ACCESS CONTROL LIST

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• For protecting routers, Layer 3 forwarding (IP routing), and the layer 3 control plane(routing protocols), additionally RFCs 2827 & 3704 outline other types of protections
• RFC 2827 addresses issues with
• the use of the IP source & destination fields in the IP header to form some kind of attack
• RFC 3704 details some issues related to how the tools of 2827 may be best deployed over the internet.
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KEY LAYER 3 SECURITY recommendations from SAFE blueprint

• Using Secure Shell, enable secure telnet access to a router user interface.
• Enable SNMP security, particularly  adding SNMPv3 support
• Turn off all unnecessary servieces on the router platform
• Turn on logging to provide an audit trail
• Enable routing protocol authentication
• Enable the CEF forwarding path to avoid using flow-based paths like fast switching

General Layer 2 Security Recommendatinos

• Put unused switch ports in an unused VLAN & not use the VLAN 1.
• Native VLANs are not use on trunks.
• Reason is, an attacker on an access port might be able to hop from its access port VLAN to a trunk's native VLAN by sending frames that begin with multiple 802.1Q header.
• Cisco suggest using a different native VLAN for each trunk.
• Private VLANs restrict hosts on some ports from sending frames directly to each other.
• Private VLANs are created with some number of selected ports in the primary VLAN, with other isolated & community ports in one or more secondary VLANs.
• Isolated ports can send frames only to selected ports, and community ports can send frames to selected ports & other community ports in the same 2ry VLAN.
• Private VLANs could be applied generally for better security by making user ports isolated,
• They only allowing them access to ports like routers, servers or other network services.
• However, DHCP snooping, DAI & IP source gaurd are typically better choices
• Attackers uses the default gateway to overcome security provided by PVlans,
• to solve this router simply need inbound ACL, that denies traffic whose source & destination ip address are in the same local connected subnet.

Storm Control

• Catalyst switches need rate-limiting traffic at layer-2
• To do this uses the storm-control commands.
• Storm control configured to set min & max port traffic (unicast, multicast & broadcast).
• Each rate limit can be configured on a per-port basis.
• Storm control can be configured on each type of traffic based on
• Either packet rate or a percentage of the interface bandwidth.
• We can also specify rising & falling thresholds for each traffic type.
• If we don't specify falling threshold or if the falling threshold is the same as the rising threshold
• the switch port forward all traffic up to the configured limit 
• and will not wait for the specified falling threshold before forwarding it again.
• When any of the configured threshold is passed, the switch can take 3 additional actions (also on port basis)
• 1st & default is the switch can rate-limit by discarding excess traffic according to the configured commands & take no further action.
• The other 2 actions include performing the rate-limiting function & either shutting down the port or sending an SNMP trap.
• Commands
• interface f0/0
• storm-control broadcast level pps 100 50
• limit broadcast traffic to 100packets per seconds
• when traffic drops back to 50 pack/sec, begin forwarding traffic again.
• storm-control multicast level 0.50 0.40
• limit multicast traffic to 0.5 percent of the 100Mbps interface rate
• when traffic drops back to 400kbps, begin forwarding again
• storm-control action trap
• any of above conditions occure & results in rate-limiting, send an SNMP trap.
• show storm-control f0/0 {unicast | multicast \ broadcast }
• Limitation:
• it supports only physical ports
• storm control configure on etherchannel interface, but it has no effect.
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