Tag Archives: 5.2a

5.2.a Implement and troubleshoot switch security features

5.2.a [i] VACL, PACL

VLAN ACLs (VACLs) can provide access control for all packets that are bridged within a VLAN or that are routed into or out of a VLAN or a WAN interface for VACL capture. Unlike Cisco IOS ACLs that are applied on routed packets only, VACLs apply to all packets and can be applied to any VLAN or WAN interface. VACLs are processed in the ACL TCAM hardware. VACLs ignore any Cisco IOS ACL fields that are not supported in hardware.

You can configure VACLs for IP and MAC-layer traffic. VACLs applied to WAN interfaces support only IP traffic for VACL capture. If a VACL is configured for a packet type, and a packet of that type does not match the VACL, the default action is to deny the packet.

The port ACL (PACL) feature provides the ability to perform access control on specific Layer 2 ports. A Layer 2 port is a physical LAN or trunk port that belongs to a VLAN . Port ACLs are applied only on the ingress traffic. The port ACL feature is supported only in hardware (port ACLs are not applied to any packets routed in software). They apply to both voice and data VLANs. When you create a port ACL, an entry is created in the ACL TCAM. You can use the show tcam counts command to see how much TCAM space is available. The PACL feature does not affect Layer 2 control packets received on the port. You can use the access-group mode command to change the way that PACLs interact with other ACLs. PACLs use the following modes:

Prefer port mode—If a PACL is configured on a Layer 2 interface, the PACL takes effect and overwrites the effect of other ACLs (Cisco IOS ACL and VACL). If no PACL feature is configured on the Layer 2 interface, other features applicable to the interface are merged and are applied on the interface.

Merge mode—In this mode, the PACL, VACL, and Cisco IOS ACLs are merged in the ingress direction following the logical serial. This is the default access group mode.

You configure the access-group mode command on each interface . The default is merge mode.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 5181-5184).  . Kindle Edition.


5.2.a Implement and troubleshoot switch security features

5.2.a [ii] Stormcontrol

A traffic storm occurs when packets flood the LAN, creating excessive traffic and degrading network performance. The traffic storm control feature prevents LAN ports from being disrupted by a broadcast, multicast, or unicast traffic storm on physical interfaces. Traffic storm control (also called traffic suppression) monitors incoming traffic levels over a 1-second traffic storm control interval , and during the interval it compares the traffic level with the traffic storm control level that you configure. The traffic storm control level is a percentage of the total available bandwidth of the port. Each port has a single traffic storm control level that is used for all types of traffic (broadcast, multicast, and unicast).

Traffic storm control monitors the level of each traffic type for which you enable traffic storm control in 1-second traffic storm control intervals.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 5188-5193).  . Kindle Edition.


5.2.a Implement and troubleshoot switch security features

5.2.a [iii] DHCP snooping

DHCP snooping is a security feature that acts like a firewall between untrusted hosts and trusted DHCP servers. The DHCP snooping feature performs the following activities:

● Validates DHCP messages received from untrusted sources and filters out invalid messages.

● Rate-limits DHCP traffic from trusted and untrusted sources.

● Builds and maintains the DHCP snooping binding database, which contains information about untrusted hosts with leased IP addresses.

● Utilizes the DHCP snooping binding database to validate subsequent requests from untrusted hosts.

● Other security features, such as dynamic ARP inspection (DAI), also use information stored in the DHCP snooping binding database.

DHCP snooping is enabled on a per-VLAN basis. By default, the feature is inactive on all VLANs. You can enable the feature on a single VLAN or a range of VLANs. The DHCP snooping feature is implemented in software on the route processor (RP). Therefore, all DHCP messages for enabled VLANs are intercepted in the Policy Feature Card (PFC) and directed to the RP for processing.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 5201-5209).  . Kindle Edition.


5.2.a Implement and troubleshoot switch security features

5.2.a [iv] IP source-guard

IP source guard provides source IP address filtering on a Layer 2 port to prevent a malicious host from impersonating a legitimate host by assuming the legitimate host’s IP address. The feature uses dynamic DHCP snooping and static IP source binding to match IP addresses to hosts on untrusted Layer 2 access ports.

Initially, all IP traffic on the protected port is blocked except for DHCP packets. After a client receives an IP address from the DHCP server, or after static IP source binding is configured by the administrator, all traffic with that IP source address is permitted from that client. Traffic from other hosts is denied. This filtering limits a host’s ability to attack the network by claiming a neighbor host’s IP address . IP source guard is a port-based feature that automatically creates an implicit port access control list (PACL).

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 5214-5217).  . Kindle Edition.



5.2.a Implement and troubleshoot switch security features

5.2.a [v] Dynamic ARP inspection

ARP spoofing attacks and ARP cache poisoning can occur because ARP allows a gratuitous reply from a host even if an ARP request was not received. After the attack, all traffic from the device under attack flows through the attacker’s computer and then to the router, switch, or host. An ARP spoofing attack can target hosts, switches, and routers connected to your Layer 2 network by poisoning the ARP caches of systems connected to the subnet and by intercepting traffic intended for other hosts on the subnet

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Location 5224).  . Kindle Edition. .