An AS is multihomed if it has more than one exit point to the outside world. An AS can be multihomed to a single provider or multiple providers. A nontransit AS does not allow transit traffic to go through it. Transit traffic is any traffic that has a source and destination outside the AS. Figure 4-5 illustrates an AS (AS1) that is nontransit and multihomed to two providers, ISP1 and ISP2. Figure 4-5. Multihomed Nontransit AS Example A nontransit AS would only advertis..
802.11 Physical Layer Standards
A wireless LAN enables mobile, portable, and stationary devices to easily communicate with each other within an enterprise facility and throughout a campus environment. For example, retail stores have been using wireless LANs since the early 1990s to enable wireless bar code scanning when performing price marking and inventory applications. Despite the relatively high cost for wireless LAN components at that time, the retail stores were still able to achieve significant retur..
Smurf Attacks, Directed Broadcasts, and RPF Checks
A smurf attack occurs when a host sends a large number of ICMP Echo Requests with some atypical IP addresses in the packet. The destination address is a subnet broadcast address, also known as a directed broadcast address. Routers forward these packets based on normal matching of the IP routing table, until the packet reaches a router connected to the destination subnet. This final router then forwards the packet onto the LAN as a LAN broadcast, sending a copy to every device..
The initial Layer 3 switching engine for the Catalyst 6000 family consisted of the Multi-layer Switch Model (MSM). Based on Catalyst 8510 technology, the MSM provides a router-on-a-stick configuration integrated into the Catalyst 6000 chassis. Therefore, the MSM brings the power of the 8510 to the Catalyst 6000 family (namely IP and IPX routing at approximately 5 million packets per second [mpps]). Note The MSM contains a faster CPU that is currently used in the 8510. From..
The Inter-Switch Link (ISL) protocol is a Cisco-proprietary method for preserving the source VLAN identification of frames passing over a trunk link. ISL performs frame identification in Layer 2 by encapsulating each frame between a header and a trailer. Any Cisco switch or router device configured for ISL can process and understand the ISL VLAN information. ISL primarily is used for Ethernet media, although Cisco has included provisions to carry Token Ring, FDDI, and ATM fra..
