Blocking Non-Edge Protocols at the Edge Network Layer

Edge clients should be prevented from acting as servers for a number of IP services. If non-edge IP services accidently or maliciously attach to the edge of the network, they are capable of disrupting network operation. IP services should only be allowed where and when your network design requires. This section identifies ten IP Services you should consider blocking at the edge unless allowing them is part of your network architecture.

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Non-Edge Protocols

Protocol Policy Effect
DHCP Server Protocol Every network needs DHCP. Automatically mitigate the accidental or malicious connection of a DHCP server to the edge of your network to prevent DoS or data integrity issues, by blocking DHCP on the source port for this device.
DNS Server Protocol DNS is critical to network operations. Automatically protect your name servers from malicious attack or unauthorized spoofing and redirection, by blocking DNS on the source port for this device.
Routing Topology Protocols RIP, OSPF, and BGP topology protocols should only originate from authorized router connection points to ensure reliable network operations.
Router Source MAC and Router Source IP Address Routers and default gateways should not be moving around your network without approved change processes being authorized. Prevent DoS, spoofing, data integrity and other router security issues by blocking router source MAC and router source IP addresses at the edge.
SMTP/POP Server Protocols Prevent data theft and worm propagation by blocking SMTP at the edge.
SNMP Protocol Only approved management stations or management data collection points need to be speaking SNMP. Prevent unauthorized users from using SNMP to view, read, or write management information.
FTP and TFTP Server Protocols Ensure file transfers and firmware upgrades are only originating from authorized file and configuration management servers.
Web Server Protocol Stop malicious proxies and application-layer attacks by ensuring only the right Web servers can connect from the right location at the right time, by blocking HTTP on the source port for this device.
Legacy Protocols If IPX, AppleTalk, DECnet or other protocols should no longer be running on your network, prevent clients from using them. Some organizations even take the approach that unless a protocol is specifically allowed, all others are denied.