Details

The route processor handles traffic destined to the switch-the key component used to build forwarding paths and is instrumental with all network management functions. Hence, any disruption or DoS attack to the route processor can result in mission critical network outages.

Solution

Step 1: Configure the ACL for any external interfaces as shown in the example below:

SW1(config)#ip access-list extended EXTERNAL_ACL
SW1(config-ext-nacl)#permit tcp host x.11.1.1 eq bgp host x.11.1.2
SW1(config-ext-nacl)#permit tcp host x.11.1.1 host x.11.1.2 eq bgp
SW1(config-ext-nacl)#permit icmp host x.11.1.1 host x.11.1.2 echo
SW1(config-ext-nacl)#permit icmp host x.11.1.1 host x.11.1.2 echo-reply
SW1(config-ext-nacl)#deny ip any host x.11.1.1 log-input
SW1(config-ext-nacl)#permit …
…
…
…
SW1(config-ext-nacl)#deny ip any any log-input

Step 2: Configure the ACL for any external interfaces as shown in the example below:

SW1(config)#ip access-list extended INTERNAL_ACL
SW1(config-ext-nacl)#permit ospf host 10.1.12.1 host 10.1.12.2
SW1(config-ext-nacl)#permit tcp 10.2.1.0 0.0.0.255 host 10.1.12.2 eq 22
SW1(config-ext-nacl)#permit tcp 10.2.1.0 0.0.0.255 host 10.1.12.2 eq tacacs
SW1(config-ext-nacl)#permit udp 10.2.1.0 0.0.0.255 host 10.1.12.2 eq snmp
SW1(config-ext-nacl)#permit udp 10.2.1.0 0.0.0.255 host 10.1.12.2 eq ntp
SW1(config-ext-nacl)#deny ip any host 10.1.12.2 log-input
SW1(config-ext-nacl)#permit …
…
…
…
SW1(config-ext-nacl)#permit ip any any log-input
SW1(config-ext-nacl)#exit

Note: Best practice is to configure the ACL statements relative to traffic destined to the switch first followed by ACL statements for transit traffic.

Step 3: Apply the ACLs to the appropriate interface as shown in the example below:

SW1(config)#int g0/2
SW1(config-if)#ip access-group EXTERNAL_ACL in
SW1(config)#int g0/3
SW1(config-if)#ip access-group INTERNAL_ACL in

Supportive Information

The following resource is also helpful.

• https://dl.dod.cyber.mil/wp-content/uploads/stigs/zip/U_Cisco_IOS_XE_Switch_Y21M04_STIG.zip

This security hardening control applies to the following category of controls within NIST 800-53: System and Communications Protection.This control applies to the following type of system Cisco.

References

• 800-53|SC-7a.
• CAT|I
• CCI|CCI-001097
• Rule-ID|SV-220996r622190_rule
• STIG-ID|CISC-RT-000130
• STIG-Legacy|SV-110813
• STIG-Legacy|V-101709
• Vuln-ID|V-220996

Source

• Tenable.com/audits