fumtek(config)# access-list 51 deny any log

2. Log access list port messages properly. To ensure that logs contain

correct port number information, use the port range arguments shown below

at the end of an access list.

access-list 106 deny udp any range 1 65535 any range 1 65535 log

access-list 106 deny tcp any range 1 65535 any range 1 65535 log

access-list 106 deny ip any any log

The last line is necessary to ensure that rejected packets of protocols

other than TCP and UDP are properly logged.

3. Enforce traffic address restrictions using access lists. On a border

router, allow only internal addresses to enter the router from the

internal interfaces, and allow only traffic destined for internal

addresses to enter the router from the outside (external interfaces).

Block illegal addresses at the outgoing interfaces. Besides preventing an

attacker from using the router to attack other sites, it helps identify

poorly configured internal hosts or networks. This approach may not be

feasible for complicated networks. [RFC 2827]

fumtek(config)# no access-list 101

fumtek(config)# access-list 101 permit ip 14.2.6.0 0.0.0.255 any

fumtek(config)# access-list 101 deny ip any any log

fumtek(config)# no access-list 102

fumtek(config)# access-list 102 permit ip any 14.2.6.0 0.0.0.255

fumtek(config)# access-list 102 deny ip any any log

fumtek(config)# interface eth 1

fumtek(config-if)# ip access-group 101 in

fumtek(config-if)# exit

fumtek(config)# interface eth 0

fumtek(config-if)# ip access-group 101 out

fumtek(config-if)# ip access-group 102 in

4. Block packets coming from the outside (untrusted network) that are

obviously fake or have source or destination addresses that are reserved,

for example networks 0.0.0.0/8, 10.0.0.0/8, 169.254.0.0/16, 172.16.0.0/20,

192.168.0.0/16. This protection should be part of the overall traffic

filtering at the interface attached to the external,

untrusted network. [RFC 1918]

5. Block incoming packets that claim to have a source address of any

internal (trusted) networks. This impedes TCP sequence number guessing and

other attacks. Incorporate this protection into the access lists applied

to interfaces facing any untrusted networks.

6. Drop incoming packets with loopback addresses, network 127.0.0.0/8.

These packets cannot be real.

7. If the network doesn’t need IP multicast, then block multicast packets.

8. Block broadcast packets. (Note that this may block DHCP and BOOTP

services, but these services should not be used on external interfaces and

certainly shouldn’t cross border routers.)

9. A number of remote probes and attacks use ICMP echo, redirect, and mask

request messages, block them. (A superior but more difficult approach is

to permit only necessary ICMP packet types.)

The example below shows one way to implement these recommendations.

North(config)# no access-list 107

North(config)# ! block our internal addresses

North(config)# access-list 107 deny ip 14.2.0.0 0.0.255.255 any log

North(config)# access-list 107 deny ip 14.1.0.0 0.0.255.255 any log

North(config)# ! block special/reserved addresses

North(config)# access-list 107 deny ip 127.0.0.0 0.255.255.255 any log

North(config)# access-list 107 deny ip 0.0.0.0 0.255.255.255 any log

North(config)# access-list 107 deny ip 10.0.0.0 0.255.255.255 any log

North(config)# access-list 107 deny ip 169.254.0.0 0.0.255.255 any log

North(config)# access-list 107 deny ip 172.16.0.0 0.15.255.255 any log

North(config)# access-list 107 deny ip 192.168.0.0 0.0.255.255 any log

North(config)# ! block multicast (if not used)

North(config)# access-list 107 deny ip 224.0.0.0 15.255.255.255 any

North(config)# ! block some ICMP message types

North(config)# access-list 107 deny icmp any any redirect log

North(config)# access-list 107 deny icmp any any echo log

North(config)# access-list 107 deny icmp any any mask-request log

North(config)# access-list 107 permit ip any 14.2.0.0 0.0.255.255

North(config)# access-list 107 permit ip any 14.1.0.0 0.0.255.255

North(config)# interface Eth 0/0

North(config-if)# description External interface

North(config-if)# ip access-group 107 in

10. Block incoming packets that claim to have the same destination and

source address (i.e. a ‘Land’ attack on the router itself). Incorporate

this protection into the access list used to restrict incoming traffic

into each interface, using a rule like the one shown below.

access-list 102 deny ip host 14.1.1.250

host 14.1.1.250 log

interface Eth 0/1

ip address 14.1.1.250 255.255.0.0

ip access-group 102 in

11. Configure an access list for the virtual terminal lines to control

Telnet access. See example commands below.

South(config)# no access-list 92

South(config)# access-list 92 permit 14.2.10.1

South(config)# access-list 92 permit 14.2.9.1

South(config)# line vty 0 4

South(config-line)# access-class 92 in

路由器安全配置速查表（三）

Specific Recommendations: Logging &. Debugging

1. Turn on the router’s logging capability, and use it to log errors and

blocked packets to an internal (trusted) syslog host. Make sure that the

router blocks syslog traffic from untrusted networks. See example commands

below.

Central(config)# logging on

Central(config)# logging 14.2.9.1

Central(config)# logging buffered

Central(config)# logging console critical

Central(config)# logging trap informational

Central(config)# logging facility local1

2. Configure the router to include time information in the logging.

Configure at least two different NTP servers to ensure availability of

good time information. This will allow an administrator to trace network

attacks more accurately. See example commands below.

East(config)# service timestamps log datetime localtime show-timezone msec

East(config)# clock timezone GMT 0

East(config)# ntp server 14.1.1.250

East(config)# ntp server 14.2.9.1

3. If your network requires SNMP, then configure an SNMP ACL and

hard-to-guess SNMP community strings. The example commands below show how

to remove the default community strings and set a better read-only

community string, with an ACL.

East(config)# no snmp community public ro

East(config)# no snmp community private rw

East(config)# no access-list 51

East(config)# access-list 51 permit 14.2.9.1

East(config)# snmp community BTRl8 never ro 51

Router Security Checklist

This security checklist is designed to help you review your router

security configuration, and remind you of any security area you might have missed.

Router security policy written, approved, distributed.

Router IOS version checked and up to date.

Router configuration kept off-line, backed up, access to it limited.

Router configuration is well-documented, commented.

Router users and passwords configured and maintained.

Password encryption in use, enable secret in use.

Enable secret difficult to guess, knowledge of it strictly limited. (if

not, change the enable secret immediately).

Access restrictions imposed on Console, Aux, VTYs.

Unneeded network servers and facilities disabled.

Necessary network services configured correctly (e.g. DNS)

Unused interfaces and VTYs shut down or disabled.

Risky interface services disabled.

Port and protocol needs of the network identified and checked.

Access lists limit traffic to identified ports and protocols.

Access lists block reserved and inappropriate addresses.

Static routes configured where necessary.

Routing protocols configured to use integrity mechanisms.

Logging enabled and log recipient hosts identified and configured.

Router’s time of day set accurately, maintained with NTP.

Logging set to include consistent time information.

Logs checked, reviewed, archived in accordance with local policy.

SNMP disabled or enabled with good community strings and ACLs.