Chapter 1 Cisco SDM Express
Supplementary Help
The configuration that will be delivered to the router to disable PAD is as follows:
no service pad
You can undo this fix using the Cisco SDM Security Audit feature. To learn how, see the Security Audit online help in Cisco SDM. For more information, click Cisco Router and Security Device Manager.
Disable TCP Small Servers Service
Cisco SDM Express disables small services whenever possible. By default, Cisco devices running Cisco IOS release 11.3 or earlier offer the “small services”: echo, chargen, and discard. (Small services are disabled by default in Cisco IOS software release 12.0 and later.) These services, especially their User Datagram Protocol (UDP) versions, are infrequently used for legitimate purposes, but they can be used to launch Denial of Service (DoS) and other attacks that would otherwise be prevented by packet filtering.
For example, an attacker might send a Domain Name System (DNS) packet, falsifying the source address to be a DNS server that would otherwise be unreachable, and falsifying the source port to be the DNS service port (port 53). If such a packet were sent to the router UDP echo port, the result would be the router sending a DNS packet to the server in question. No outgoing access list checks would be applied to this packet because it would be considered to be locally generated by the router itself.
Although most abuses of the small services can be avoided or made less dangerous by antispoofing access lists, the services should almost always be disabled in any router which is part of a firewall or lies in a
The configuration that will be delivered to the router to disable TCP small servers is as follows:
no service
You can undo this fix using the Cisco SDM Security Audit feature. To learn how, see the Security Audit online help in Cisco SDM. For more information, click Cisco Router and Security Device Manager.
| Cisco SDM Express |
