MPLS Architecture The Building Blocks
As with any new technology, several new terms are introduced to describe the devices that make up the architecture. These new terms describe the functionality of each device and their roles within the MPLS domain structure. The first device to be introduced is the Label Switch Router (LSR). Any router or switch that implements label distribution procedures and can forward packets based on labels falls under this category. The basic function of label distribution procedures is to allow an LSR to...
Router Port Group Management Protocol
RGMP is a Layer 2 protocol that enables a router to communicate to a switch which multicast group traffic the router does and does not want to receive from the switch. By being able to restrict the multicast destinations that a switch forwards to a router, a router can reduce its overhead. In fact, RGMP was designed to help routers reduce overhead when they are attached to high-speed LAN backbones. Although RGMP is Cisco proprietary, oddly enough it cannot work concurrently with...
RIP Offset Lists
RIP offset lists allow RIP to add to a route's metric, either before sending an update, or for routes received in an update. The offset list refers to an ACL (standard, extended, or named) to match the routes any matched routes have the specified offset, or extra metric, added to their metrics. Any routes not matched by the offset list are unchanged. The offset list also specifies which routing updates to examine by referring to a direction (in or out) and, optionally, an interface. If the...
IP Prefix Lists
IP prefix lists provide mechanisms to match two components of an IP route The route prefix (the subnet number) The prefix length (the subnet mask) The redistribute command cannot directly reference a prefix list, but a route map can refer to a prefix list by using the match command. A prefix list itself has similar characteristics to a route map. The list consists of one or more statements with the same text name. Each statement has a sequence number to allow deletion of individual commands,...
Switching and Bridging Logic
In this chapter so far, you have been reminded about the cabling details for Ethernet along with the formats and meanings of the fields inside Ethernet frames. A switch's ultimate goal is to deliver those frames to the appropriate destination(s) based on the destination MAC address in the frame header. Table 1-7 summarizes the logic used by switches when forwarding frames, which differs based on the type of destination Ethernet address and on whether the destination address has been added to...
Time Exceeded ICMP Message
The ICMP Time Exceeded message notifies a host when a packet it sent has been discarded because it was out of time. Packets are not actually timed, but to prevent packets from being forwarded forever when there is a routing loop, each IP packet header includes a Time to Live (TTL) field. Routers decrement TTL by 1 every time they forward a packet if a router happens to decrement TTL of a packet to 0, the router discards the packet and sends an ICMP Time Exceeded message to the sender of the...
IP Access Control List Review
A relatively deep knowledge of IP ACL configuration and use is assumed to be pre-requisite knowledge for readers of this book. In fact, many of the examples in the earlier sections of the book did not take the space required to explain the detailed logic of ACLs used in the examples. However, some reference information, as well as statements regarding some of the rules and practices regarding IP ACLs, is useful for general CCIE Routing and Switching exam study. Those details are presented in...
Foundation Summary
This section lists additional details and facts to round out the coverage of the topics in this chapter. Unlike most of the Cisco Press Exam Certification Guides, this book does not repeat information presented in the Foundation Topics section of the chapter. Please take the time to read and study the details in the Foundation Topics section of the chapter, as well as review the items in the Foundation Topics section noted with a Key Point icon. Table 1-8 lists the different types of Ethernet...
Port Channels
When a network design includes multiple parallel segments between the same pair of switches, one switch ends up in a forwarding state on all the links, but the other switch blocks all but one of the ports of those parallel segments. As a result, only one of the links can be used at any point in time. Using Fast EtherChannel (FEC) (using FastE segments) and Gigabit EtherChannel (GEC) (using GigE segments) allows the combined links to be treated as one link from an STP perspective, so that all...
Ethernet Layer 2 Framing and Addressing
In this book, as in many Cisco courses and documents, the word frame refers to the bits and bytes that include the Layer 2 header and trailer, along with the data encapsulated by that header and trailer. The term packet is most often used to describe the Layer 3 header and data, without a Layer 2 header or trailer. Ethernet's Layer 2 specifications relate to the creation, forwarding, reception, and interpretation of Ethernet frames. The original Ethernet specifications were owned by the...
Class Based Policing Configuration
CB Policing uses the familiar MQC commands for configuration. As a result, a policy map can police all packets using the convenient class-default class, or it can separate traffic into classes, apply different policing parameters to different classes of traffic, or even simply not police some classes. The police command configures CB Policing inside a policy map. On the police command, you define the policing rate in bps, the Bc in bytes, and the Be in bytes, along with the actions for each...
Frame Relay Congestion De Becn and FECN
FR networks, like any other multiaccess network, create the possibility for congestion caused by speed mismatches. For instance, imagine an FR network with 20 remote sites with 256-kbps links, and one main site with a T1 link. If all 20 remote sites were to send continuous frames to the main site at the same time, about 5 Mbps of data would need to exit the FR switch over the 1.5-Mbps T1 connected to the main router, causing the output queue on the FR switch to grow. Similarly, when the main...
VLSM Subnet Allocation
So far in this chapter, most of the discussion has been about examining existing addresses and subnets. Before deploying new networks, or new parts of a network, you must give some thought to the ranges of IP addresses to be allocated. Also, when assigning subnets for different locations, you should assign the subnets with thought for how routes could then be summarized. This section covers some of the key concepts related to subnet allocation and summarization. (This section focuses on the...
Adding iBGP Routes to the IP Routing Table
Cisco IOS has the same two requirements for adding iBGP routes to the IP routing table as it does for eBGP routes The route must be the best BGP route. The route must be the best route (according to the AD) in comparison with other routing Additionally, for iBGP-learned routes, IOS considers the concept of BGP synchronization. With BGP synchronization (often called sync) disabled using the no synchronization command, BGP uses the same logic for iBGP routes as it does for eBGP routes regarding...
Basic Switch Port Configuration
The three key configuration elements on a Cisco switch port are auto-negotiation, speed, and duplex. Cisco switches use auto-negotiation by default it is then disabled if both the speed and duplex are manually configured. You can set the speed using the speed auto 10 100 1000 interface subcommand, assuming the interface supports multiple speeds. You configure the duplex setting using the duplex auto half full interface subcommand. Example 1-1 shows the manual configuration of the speed and...
Do I Know This Already Quiz
Table 24-1 outlines the major headings in this chapter and the corresponding Do I Know This Already quiz questions. Table 24-1 Do I Know This Already Foundation Topics Section-to-Question Mapping Table 24-1 Do I Know This Already Foundation Topics Section-to-Question Mapping In order to best use this pre-chapter assessment, remember to score yourself strictly. You can find the answers in Appendix A, Answers to the 'Do I Know This Already ' Quizzes. 1. The TCP software on PC1 uses IP on PC1 to...
STP Configuration and Analysis
Example 3-1, based on Figure 3-6, shows some of the basic STP configuration and show commands. Take care to note that many of the upcoming commands allow the parameters to be set for all VLANs by omitting the VLAN parameter, or set per VLAN by including a VLAN parameter. Example 3-1 begins with SW1 coincidentally becoming the Root switch. After that, SW2 is configured to become root, and SW3 changes its Root Port as a result of a configured port cost in VLAN 1. Figure 3-6 Network Used with...
Default Routes
Routers forward packets using a default route when there are no specific routes that match a packet's destination IP address in the IP routing table. Routing protocols can advertise default routes, with each router choosing the best default route to list as that router's gateway of last resort. This section covers how a router can create a default route and then cause an IGP to advertise the default route. In addition to the advertisement of default routes, each router may use one of two...
QinQ Tunneling
Traditionally, VLANs have not extended beyond the WAN boundary. VLANs in one campus extend to a WAN edge router, but VLAN protocols are not used on the WAN. Today, several emerging alternatives exist for the passage of VLAN traffic across a WAN, including 802.1Q-in-Q, Ethernet over MPLS (EoMPLS), and VLAN MPLS (VMPLS). While these topics are more applicable to the CCIE Service Provider certification, you should at least know the concept of 802.1 Q-in-Q tunneling. Also known as Q-in-Q or Layer 2...
Weighted Fair Queuing
Weighted fair queuing differs from PQ and CQ in several significant ways. The most outwardly obvious difference is that WFQ does not allow classification options to be configured. WFQ automatically classifies packets based on flows, with each flow being placed into a separate queue. For WFQ purposes, a flow is defined as all packets with the same values for the following Transport layer protocol (TCP or UDP) TCP or UDP destination port Because WFQ puts packets of different flows in different...
ISL and 8021Q Configuration
Cisco switches use the Dynamic Trunk Protocol (DTP) to dynamically learn whether the device on the other end of the cable wants to perform trunking and, if so, which trunking protocol to use. DTP learns whether to trunk based on the DTP mode defined for an interface. Cisco switches default to use the DTP desirable mode, which means that the switch initiates sending DTP messages, hoping that the device on the other end of the segment replies with another DTP message. If a reply is received, DTP...
Designated Routers on WANs and OSPF Network Types
Using a DR makes good sense on a LAN because it improves LSA flooding efficiency. Likewise, not using a DR on a point-to-point WAN link also makes sense, because with only two routers on the subnet, there is no inefficiency upon which to improve. However, on nonbroadcast multiaccess (NBMA) networks, arguments can be made regarding whether a DR is helpful. So, OSPF includes several options that include a choice of whether to use a DR on WAN interfaces. Cisco router interfaces can be configured...
Class Based Marking CB Marking Configuration
As with the other QoS tools whose names begin with the phrase Class-Based, you will use MQC commands to configure CB Marking. The following list highlights the key points regarding CB Marking configuration and logic CB Marking requires CEF (enabled using the ip cef global command). Packets are classified based on the logic in MQC class maps. An MQC policy map refers to one or more class maps using the class class-map-name command packets classified into that class are then marked. CB Marking is...
Configuring Route Maps with the routemap Command
Route maps provide programming logic similar to the If Then Else logic seen in other programming languages. A single route map has one or more route-map commands in it, and routers process route-map commands in sequential order based on sequence numbers. Each route-map command has underlying matching parameters, configured with the aptly named match command. (To match all packets, the route-map clause simply omits the match command.) Each route-map command also has one or more optional set...
Route Summarization Concepts
The ability to recognize and define how to most efficiently summarize existing address ranges is an important skill on both the written and lab exams. For the written exam, the question may not be as straightforward as, What is the most efficient summarization of the following subnets Rather, the math required for such a question might simply be part of a larger question. Certainly, such math is required for the lab exam. This section looks at the math behind finding the best summarization...
IGMP Version
Figure 19-7 shows the 8-octet format of an IGMPvl message. Version 4-bit field that is always set to 1. Type 4-bit field that is either of two message types defined by IGMPvl Type 1, Host Membership Query Used only by routers. Type 2, Host Membership Report Used only by hosts. Unused 8-bit field that contains zeros when sent and is ignored when received. Checksum Carries the 16-bit checksum computed by the source for the IGMP message. The receiving device examines the checksum value, and if it...
MLS Configuration
The upcoming MLS configuration example is designed to show all of the configuration options. The network design is shown in Figures 7-4 and 7-5. In Figure 7-4, the physical topology is shown, with routed ports, VLAN trunks, a routed PortChannel, and access links. Figure 7-5 shows the same network, with a Layer 3 view of the subnets used in the network. Figure 7-4 Physical Topology Example Using MLS (T Trunk (also a switchport) (R Routed Port (T Trunk (also a switchport) (R Routed Port Figure...
Timers Used in IGMPvl and IGMPv2
Table 19-4 summarizes important timers used in IGMPvl and IGMPv2, their usage, and default values. Table 19-4 Important Timers Used in IGMPv1 andIGMPv2 Table 19-4 Important Timers Used in IGMPv1 andIGMPv2 A time period between General Queries sent by a router. The maximum response time for hosts to respond to the periodic general Queries. 10 seconds , can be between .1 and 25.5 seconds A time period during which if a router doesn't receive an IGMP Report, the router concludes that there are no...
IGMP Snooping
What happens if your network has non-Cisco switches You cannot use CGMP because it is Cisco proprietary. IGMP snooping can be used for a multivendor switched network to control distribution of multicast traffic at Layer 2. IGMP snooping requires the switch software to eavesdrop on the IGMP conversation between multicast hosts and the router. The switch examines IGMP messages and learns the location of multicast routers and group members. NOTE Many Cisco switches support IGMP snooping, including...
Private VLANs
Engineers may design VLANs with many goals in mind. In many cases today, devices end up in the same VLAN just based on the physical locations of the wiring drops. Security is another motivating factor in VLAN design devices in different VLANs do not overhear each other's broadcasts. Additionally, the separation of hosts into different VLANs and subnets requires an intervening router or multilayer switch between the subnets, and these types of devices typically provide more robust security...
Comparing Queuing Tools
Cisco IOS provides a wide variety of queuing tools. The upcoming sections of this chapter describe several different IOS queuing tools, with a brief summary ending the section on queuing. Table 15-2 summarizes the main characteristics of different queuing tools that you will want to keep in mind while comparing each successive queuing tool. Table 15-2 Key Comparison Points for Queuing Tools Table 15-2 Key Comparison Points for Queuing Tools The ability to look at packet headers to choose the...
Carrier Detect and Interface Resets
A router has visibility into T1 framing, along with the alarm conditions, but only if the serial card has a built-in CSU DSU. However, with an external CSU DSU, the router has no insight into the framing or encoding on the circuit. Instead, the router can sense the voltages on the various pins on the serial cable. Table 17-4 lists and describes the purpose of the five most important signaling pins in serial cables. (Note that in this model, the term data communications equipment DCE refers to...
Cisco Group Management Protocol
IGMP helps routers to determine how to distribute multicast traffic. However, IGMP works at Layer 3, and switches do not understand IGMP messages. Switches, by default, flood multicast traffic to all the hosts in a broadcast domain, which wastes bandwidth. Figure 19-16 illustrates the problem. Figure 19-16 Switches Flood Multicast Traffic Figure 19-16 Switches Flood Multicast Traffic -> - IGMP Join 226.6.6.6 -> - Multicast to 226.6.6.6 -> - IGMP Join 226.6.6.6 -> - Multicast to...
Building Adjacency Information ARP and Inverse ARP
The CEF adjacency table entries list an outgoing interface and a Layer 2 and Layer 3 address reachable via that interface. The table also includes the entire data link header that should be used to reach that next-hop (adjacent) device. The CEF adjacency table must be built based on the IP routing table, plus other sources. The IP routing table entries include the outgoing interfaces to use and the next-hop device's IP address. To complete the adjacency table entry for that next hop, the router...
Label Binding and Distribution
As soon as the Label Information Base (LIB) is created in a router, a label is assigned to every Forward Equivalence Class known to the router. For unicast destination-based routing, the FEC is equivalent to an IGP prefix in the IP routing table. Thus, a label is assigned to every prefix in the IP routing table and the mapping between the two is stored in the LIB. NOTE Labels are not assigned to BGP routes in the IP routing table. The BGP routes use the same label as the interior route toward...
The Mechanics of the redistribute Command
The redistribute router subcommand tells one routing protocol to take routes from another routing protocol. This command can simply redistribute all routes or, by using matching logic, redistribute only a subset of the routes. The redistribute command also supports actions for setting some parameters about the redistributed routes for example, the metric. The full syntax of the redistribute command is as follows redistribute protocol process-id level-1 level-1-2 level-2 as-number metric...
Class Based WFQ and Low Latency Queuing
Cisco created CBWFQ and LLQ using some of the best concepts from PQ, CQ, and WFQ, while adding several additional features. CBWFQ reserves bandwidth for each queue, and provides the ability to use WFQ concepts for packets in the default (class-default) queue. LLQ adds to CBWFQ the concept of a priority queue, but unlike PQ, LLQ prevents the high-priority queue from starving other queues. Additionally, both CBWFQ and LLQ use MQC for configuration, which means that they have robust classification...
Committed Access Rate
CAR implements single-rate, two-color policing. As compared with that same option in CB Policing, CAR and CB Policing have many similarities. They both can police traffic either entering or exiting an interface or subinterface they can both police subsets of that traffic based on classification logic and they both set the rate in bps, with Bc and Be configured as a number of bytes. CAR differs from CB Policing regarding four main features, as follows KEY CAR uses the rate-limit command, which...
BGP Communities
The BGP COMMUNITY PA provides a mechanism by which to group routes so that routing policies can be applied to all the routes with the same community. By marking a set of routes with the same COMMUNITY string, routers can look for the COMMUNITY string and then make policy decisions like setting some PA that impacts the BGP decision process, or simply filtering the routes. BGP communities are powerful in that they allow routers in one AS to communicate policy information to routers that are one...
Ldptdp Session Establishment
When you start MPLS on the first interface in a router, the TDP LDP process is started and the Label Information Base (LIB) structure is created. The router also tries to discover other LSRs on the interfaces running MPLS through TDP hello packets. The TDP hello packets are sent as broadcast or multicast UDP packets, making LSR neighbor discovery automatic. The debug tag tdp transport command can monitor the TDP hellos. Example C-4 shows the TDP process startup and Example C-5 illustrates the...
Building BGP Neighbor Relationships
BGP neighbors form a TCP connection with each neighbor, sending BGP messages over the connections culminating in BGP Update messages that contain the routing information. Each router explicitly configures its neighbors' IP addresses, using these definitions to tell a router with which IP addresses to attempt a TCP connection. Also, if a router receives a TCP connection request (to BGP port 179) from a source IP address that is not configured as a BGP neighbor, the router rejects the request....
The BGP Decision Process
The BGP decision process uses some of the PAs listed in Table 13-7, as well as several others. This section focuses on the decision process as an end to itself, with only brief explanations of new features or PAs. Following that, the text explains the details of some of the PAs that have not yet been covered in the book, as well as some other details that affect the BGP decision process. When a BGP router learns multiple routes to the same NLRI, it must choose a single best route to reach that...
Ethernet Address Formats
The IEEE intends for unicast addresses to be unique in the universe by administering the assignment of MAC addresses. The IEEE assigns each vendor a code to use as the first 3 bytes of its MAC addresses that first half of the addresses is called the Organizationally Unique Identifier (OUI). The IEEE expects each manufacturer to use its OUI for the first 3 bytes of the MAC assigned to any Ethernet product created by that vendor. The vendor then assigns a unique value in the low-order 3 bytes for...
Well Known Multicast Addresses
IANA controls the assignment of IP multicast addresses. To preserve multicast addresses, IANA is reluctant to assign individual IP multicast addresses to new applications without a good technical justification. However, IANA has assigned individual IP multicast addresses to popular network protocols. IANA has assigned several ranges of multicast IP addresses for specific types of reasons. Those types are as follows KEY Permanent multicast groups, in the range 224.0.0.0-224.0.1.255 POINT...
Switch Security Best Practices for Unused and User Ports
The first three items in the list of best practices for unused and user ports are mostly covered in earlier chapters. For a brief review, Example 21-7 shows an example configuration on a Cisco 3550 switch, with each of these items configured and noted. In this example, fa0 1 is a currently unused port. CDP has been disabled on the interface, but it remains enabled globally, on the presumption that some ports still need CDP enabled. DTP has been disabled as well, and STP Root Guard and BPDU...
Checks Before Becoming BGP Neighbors
Similar to IGPs, BGP checks certain requirements before another router may become a neighbor, reaching the BGP established state. Most of the settings are straightforward the only tricky part relates to the use of IP addresses. The following list describes the checks that BGP performs when forming neighbor relationships KEY 1. The router must receive a TCP connection request with a source address that the router finds pOINT in a BGP neighbor command. 2. A router's ASN (on the router bgp asn...
Label Imposition at the Network Edge
Label imposition has been described already as the act of prepending a label to a packet as it enters the MPLS domain. This is an edge function, which means that packets are labeled before they are forwarded to the MPLS domain. To perform this function, an Edge-LSR needs to understand where the packet is headed and which label, or stack of labels, it should assign to the packet. In conventional Layer 3 IP forwarding, each hop in the network performs a lookup in the IP forwarding table for the...
NonIP Header Marking Fields
As IP packets pass through an internetwork, the packet is encapsulated in a variety of other headers. In several cases, these other headers have QoS fields that can be used for classification and marking. Ethernet supports a 3-bit QoS marking field, but the field only exists when the Ethernet header includes either an 802.1Q or ISL trunking header. IEEE 802.1Q defines its QoS field as the 3 most-significant bits of the 2-byte Tag Control field, calling the field the user-priority bits. ISL...
T1 Framing and Encoding
The CSU DSUs on each end of a T1 link apply framing logic to the serial data stream in each direction on the link. The framing process allows a device to identify the individual DS0 channels, as well as overhead bits. The overhead bits are used for synchronization and framing, management, and a CRC error check. T1s use either the older Superframe (SF, also known as D4) framing standard or the Extended Superframe (ESF) frame format. E1 lines use either the ITU G.704 or G.706 standard. Using a T1...
Filtering BGP Updates Based on NLRI
Most of the logic behind BGP distribution lists, prefix lists, and route maps has already been covered in previous chapters. For example, Chapter 11 explains the logic behind the ip prefix-list command, and Chapters 8 through 10 cover filtering in IGP routing protocols using the distribute-list command. This section shows some brief examples to cover the syntax when these methods are used with BGP, plus a few quirks unique to BGP. One difference between BGP distribute lists and IGP distribute...
BGP Messages and Neighbor States
The desired state for BGP neighbors is the established state. In that state, the routers have formed a TCP connection, and they have exchanged Open messages, with the parameter checks having passed. At this point, topology information can be exchanged using Update messages. Table 12-3 lists the BGP neighbor states, along with some of their characteristics. Note that if the IP addresses mismatch, the neighbors settle into an active state. BGP uses four basic messages. Table 12-4 lists the...
Becoming Neighbors Exchanging Databases and Becoming Adjacent
OSPF directly encapsulates the five different types of OSPF messages inside IP packets, using IP protocol 89, as listed in Table 10-2. Used to discover neighbors, bring a neighbor relationship to a 2-way state, and monitor a neighbor's responsiveness in case it fails Used to exchange brief versions of each LSA, typically on initial topology exchange, so that a router knows a list of that neighbor's LSAs A packet that identifies one or more LSAs about which the sending router would like the...
Redistributing a Subset of Routes Using a Route
Route maps can be referenced by any redistribute command. The route map may actually let all the routes through, setting different route attributes (for example, metrics) for different routes. Or, it may match some routes with a deny clause, which prevents the route from being redistributed. (Refer to Figure 11-1 for a review of route map logic.) Figure 11-3 and Example 11-2 show an example of mutual redistribution between EIGRP and OSPF, with some routes being either filtered or changed using...
User Mode and Privileged Mode AAA Authentication
The term authentication, authorization, and accounting (AAA) refers to a variety of common security features. This section focuses on the first A in AAA authentication and how it is used to manage access to a router or IOS switch's user mode and privileged mode. The strongest authentication method to protect the CLI is to use a TACACS+ or RADIUS server. The Cisco Secure Access Control Server (ACS) is a Cisco Systems software product that can be installed on Unix, Linux, and several Windows...
Comparison of IGMPvl IGMPv2 and IGMPv3
Table 19-5 compares the important features of IGMPvl, IGMPv2, and IGMPv3. Table 19-5 Comparison of IGMPvl, IGMPv2, andIGMPv3 Table 19-5 Comparison of IGMPvl, IGMPv2, andIGMPv3 First Octet Value for the Query Message Destination Address for the General Query Joining multicast group address and source address Is Report Suppression Mechanism Available Can Maximum Response Time Be Configured Can a Host Send a Leave Group Message Destination Address for the Leave Group Message Table 19-5 Comparison...
Frame Relay Traffic Shaping Configuration
Frame Relay Traffic Shaping (FRTS) differs from CB Shaping in several significant ways, although the underlying token-bucket mechanics are identical. The following list highlights some of the key similarities and differences KEY FRTS can be used only on Frame Relay interfaces, whereas CB Shaping can be used with any po NT underlying data link protocol. Like CB Shaping, FRTS allows a large number of IOS queuing tools to be used instead of a single FIFO shaping queue. Unlike CB Shaping, FRTS does...
Network Address Translation
NAT, defined in RFC 1631, allows a host that does not have a valid registered IP address to communicate with other hosts on the Internet. NAT has gained such wide-spread acceptance that the majority of enterprise IP networks today use private IP addresses for most hosts on the network and use a small block of public IP addresses, with NAT translating between the two. NAT translates, or changes, one or both IP addresses inside a packet as it passes through a router. (Many firewalls also perform...
IP Addressing and Subnetting Review
First, here's a quick review of some of the core facts about IPv4 addresses that should be fairly familiar to you Written in dotted decimal notation (for example, 1.2.3.4), with each decimal octet representing 8 bits. Addresses are assigned to network interfaces, so computers or routers with multiple interfaces have multiple IP addresses. A computer with an IP address assigned to an interface is an IP host. A group of IP hosts that are not separated from each other by an IP router are in the...
Hsrp Vrrp and GLBP
IP hosts can use several methods of deciding which default router or default gateway to use DHCP, BOOTP, ICMP Router Discovery Protocol (IRDP), manual configuration, or even by running a routing protocol (although having hosts run a routing protocol is not common today). The most typical methods using DHCP or manual configuration result in the host knowing a single IP address of its default gateway. Hot Standby Router Protocol (HSRP), Virtual Router Redundancy Protocol (VRRP), and Gateway Load...
MPLS Label Stack Header
For various reasons, switching performance being one, the MPLS label must be inserted in front of the labeled data in a frame-mode implementation of the MPLS architecture. The MPLS label thus is inserted between the Layer 2 header and the Layer 3 contents of the Layer 2 frame, as displayed in Figure C-11. Figure C-11 Position of the MPLS Label in a Layer 2 Frame Unlabeled IP packet in Layer 2 frame Unlabeled IP packet in Layer 2 frame Due to the way an MPLS label is inserted between the Layer 3...
The CCIE Routing and Switching Written Exam 350001
The CCIE Routing and Switching written exam, at least as of the time of publication, consists of a 2-hour exam administered at a proctored exam facility affiliated either with Pearson VUE (http www.VUE.com cisco) or Thomson Prometric (http www.2test.com). The exam typically includes approximately 100 multiple-choice questions, with no simulation questions currently on the written exam. Because the written exam is typically followed at some point by an attempt at passing the lab exam, Cisco has...
Filtering Subnets of a Summary Using the aggregateaddress Command
Manual BGP route summarization, using the aggregate-address BGP router subcommand, provides the flexibility to allow none, all, or a subset of the summary's component subnets to be advertised out of the BGP table. By allowing some and not others, the aggregate-address command can in effect filter some routes. The filtering options on the aggregate-address command are as follows KEY Filtering all component subnets of the summary from being advertised, by using the POINT summary-only keyword...
Dynamically Finding RPs and Using Redundant RPs
In a PIM-SM network, every router must somehow learn the IP address of an RP. A PIM-SM router can use one of the following three methods to learn the IP address of an RP KEY The RP address can be statically configured on all the PIM-SM routers with the Cisco IOS POINT global command ip pim rp-address address. This is the method used for the five-router topology shown in Figure 20-19. The Cisco-proprietary Auto-RP protocol can be used to designate the RP and advertise its IP address so that all...
VTP Process and Revision Numbers
The VTP update process begins when a switch administrator, from a VTP server switch, adds, deletes, or updates the configuration for a VLAN. When the new configuration occurs, the VTP server increments the old VTP revision number by 1, and advertises the entire VLAN configuration database along with the new revision number. The VTP revision number concept allows switches to know when VLAN database changes have occurred. Upon receiving a VTP update, if the revision number in a received VTP...
Step 4 Shortest ASPATH
Routers can easily determine the shortest AS_PATH length by using a few rules that define how to account for all four parts of the AS_PATH the AS_SEQ, AS_SET, AS_CONFED_SEQ, and AS_CONFED_SET. Additionally, routing policies can change the number of ASNs in the AS_PATH. Table 13-12 summarizes the key points regarding AS_PATH length. Table 13-12 Features that Impact the Total Number of ASs in the AS PATH Length Calculation Table 13-12 Features that Impact the Total Number of ASs in the AS PATH...
Why Should I Take the CCIE Routing and Switching Written Exam
The first and most obvious reason to take the CCIE Routing and Switching written exam is that it is the first step toward obtaining the CCIE Routing and Switching certification. Also, you cannot schedule a CCIE lab exam until you pass the appropriate written exam. In short, if you want all the professional benefits of a CCIE Routing and Switching certification, you start by passing the written exam. The benefits of getting a CCIE certification are varied, but here are just a few of the reasons...
PPP Compression
PPP can negotiate to use Layer 2 payload compression, TCP header compression, and or RTP header compression. Each type of compression has pros and cons, with the most obvious relating to what is compressed, as shown in Figure 17-4. Figure 17-4 Fields Compressed with Compression Features TCP Header Compression RTP Header Compression TCP Header Compression RTP Header Compression Comparing payload compression and header compression, payload compression works best with longer packet lengths, and...
RIP Next Hop Feature and Split Horizon
This section covers the split horizon and next-hop features of RIPv2. These two features do not typically need to be considered at the same time, but in some cases they do. The example used in this section shows how the two features may be needed in the same design. First, Cisco IOS controls the split horizon setting per interface, using the no ip split-horizon interface subcommand. Split horizon is on by default, except for cases in which Frame Relay is configured with the IP address on the...
CB Policing Concepts
CB Policing is enabled for packets either entering or exiting an interface, or those entering or exiting a subinterface. It monitors, or meters, the bit rate of the combined packets when a packet pushes the metered rate past the configured policing rate, the policer takes action against that packet. The most aggressive action is to discard the packet. Alternately, the policer can simply re-mark a field in the packet. This second option allows the packets through, but if congestion occurs at...
About the Technical Reviewers
Maurilio Gorito, CCIE No. 3807, works for Cisco Systems, Inc., as part of the CCIE team. As content manager, Maurilio is responsible for managing the content development process for the CCIE Routing and Switching lab and written exams and proctoring the CCIE Routing and Switching, Service Provider, and CCIE Security lab exams. Rus Healy, CCIE No. 15025, is program manager for Technical Training and Certifications for Microwave Data Systems in Rochester, New York, a leading manufacturer of data...
IGMPvl and IGMPv2 Interoperability
IGMPv2 is designed to be backward compatible with IGMPvl. RFC 2236 defines some special interoperability rules. The next few sections explore the following interoperability scenarios IGMPv2 Host and IGMPv1 Routers Defines how an IGMPv2 host should behave in the presence of an IGMPvl router on the same subnet. IGMPv1 Host and IGMPv2 Routers Defines how an IGMPv2 router should behave in the presence of an IGMPvl host on the same subnet. IGMPv1 and IGMPv2 Routers Defines how an IGMPv2 router...
Operation of Protocol Independent Multicast Sparse Mode
PIM-SM works with a completely opposite strategy from that of PIM-DM, although the mechanics of the protocol are not exactly opposite. PIM-SM assumes that no hosts want to receive multicast packets until they specifically ask to receive them. As a result, until a host in a subnet asks to receive multicasts for a particular group, multicasts are never delivered to that subnet. With PIM-SM, downstream routers must request to receive multicasts using PIM Join messages. Also, once they are...
Frame Relay Configuration Basics
Two of the most important details regarding Frame Relay configuration are the association of DLCIs with the correct interface or subinterface, and the mapping of L3 addresses to those DLCIs. Interesting, both features can be configured using the same two commands the frame-relay map and frame-relay interface-dlci commands. Chapter 7 already covered the details of mapping L3 addresses to DLCIs using InARP and static mapping. (If you have not reviewed those Table 18-3 Frame Relay FECN, BECN, and...
Generic Terms and Characteristics of BGP PAs
Each BGP PA can be described as either a well-known or optional PA. These terms refer to whether a particular implementation of BGP software must support the PA (well known) or support for the PA is not required (optional). Well-known PAs are either one of the following Mandatory The PA must be in every BGP Update Discretionary The PA is not required in every BGP Update These classifications relate not to the capabilities of a BGP implementation, but rather to whether a particular feature has...
Port Fast Uplink Fast and Backbone Fast
The Cisco-proprietary PortFast, UplinkFast, and BackboneFast features each solve specific STP problems. Table 3-5 summarizes when each is most useful, and the short version of how they improve convergence time. Table 3-5 PortFast, UplinkFast, and BackboneFast Used on access ports that are not connected to other switches or hubs Immediately puts the port into forwarding state once the port is physically working Used on access layer switches that have multiple uplinks to distribution core...
Subnetting Math
Knowing how to interpret the meaning of addresses and masks, routes and masks in the routing table, addresses and masks in ACLs, and configure route-filtering are all very important topics for the CCIE Routing and Switching written and lab exams. This section covers the binary math briefly, with coverage of some tricks to do the math quickly without binary math. Several subsequent chapters cover the configuration details of features that require this math. Dissecting the Component Parts of an...
Tuning Shaping for Voice Using LLQ and a Small Tc
Example 16-1 in the previous section shows default settings for queuing for the interface software queues (WFQ) and for the shaping queue (FIFO). Example 16-2 shows an alternative configuration that works better for voice traffic by using LLQ for the shaped traffic. Also, the configuration forces the Tc down to 10 ms, which means that each packet will experience only a short delay waiting for the beginning of the next Tc. By keeping Tc to a small value, the LLQ logic applied to the shaped...
Filtering BGP Updates by Matching the Aspath Pa
To filter routes by matching the AS_PATH PA, Cisco IOS uses AS_PATH filters. The overall configuration structure is very similar to BGP distribute lists and prefix lists, with the matching logic specified in a list, and the logic being applied with a neighbor command. The main two steps are as follows 1. Configure the AS_PATH filter using the ip as-path access-list number permit deny regex command. 2. Enable the AS_PATH filter using the neighbor neighbor-id filter-list as-path-filter-number in...
