Search Engine Traffic Guide
In addition to inadvertent misconfigurations, the problem of RTFM often rears its head. For a definition of RTFM, consult your friendly neighborhood search engine. The basics of the problem are this if the individual responsible for deploying a technology doesn't know much about the technology, the chances of it working as intended decrease significantly. As a result, it is critical that organizations set aside part of the budget to allocate for employee training.
A multiplexer is a physical-layer device that combines multiple data streams into one or more output channels at the source. Multiplexers demultiplex the channels into multiple data streams at the remote end and thus maximize the use of the bandwidth of the physical medium by enabling it to be shared by multiple traffic sources.
Before you spend too much time troubleshooting agent configuration, make sure that basic network communications are taking place. Again, follow the same basic troubleshooting procedures for CSA as for any other network application. These tools are available for almost every operating system and run on even the oldest hosts, making them quite popular. Simply search for the applications with your favorite search engine to obtain these tools.
So that you have a better understanding of a man-in-the-middle attack, I'll use Figure 2-5 to illustrate how this attack occurs. In this example, PeerA wants to send data to PeerB. PeerA does a DNS lookup for PeerB's address, shown in Step 1. However, the attacker also sees the DNS request and sends a reply back to PeerA before the DNS server has a chance, shown in Steps 2 and 3. The IP address that the attacker sends is the attacker's own IP address. PeerA knows no better and assumes that when it uses the IP address in the DNS reply that it is sending traffic to PeerB however, as shown in Step 4, the traffic actually is directed to the attacker.
There is something interesting about the last entry (*, 126.96.36.199), which is the Data-MDT for EuPoBank. No C flag is present, which indicates that no mVRF is connected. This is because the Paris PE router is sending traffic to this tunnel from its connected source the PE router is not receiving traffic from the tunnel. The Paris PE router is the root of the (*, 188.8.131.52) entry only.
The size of an enterprise network drives the design and placement of certain types of devices. If the network is designed according to the ECNM, there will be distinct devices separating the access, distribution, and backbone areas of the network. The network design and the types of applications supported will determine where certain traffic sources are located. In the case of multicast and IP telephony applications, they do share some common traffic types. Specifically, if a Cisco CallManager is providing music on hold, it may need to multicast that traffic stream.
Network simulation has at least two distinct realizations. The first models the network using software to emulate the traffic sources and sinks (drop offs), network devices, and the links that connect them. By varying model parameters, the designer can approximate the impact of more or less traffic demand or network resources. Although simulation software is expensive, for a large network it is far less expensive than building a flawed design. The second kind of simulation uses special hardware and software to generate traffic for injection into a live network for subsequent traffic analysis.
For interfaces configured to use Resource Reservation Protocol (RSVP), WRED chooses packets from other flows to drop rather than the RSVP flows. Also, IP precedence or DSCP helps determine which packets are dropped, because traffic at a lower priority has a higher drop rate than traffic at a higher priority (and, therefore, lower-priority traffic is more likely to be throttled back). In addition, WRED statistically drops more packets from large users than from small users. The traffic sources that generate the most traffic are more likely to be slowed down than traffic sources that generate little traffic.
An AAL 3 4 SAR PDU header consists of Type, Sequence Number, and Multiplexing Identifier fields. Type fields identify whether a cell is the beginning, continuation, or end of a message. Sequence number fields identify the order in which cells should be reassembled. The Multiplexing Identifier field determines which cells from different traffic sources are interleaved on the same virtual circuit connection (VCC) so that the correct cells are reassembled at the destination.
Arriving packets that find sufficient tokens available are said to conform. The appropriate number of tokens is removed from the bucket, and the specified conform action is executed. Traffic exceeding the normal burst limit, but falling within the excess burst limit, is handled via a RED-like managed discard policy that provides a gradual effect for the rate limit and allows the traffic sources to slow down before suffering sequential packet discards.
Hopefully this simple scenario has shown you the power of the details provided by IDS-enabled devices, the ease of using these devices, and the powerful search engines available at Cisco.com. The error messages are somewhat intuitive and if you come across a difficult question in the exam make sure you apply a commonsense approach. Obviously you will not have Internet access during the exam, so it is safe to assume Cisco will not test your knowledge of every obscure signature or scenario out there, but some common examples are presented in this simple scenario.
The AS_PATH access list uses a powerful text-parsing tool known as regular expressions, or regex for short. Regular expressions are commonly used in such programming languages as Perl, Expect, awk, and Tel, in search engines, and in UNIX utilities such as egrep. Regular expressions use a string of characters, all of which are either metacharacters or literals, to find matches in text. In the case of AS_PATH access lists, they are used to find matches in the AS JPATH attributes of BGP updates.
In addition to allocating sufficient time for a baseline analysis, it is also important to find a typical time period to do the analysis. A baseline of normal performance should not include nontypical problems caused by exceptionally large traffic loads. For example, at some companies, end-of-the quarter sales processing puts an abnormal load on the network. In a retail environment, network traffic can increase fivefold around Christmas time. Network traffic to a web server can unexpectedly increase tenfold if the website gets linked to other popular sites or listed in search engines.
The previous scenarios send the more-specific routes of AS 100 to AS 200 so that AS 200 can implement routing policy. That is, AS 200 uses the routes to set routing preferences for sending traffic to AS 100. AS 100 also can influence its incoming traffic by manipulating its outgoing advertisements. For example, advertising 192.168.193.0 24 over the Stowe Sugarbush link and not over the Mammoth Diamond link causes incoming traffic to use the Stowe Sugarbush link. An administrator might want to implement such a policy if the AS is geographically diverse. For instance, Stowe might be in Vermont and Mammoth in California. The administrator might want incoming traffic to use the ingress point closest to the destination, to minimize internal routing.
In either case, IBNS operates at the edge of the network on access ports. When a device is plugged into the network, Layers 1 and 2 are established, but before access to the network is permitted, the access switch challenges the device to provide its identity credentials. The credentials provided by the device are passed through the network to authentication servers in the data center and are validated. Validated devices are granted access, and unauthorized devices are prevented from sending traffic to the network.
3 Networks 192.168.1.0, 192.168.2.0, 192.168.3.0, 192.168.4.0, and 192.168.5.0 exisi within AS 2. The administrator of this AS wants the neighboring AS to prefer R5 when sending traffic to 192.168.1.0 and 192.168.3.0. The neighboring AS should prefer R6 when sending traffic to 192.168.2.0 and 192.168.4.0. In each case, the less-preferred link serves as a backup to the more-preferred link. 192.168.5.0 is a private network and must not be advertised to any EBGP peer. Modify the configurations written in Exercise 2 to implement this policy.
By definition, IDS and IPS solutions incorporate signatures that trigger based on information that is located throughout the packet. Inline deep-packet inspection refers to the ability to perform actual protocol analysis on network traffic. Many applications (including malicious programs) attempt to use open ports to pass information through access control lists on your network. Using inline deeppacket inspection enables you to enforce your security policy beyond basic port numbers. For instance, this functionality enables you to prevent attackers (and applications) from sending traffic to or from port 80 unless the traffic is legitimate HTTP traffic.
ISL trunk encapsulation is designed for trunking over a point-to-point connection between two Catalysts using Ethernet. Only two Catalysts connect to the link. This contrasts with connectivity over an FDDI system. FDDI operates as a shared network media (half duplex) and can have more than two participants on the network. A different encapsulation scheme, therefore, is used when trunking over an FDDI network. Cisco adapted an IEEE standard for secure bridging over an 802-based network and applied it to FDDI trunking between Catalysts. IEEE 802.10 devised the standard to facilitate the transport of multiple traffic sources over shared local and metropolitan networks and yet retain logical isolation between the source networks at the receiver.
Documenting traffic flow involves identifying and characterizing individual traffic flows between traffic sources and stores. Traffic flows have recently become a hot topic for discussion in the Internet community. A lot of progress is being made on defining flows, measuring flow behavior, and allowing an end station to specify performance requirements for flows.
Attackers can attempt to launch an attack by sending gratuitous ARP (GARP) replies. These GARP messages can tell network devices that the attacker's MAC address corresponds to specific IP addresses. For example, the attacker might be able to convince a PC that the attacker's MAC address is the MAC address of the PC's default gateway. As a result, the PC starts sending traffic to the attacker. The attacker captures the traffic and then forwards the traffic to the appropriate default gateway.
The default-information originate command is used with level 2 routers for sending traffic to destinations not found in the local routing table. This command is used to send a default route in the backbone, and it creates an external entry into the L2 LSP. Unlike OSPF, this command does not require a default route to be present in the router that is originating the default route.
The fundamental problem that service providers face today when offering native multicast services to end customens is the amount of multicast distribution information (that is S, G or *, G states) that needs to be maintained to provide the most optimal multicast traffic distribut ion. When a mul ticast s ource becomes active within a particular customer site, the multicast eraffic mupt Oravel through the service provider network to reach all PE routers that have receivers connected to CE routers for that multicast group. To prevent unnecessary traffic delivery, the service provider must avoid sending traffic to PE routers that have no interested receivers. To accomplish this goal and achieve optimal routing, each P router in the network must maintain state information for all active customer distribution trees.
This chapter describes techniques for characterizing traffic flow, traffic volume, and protocol behavior. The techniques include recognizing traffic sources and data stores, documenting application and protocol usage, and evaluating network traffic caused by common protocols. Upon completion of this chapter, you will be able to analyze network traffic patterns to help you select appropriate logical and physical network design solutions to meet a customer's goals.
In multicast forwarding, the source is sending traffic to an arbitrary group of hosts that is represented by a multicast group address. The multicast router must determine which direction is the upstream direction (toward the source) and which one is the downstream direction (or directions). If there are multiple downstream paths, the router replicates the packet and forwards it down the appropriate downstream paths (best unicast route metric), which is not necessarily all paths.
Very few people predicted the coming of the Internet. After all, it was not real-time voice or video that stole the show, but the ubiquity of home personal computers coupled with a few applications. These included the simple one-to-one or one-to-many communication applications, such as email and chat groups, and the powerful Web browsers and Internet search engines that turned the Internet into a virtual world in which people could journey, learn, teach, and share. Users did not need megabits per second to enter this world 32 Kbps was happiness, 64 Kbps was bliss, and 128 Kbps was heaven.
Agilent's RouterTester is a powerful and flexible test system for generating traffic streams and testing network design and routing scalability. The RouterTester system can generate IPv4 and IPv6 routing, signaling, multicast, and tunneling protocol traffic over a wide range of Packet over SONET (POS), ATM, and Ethernet interfaces. It has the capability of handling up to 2000 individual streams per port. It also includes tools for sending realistic traffic streams, building large test configurations, performing QoS and performance measurements, and verifying correct protocol implementation.
With Option 82 enabled, the DHCP server can use the extra information to assign IP addresses, perform access control, and set quality of service (QoS) and security policies (or other parameter-assignment policies) for each DHCP client. When the server returns a response, it also includes Option-82 information. Not all DHCP servers support Option 82, however. At the time of this writing, a Google search for DHCP server option 82 returned just a few hits, among which Cisco Network Registrar and Avaya's server figured. Moreover, the DHCP server developed by Internet Systems Consortium (ISC) can log Option 82, which is called agent.circuit-id.
First, look at the case of Host-A sending traffic to Host-B. The traffic from Host-A to the router travels up the ISL links connecting the Catalysts and the router to each other. As the first packet hits the NFFC in each Catalyst, it is recognized as a candidate packet and three partial shortcut entries are created (one per Catalyst). As the packet travels back down from the router to reach Host-B, all three NFFC cards
Lastly, you can access the CLI through Telnet over the network. The Catalyst has an internal logical interface, sc0,that you can assign an IP address to. This address becomes the source address when generating traffic in the Catalyst, or the destination address when you attempt to reach the Catalyst. Assigning an address to this logical interface causes the Catalyst to act like an IP end station on the network. You can use the address to perform Telnet, TFTP, BOOTP, RARP, ICMP, trace, and a host of other end station functions.
Searches can be performed on a single group of words or phrases. Groups of words must be seperated by a comma (,). This works similar to an AND function in the search engine. For example, let's say you type 7000,memory This will tell the search engine to look for the words 7000 AND memory , regardless of where they occur in a document. However, if you type 7000 memory This will be interpreted as a phrase. The search engine will then look for the phrase 7000 memory . If these words are contained in a document but do not appear together, the document will not be found in this type of search. The search engine can accept a rich set of commands, although in most cases, the examples provided above will suffice. The search engine will also accept boolean commands such as AND and OR. These must be enclosed in angle brackets For example 2500 RSRB The search engine can also interpret stemming. Stemming is defined by using a single quote. This and the search engine will search for words...
Amultiplexer is a physical layer device that combines multiple data streams into one or more output channels at the source. Multiplexers demultiplex the channels into multiple data streams at the remote end and thus maximize the use of the bandwidth of the physical medium by enabling it to be shared by multiple traffic sources.
The name captured the essence of the group and the essence of the times we live in, where the Internet and the services it enables provides a foundation for communication. If we are to be precise, we must highlight the fact that the Internet cannot, however, be equated to one of its search engines alone this is just another minor misnomer, typical in the case of popular technologies. The Internet is much more than a search engine, and even in the middle of nowhere, the Internet and its various manifestations are a major element in our thoughts and our vocabulary.
Various Internet sites, too many to mention here, provide tuition and virtual labs. (These labs are called virtual but, in fact, are real Cisco devices.) You can hire and actually configure Cisco IOS routers and switches for a set fee. Point your search engine toward the keywords, Cisco virtual labs. Cisco provides an excellent product called Cisco Interactive Mentor (CIM). CIM is a virtual IOS simulator that enables you to configure a set number of IOS features without having to purchase expensive Cisco routers.
CiscoWorks includes several web-based solutions targeted at configuring, monitoring, and troubleshooting LAN and WAN environments. Go to a search engine such as Google and search for ciscoworks, which should bring you to Cisco.com to help you understand, monitor, and react to problems.
Data scavenging is generally step 1 in any deliberate attack against a network. Here, the attacker uses a combination of network-based utilities and Internet search engine queries to learn as much as possible about the target company. The attack is almost impossible to detect for two main reasons The information gained through Whois, Nslookup, or Internet search engines is usually public information that can be learned by anyone. Oftentimes, the information gained by the attacker comes from servers other than the victim's servers (as is the case with Whois queries). Using an Internet search engine can yield all sorts of good information as well. After a successful data-scavenging attack, the attacker might know the following about the victim network
The Web has many excellent sources of information. Readers are encouraged to conduct their own Internet searches. Just try a Google search on terms such as network management, command-line interface, SNMP, and service-level management. Searches on the various topics discussed in this book are sure to yield a wealth of information, as are the websites of vendors engaged in management technology. Here is a very short list of links that you may want to try.
The access router can be configured to apply policy based on access lists. At the same time, various CAR rate-limit policies can be applied. This approach is static the customers are not allowed the flexibility of adjusting the level of service that they wish to have applied to various traffic sources.
The second tactic that attackers employ is making the network device generate large volumes of packets. They do this by sending traffic to the network device, to the location on the device where the CPU is expected to process and generate certain responses to specific requests. An example is sending malformed packets and making the network device send ICMP unreachable messages.
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