Cisco Express Forwarding
MPLS relies on Cisco Express Forwarding (CEF) to indicate the next hop for a packet to use. Cisco routers can use three types of packet switching Process switching The CPU must be interrupted and a route table lookup done for every packet. This is the slowest type of switching. Fast switching A route table lookup is done only for the first packet in a flow. The next-hop information, including the Layer 2 header, is cached and used for the remainder of the packets in the flow. Faster than...
Configuring a Crypto
A crypto map pulls together the transform sets and crypto ACLs and associates them with a remote peer. A sequence number can be used when configuring a crypto map. Multiple crypto maps with the same name but different sequence numbers form a crypto map set. Traffic is evaluated against each crypto map depending on its sequence number to see whether it should be protected. This permits more complex and granular traffic filtering. The following example shows a crypto map that links the transform...
Applying the Crypto Map to an Interface
After the crypto map has been configured, it must be applied to an interface for it to take effect. It is applied at the outgoing interface the one that VPN traffic will use to reach the other end of the VPN. You might need to use a static route or otherwise adjust your routing to force traffic bound for the VPN destination networks to use the correct outgoing interface. The following example shows the crypto map TO_SERVERS applied to c interface serial 0 0 0. Note that the router replies with...
Adsl
ADSL is a popular residential service because it can carry both voice and data over one twisted pair of wires. This capability is accomplished by using either a splitter or a filter. A splitter takes the incoming analog signals and splits off the frequencies under 4 MHz to a voice line. It sends all other traffic to the DSL line. Splitters are more typically used at the CO than the subscriber premises because they require a technician to install them. A filter, or microfilter, requires no...
Troubleshooting ADSL
When troubleshooting ADSL problems, start with checking Layer 1 physical connectivity. If that checks out okay, progress to checking Layer 2 connectivity. Finally, check Layer 3. Try the following procedures when troubleshooting DSL physical layer problems 1. Check for the carrier detect light on the router's ATM interface. If it is off, use the show interfaces atm interface_number command to check the interface status. If the interface status is down, try swapping out the RJ-11 cable...
EIGRP Route Selection
An EIGRP router receives advertisements from each neighbor that lists the advertised distance (AD) and feasible distance (FD) to a route. The AD is the metric from the neighbor to the network. FD is the metric from this router, through the neighbor, to the network. The EIGRP metric is shown in Figure 2-1. nc 1 107 k 2 x BWmin ,, k5 metric 256(k1 x-+-shl + k3 x > delays)(-) BWmin 256 - load reliability + k4 The k values are constants. Their default values are k1 1, k2 0, k3 1, k4 0, and k5 0....
MAC Address Flooding
In a MAC address flooding attack, the attacker fills the switch's Content Addressable Memory (CAM) table with invalid MAC addresses. After the table is full, all traffic with an address not in the table is flooded out all interfaces. This has two bad effects more traffic on the LAN and more work for the switch. Additionally, the intruder's traffic is also flooded, so they have access to more ports than they would normally have. After the attack stops, CAM entries age out and life returns to...
Configuring PPPoE CPE
The following tasks must be completed to configure a CPE router with for PPPoE 1. Configure the internal and external interfaces. 2. Configure a dialer interface. 4. Configure the router to act as a DHCP server. First, configure the internal Ethernet interface with an IP address. It will be the default gateway for the users. Also, configure it as the inside interface for NAT. Do not put an IP address on the external Ethernet interface. Enable PPPoE on it, and assign it to a PPPoE client dialer...
Classifying and Marking in a VoIP Network
Figure 4-2 shows what happens to the CoS and DSCP settings of a data packet as it moves through a QoS-enabled LAN. Figure 4-2 CoS and DSCP Changes for a Data Packet Data DSCP 56 CoS 7 IP Header 802.1p bits PC with 802.1Q-capable NIC sends a packet through the phone. PC user sets the packet's DSCP to 56 (IP precedence 7) and CoS to 7. traffic to 0 before forwarding to Access switch. Does not change the DSCP value. Switch is configured classify and mark data traffic. It sets both DSCP and CoS on...
Wireless LAN Overview
Devices on a wireless LAN (WLAN) transmit and receive data using radio or infrared signals, sent through an access point (AP). WLANs function similarly to Ethernet LANs with the access point providing connectivity to the rest of the network as would a hub or switch. WLANs use an Institute of Electrical and Electronics Engineers (IEEE) standard that defines the physical and data link specifications, including the use of Media Access Control (MAC) addresses. The same protocols (such as IP) and...
