Routing and Switching Written Qualification Exam (350-001) Table of Contents Cisco Device Operation Commands Infrastructure Configuration Register Configuration Register Software Configuration Bit Meanings Bunch of Bits (some of the more interesting Configuration Register Bits, and what they do) More Bits 10 Seeing and Changing Configuration Register Settings 11 Boot Command 11 My simplistic description of the boot sequence 11 Operations 11 Password recovery 11 Copying and Backing up Configuration Files 11 Configuring a new router 12 Security & Passwords 12 General Networking Theory 13 OSI Models 13 MAC Addressing 13 General Routing Concepts 14 Standards 15 Ethernet Cable Specifications 15 Protocol Mechanics 16 Transmission Control Protocol (TCP) 16 Fragmentation & MTU 17 Bridging and LAN Switching 17 Transparent Bridging (TB) 17 Translational Bridging 18 Integrated Routing and Bridging (IRB) 18 Bridge ACL & Filtering 18 Multiple-Instance Spanning Tree Protocol (MISTP) 19 Source-Route Bridging (SRB) 19 Data Link Switching (DLSw) and DLSw+ 20 Source-Route Transparent Bridging (SRT) and Source-Route Translational Bridging (SR/TLB) 20 LAN Switching 21 Routing and Switching Written Qualification Exam (350-001) Switching Technique Types 21 Command-Line Interface (CLI) 21 Trunking 22 Virtual LAN (VLAN) 23 VLAN Trunk Protocol (VTP) 23 Spanning-Tree Protocol (STP) 23 Root Bridges and Switches 24 Bridge Protocol Data Units (BPDUs) 24 How STP Works 24 STP Timers 24 Ports in an STP domain will progress through the following states: 24 Notes about STP Port States: 25 STP Enhancements: 25 DISL 26 Fast Ether Channel (FEC) 26 Cisco Discovery Protocol (CDP) 26 CGMP 26 Security 26 802.1X 27 Multi-Layer Switching (MLS) 27 Multi-Layer Switching (MLS) 28 Internet Protocol (IP) 28 IP Addressing 28 Subnetting 28 Subnetting Tricks 29 Route Summarization 29 Services & Applications 30 DNS 30 ARP & RARP 30 BOOTP & DHCP 30 ICMP 31 NAT 31 HSRP & VRRP 31 Telnet 32 FTP & TFTP 32 SNMP 32 Access Control Lists (ACL) 32 Routing and Switching Written Qualification Exam (350-001) Access list types are designated by the list Numbers: 33 Internet Protocol Version (IPv6) 33 IP Routing 34 Routing Protocol Concepts 34 Distance-Vector Routing Protocols 34 Link State Routing Protocols 34 Hybrid Routing Protocols 34 Distribution Lists 35 Routing Loops 35 Administrative Distance 36 Open Shortest Path First (OSPF) 36 Area 37 OSPF Area Types: 37 Stub and Totally Stubby Area Similarities: 37 Stub and Totally Stubby Area Differences: 38 Router Types: 38 Traffic Types: 38 NMBA Networks 38 LSA Types: 39 Routing Authentication 39 Border Gateway Protocol (BGP) 39 Synchronization/Full Mesh 40 Next-Hop-Self Command 40 BGP Path Selection 40 Scalability Problems (and Solutions) with IBGP 41 Configuring Neighbors & Networks 41 Route Dampening 41 Enhanced Interior Gateway Routing Protocol (EIGRP) 42 Tables: 42 Choosing routes: 43 Intermediate System-to-Intermediate System (IS-IS) 43 Access-Control & Filtering 44 Distribution Lists 44 Route-Maps 44 Policy Routing 45 Redistribution 45 Route-Tagging 45 Routing and Switching Written Qualification Exam (350-001) Dial-on-Demand Routing (DDR) 45 DDR has two important applications: 45 Encapsulation Methods for DDR: 45 Dial Backup 45 Interior Gateway Routing Protocol (IGRP) 46 Router Information Protocol (RIP) Version and 46 QoS 46 Fancy Queuing 46 Weighted Fair Queuing (WFQ) 46 Priority Queuing 47 Custom Queuing 47 Packet over SONET/SDH (PoS) and IP Precedence 47 Class of Service (CoS) 47 Random Early Detection (RED) and Weighted RED (WRED) 48 Weighted Round-Robin (WRR)/Queue Scheduling 48 Weighted Round-Robin (WRR)/Queue Scheduling 49 Shaping vs Policing / Committed Access Rate (CAR) 49 Committed Access Rate (CAR) 49 Network-Based Application Recognition (NBAR) 50 Configuring NBAR 50 802.1x 51 Differentiated Services Code Point (DSCP) 51 WAN 51 Integrated Services Digital Network (ISDN) 51 ISDN Specifics 52 Channels 53 Flavors of ISDN 53 Point-to-Point Protocol (PPP) 53 OSPF and ISDN 53 Frame Relay 53 Types of Circuits 54 Data Link Connection Identifier (DLCI) 54 Local Management Interface (LMI) 54 Encapsulation 54 Frame-Relay Traffic Shaping (FRTS) 54 Frame-Relay Compression 55 Frame-Relay Mapping 55 Routing and Switching Written Qualification Exam (350-001) Split Horizon and Frame Relay Interfaces 55 Speed Elements 55 Asynchronous Transfer Mode (ATM) 55 ATM is comprised of four major layers: 56 ATM Adaptation Layer (AAL) 56 IISP and PNNI 56 NSAP Format ATM Addresses 57 Service-Specific Connection-Oriented Protocol (SSCOP) 57 RFC 1483 & RFC 2684 – Multiprotocol Encapsulation over AAL5 57 ATM Mapping 57 Physical Layer 58 Serial Interface Abbreviations 58 Is Your Interface a DTE or a DCE? 58 RS-232 58 V.35 Interface 59 Troubleshooting Serial Links 59 Show Controllers Command 61 Serial Line Conditions 62 Debug Commands 62 Increasing Output Drops 63 Increasing Input Drops 63 Excessive Aborts 64 Clocking Problems 64 Increasing Interface Resets on a Serial Link 65 Increasing Carrier Transitions Count on Serial Link 65 CRC and Framing Errors 66 SONET / SDH 66 T1 Encoding 66 Leased Line Protocols 67 HDLC 67 PPP 67 Packet over SONET (PoS) 67 DPT / SRP 67 LAN 68 Ethernet/FE/GE 68 Ethernet/Fast Ethernet/Gigabit Ethernet 68 Fast EtherChannel (FEC) 68 Routing and Switching Written Qualification Exam (350-001) Carrier Sense Multiple Access Collision Detect (CSMA/CD) 68 Wireless/802.11 69 Deployment issues for wireless include: 69 Wireless Security 69 Important wireless networking terms: 70 Radio Frequency (RF) Terms: 70 Cisco Deployments 70 Multiservice 71 Voice/Video 71 Coder-decoders (Codecs) 71 Signaling System (SS7) 71 Signaling System (SS7) 72 Real-Time Transport Protocol (RTP) 72 Real-Time Transport Control Protocol (RTCP) 72 Session Initiation Protocol (SIP) 72 Multiprotocol Label Switching (MPLS) 72 Definitions follow for the MPLS terms: 73 MPLS Operations 73 How the LFIB is Propagated 74 Quality of Service and Traffic Engineering 74 IP Multicast 74 Addressing 75 Translate Multicast Addresses into Ethernet MAC addresses 76 Internet Group Management Protocol (IGMP) and Cisco Group Management Protocol (CGMP) 77 IGMP 77 CGMP 78 IGMP Snooping 78 Multicast Distribution Trees 79 Protocol Independent Multicast (PIM) 79 PIM-Spare Mode Mechanics 80 PIM-SM Joining & Pruning 80 IP Multicast Routing Table (mroute) 80 Distribution Trees 80 Rendezvous Points 80 Bootstrap Router (BSR) 81 Routing and Switching Written Qualification Exam (350-001) Cisco Device Operation Commands Cisco routers are configured and maintained primarily through the issuing of IOS commands If you have reached the point of preparing for the CCIE Written exam, I must assume that you have spent considerable time configuring Cisco routers and switches You should, however, make sure you have a complete understanding of how the different technologies are configured, and thorough knowledge of the show and debug commands that are used to troubleshoot them A note on debug commands: you should know that debug commands can seriously stress the resources of a router, and they should be used carefully and as conservatively as possible when working in a production environment Infrastructure The infrastructure of a Cisco router includes the main board, memory, CPU, Flash and interfaces You should understand what each of these devices does, and how they interact The most commonly misunderstood are: RAM (Random Access Memory) – In all but a few low-end routers like 2500’s, the RAM holds the running version of the IOS and the current running configuration This is also where the routing tables, caches, and queues are stored Remember that when the router is powered-off, everything in RAM is lost ROM (Read-Only Memory) – Holds some basic router commands and usually a limited version of Cisco IOS (Internetwork Operating System) It also houses the power-on diagnostics and the bootstrap program The ROM is read-only and cannot be changed NVRAM (Non-Volatile Random Access Memory) – This is where the router’s saved configuration file is stored This information will not be lost if the router is powered down Flash memory – Home for the router’s IOS image and microcode Prior to installing any IOS, ensure that you have enough flash to support the proposed image Depending on the version and feature set of the IOS, the image can be of various sizes Newer versions with more powerful features will often require additional flash Remember that files deleted from flash can remain in place, marked for deletion, until the “squeeze” command is issued Routing and Switching Written Qualification Exam (350-001) Configuration Register Early Cisco routers had a set of hardware switches that controlled certain aspects of the router’s performance, such as the boot sequence This was phased out some time ago, but there is now a software equivalent, the sixteen-bit Software Configuration Register, which is written into nonvolatile memory Common reasons for modifying the register include: Recovering a lost password Changing the router boot configuration to allow Flash or ROM boot Loading an image into Flash memory Enabling or disabling the console break key Here are some of the common Configuration Register values: 0x2102 – The most common value, which establishes booting to flash and NVRAM 0x2142 – The value used most commonly to recover passwords 0x2100 – Boots using the bootstrap found in ROM Software Configuration Bit Meanings * Please note that a boot system global command in the router’s NVRAM configuration will override the default net-boot filename Routing and Switching Written Qualification Exam (350-001) Bunch of Bits (some of the more interesting Configuration Register Bits, and what they do) Bits 0,1,2 and are known collectively as the boot field, and determine where the router will load its IOS image from If the boot field value is 0x0, you will need to boot the operating system manually by entering the “b” command at the bootstrap prompt If the boot field value is 0x1 (the factory default), the router will boot using the default ROM software If the boot field has any other value, the router uses the resulting number to form a default boot filename for network booting, which is created as part of the automatic configuration process To form the boot filename, the server starts with the word “cisco”, attaches the octal equivalent of the boot field number, then a dash, and finally the processor-type name The following table lists the default boot filenames for boot field values between 0x2 and 0xf on an IGS router Default Boot Filenames Bit Bit Bit Bit Hex Value Net-boot Filename 0 0x2 cisco2-igs 0 1 0x3 cisco3-igs 0 0x4 cisco4-igs 1 0x5 cisco5-igs 1 0x6 cisco6-igs 1 0x7 cisco7-igs 0 0x8 cisco10-igs 0 0x9 cisco11-igs 1 0xa cisco12-igs 1 0xb cisco13-igs 1 0 0xc cisco14-igs 1 0xd cisco15-igs 1 0xe cisco16-igs 1 1 0xf cisco17-igs It’s important to remember that the boot sequence, baring the involvement of “boot system” commands in the configuration, is Flash, Network, ROM Routing and Switching Written Qualification Exam (350-001) Leased Line Protocols HDLC High Level Data Link Control (HDLC) is one of the more common Data-Link (OSI Layer 2) protocols HDLC is the default encapsulation protocol on all Cisco serial interfaces HDLC is primarily used on leased lines (dedicated pointto-point lines) but it can also be used on dialup links The version of HDLC used on Cisco routers is proprietary PPP Point to Point Protocol (PPP) encapsulation protocol is commonly used on dial-up links but can also be used on point-to-point leased lines PPP replaced SLIP as the primary dialup protocol in use today PPP can assign IP addresses to the dialup clients, perform Multi-link PPP if you have multiple connections, monitor link quality, detect errors, and compress data going over the link PPP consists of three parts: Encapsulation - using HDLC frames Link Control Protocol (LCP) – used to connect, monitor, and disconnect circuits Network Control Programs (NCP) – used to support multiple upper-layer protocols To authenticate the remote system, PPP supports a variety of authentication protocols They are: Password Authentication Protocol (PAP) – sends username & password in clear-text Challenge Handshake Authentication Protocol (CHAP) – encrypts passwords Microsoft CHAP (MS-CHAP) – Microsoft’s version of CHAP Packet over SONET (PoS) Cisco PoS has the IP layer riding directly above the SONET layer, eliminating the overhead usually required to run IP over ATM and SONET, while still offering strong quality-of-service (QoS) guarantees PoS was designed to overcome some of the limitations of IP that restricted its direct use on very high-speed links, and addressing some of the QoS issues inherent with IP DPT / SRP Dynamic Packet Transport (DPT) is a Cisco optical protocol It uses dual, counter-rotating rings to send & receive data Spatial Reuse Protocol (SRP) is a MAC-layer protocol that is used with DPT SRP uses destination-stripping for the most efficient use of bandwidth possible SRP also provides a high level of redundancy called Intelligent Protection Switching (IPS) DPT/SRP uses fairness algorithms to ensure all stations connected to the ring get equal time/bandwidth DPT/SRP rings can work on underlying technologies like SONET and WDM (wave-division multiplexing) Routing and Switching Written Qualification Exam (350-001) LAN Ethernet/FE/GE There are two types of Ethernet, which are very similar but with a few significant differences: 802.3 – Has a two-byte length field (instead of a protocol type field) The protocol information is held in two fields: DSAP (Destination Service Access Protocol) and SSAP (Source Service Access Protocol) 802.3 runs at 10Mbs, 100Mbs, or 1,000Mbs and supports all of layer one, and part of layer two of the OSI model Ethernet II - Has a two-byte protocol type field that indicates the protocol of the data that is being sent (instead of a length field) Ethernet II runs at 10Mbs and supports layers one and two of the OSI model Ethernet/Fast Ethernet/Gigabit Ethernet Legacy Ethernet runs at 10Mbps, and can still be found at the Access layer of some older installations that have a significant investment in legacy technology, or where the communications requirements are very low Most print servers, such as Intel NetPorts and HP JetDirects, are 10Mbps devices Fast Ethernet (100Mbps) has largely replaced legacy Ethernet at all three layers of the hierarchical model (Core, Distribution, Access layers) to become the most common LAN technology Most Fast Ethernet equipment is capable of using out-of-bank Fast Link Pulse (FLP) bursts to auto-negotiate the fastest physical layer technology that can be used by both communicating devices This provides a parallel detection function for half- and full-duplex 1BaseT, half- and full-duplex 100BaseTX, and 100BaseT4 physical layers Gig Ethernet is more expensive and will normally be found either at the Core or Distribution layers, although as perport costs come down and the technology becomes cheaper, you can expect to see it more commonly at the access layer Uplinks between phone closets and the computer room will often be Gigabit links over fiber; the higher speed allowing the consolidation of access device data streams, and the fiber overcoming distance limitations The most significant limitation of Ethernet is collisions These become more prevalent as utilization increases This can reach levels where higher-layer applications are affected, or time sensitive protocols time-out The most common problems with Ethernet installations include reconciling configuration elements, like speed, duplex and encapsulation settings Fast EtherChannel (FEC) FEC is a Cisco proprietary method for aggregating the bandwidth of up to four Fast Ethernet channels (or two Gigabit Ethernet channels) on a switch and having them appear to be one logical connection The requirements are that all the ports be in the same VLAN; have the same speed and duplex settings; and, if the switch is not a Cat6000, that contiguous ports be used Besides increasing the bandwidth available between devices, this also adds a level of protection, because if one of the links within the EtherChannel were to go down, the traffic would continue to pass at the reduced rate without interruption The Port Aggregation Protocol (PAgP) allows automatic creation of EtherChannels by exchanging packets between eligible Ethernet ports (those in auto and desirable modes; ports in on or off mode not exchange PAgP packets) The protocol learns the capabilities of port groups dynamically, and then groups the ports into an EtherChannel Carrier Sense Multiple Access Collision Detect (CSMA/CD) Defined by the IEEE 802.3, CSMA/CD listens on the Ethernet segment before transmitting; if a collision occurs, the station that detects it sends out a jam signal to alert all other machines to stop trying to send After the signal stops, the machines wait for a random period of time before attempting transmission again Routing and Switching Written Qualification Exam (350-001) Wireless/802.11 Although the first wireless networks appeared over two decades ago, adoption has been slow because: The original wireless data rates were inadequate (way too slow) Proprietary solutions dominated the marketplace, providing little interoperability among devices Wireless solutions were very expensive In 1999, the IEEE ratified the 802.11b standard with data rates up to 11 Mbps, and interest in Wireless LANs (WLANs) exploded Vendor interoperability is ensured by the Wireless Ethernet Compatibility Alliance (WECA), an independent international nonprofit association that identifies compliant products from more than 140 companies spanning component manufacturers, equipment vendors, and service providers under its "Wi-Fi" Brand As with any new technology, wireless is continually evolving Multiple standards that offer advancements in speed, bandwidth and security either exist, or are being developed to compete for dominance in the high-bandwidth WLAN market These include: 802.11b – This is the most widely deployed wireless standard, and can be found in both corporate and home wireless markets, with wireless "hot spots" popping up in hotels, airports, convention centers, and coffee shops worldwide It operates in the 2.4 GHz unlicensed radio band and delivers a maximum data rate of 11 Mbps 802.11a Operates in the unlicensed portion of the GHz radio band, making 802.11a immune to interference from devices that operate in the 2.4 GHz band, such as microwave ovens, cordless phones, and Bluetooth (a short-range, low-speed, point-to-point, personal-area-network wireless standard) 802.11a has a top data rate of 54 Mbps, nearly five times the bandwidth of 802.11b It is the first of the higher-speed wireless standards to hit the market, but has a major drawback in that it does not provide interoperability with existing 802.11b equipment 802.11g A late entry, this standard boasts a top data rate of 54 Mbps, but operates in the same unlicensed portion of the 2.4-GHz spectrum as 802.11b, making it backward compatible with 802.11b devices This new standard is limited to the same three channels and crowded 2.4-GHz band as 802.11b, creating possible scalability and interference issues Deployment issues for wireless include: Interference sources: If an environment has a lot of interference sources in the 2.4-GHz frequency band, such as Bluetooth devices or non-802.11b wireless phones, then 802.11a (5 GHz) may be the better choice Need for channels: 802.11b offers only three nonoverlapping frequency channels; 802.11a offers eight for more flexibility in structuring coverage areas Installed base: The more 802.11b clients that are installed, the greater the need to have access points that support 802.11b Types of applications: 802.11b is better for transaction-intensive applications; 802.11a is better for data-hungry applications Cost: 802.11a systems could cost 20 to 30 percent more than current 802.11b products and may have a higher deployment cost because of the different RF characteristics of the 5-GHz frequency Wireless Security Acknowledging the inherent security deficiencies of WLANs, the 802.11 committee adopted an encryption protocol, the Wired Equivalent Privacy (WEP) WEP does not provide authentication, access control, or data integrity checking; just encryption Routing and Switching Written Qualification Exam (350-001) Important wireless networking terms: Access Point (AP) - A wireless LAN transceiver that acts as a center point of an all-wireless network or as a connection point between wireless and wired networks Antenna - A device for transmitting or receiving a radio frequency (RF) Antennas are designed for specific and relatively tightly defined frequencies, and are quite varied in design An antenna designed for 2.4-GHz 802.11b devices will not work with 2.5-GHz devices Beamwidth - The angle of signal coverage provided by an antenna Beamwidth typically decreases as antenna gain increases Broadband - In general, a RF system is deemed "broadband" if it has a constant data rate at or in excess of 1.5 Mbps Its corresponding opposite is "narrowband." Fresnel Effect - A phenomenon related to line of sight whereby an object that does not obstruct the visual line of sight obstructs the line of transmission for radio frequencies Microcell - A bounded physical space in which numerous wireless devices can communicate Because it is possible to have overlapping cells as well as isolated cells, the boundaries of the cell are established by some rule or convention Multipath - The echoes created as a radio signal bounces off of physical objects Roaming - Movement of a wireless node between two microcells Roaming usually occurs in infrastructure networks built around multiple access points Spread Spectrum - A radio transmission technology that "spreads" the user information over a much wider bandwidth than otherwise required in order to gain benefits such as improved interference tolerance and unlicensed operation Wireless Access Protocol - A language used for writing Web pages that uses far less overhead, making it more preferable for wireless access to the Internet by personal digital assistants (PDAs) and Web-enabled cellular phones Radio Frequency (RF) Terms: Hz - The international unit for measuring frequency is hertz (Hz), which is equivalent to the older unit of cycles per second MHz - one million hertz GHz - one billion hertz Just to understand how these relate, standard U.S electrical power frequency is 60 Hz, the AM broadcast radio frequency band is 0.55-1.6 MHz, the FM broadcast radio frequency band is 88-108 MHz, microwave ovens typically operate at 2.45 GHz and wireless home phones typically run at 900MHz or 2.4 GHz Cisco Deployments Currently the most flexible Cisco wireless access point is the Aironet 1200 Series which provides compatibility for all the currently established and emerging wireless LAN standards It has a dual-band design with eight GHz channels, and three 2.4 GHz channels, enabling a mix of client devices Software and hardware are field upgradeable Routing and Switching Written Qualification Exam (350-001) Multiservice Voice/Video Voice and Video can be digitized and passed though a normal IP network as long as sufficient bandwidth is available, and the appropriate QoS issues are addressed These technologies require more coverage than can be provided in a short exam study guide; but for the purposes of this exam, and because you will probably face them in your career, you should develop an appreciation of Cisco’s Architecture for Voice, Video and Integrated Data (AVVID) AVVID technologies enable advanced voice and data services to be delivered reliably over a Cisco router and switch network An excellent place to begin this research is at: http://www.cisco.com/en/US/netsol/ns340/ns19/ns24/networking_solutions_packages_list.html Coder-decoders (Codecs) Codecs use pulse code modulation to turn analog signals into digital bit streams, and conversely, transform digital bit streams back into analog signals This function is required by Voice-over-IP (VoIP) gateways to turn human speech into digital data for transport, and back to analog sound to present it to the destination Common codecs specifications include: G.711 – The format used for digital voice delivery in the telecom world, this standard describes the 64 Kbps PCM voice encoding technique G.726 – Describes ADPCM coding at 40, 32, 24 and 16 Kbps and can be used to communicate between packet voice and other systems, provided the PBX or public phone system has ADPCM capability defined G.729 – Describes CELP compressions that allow voice to be encoded in Kbps streams This standard is further defined in two variations (G.729/G.729a) These provide standard voice-encoding algorithms that turn the actual audio signal to digital data These particular algorithms are significant in the VoIP arena because of the low-bandwidth requirement (8 Kbps), while providing speech quality comparable to a 32 Kbps ADPCM link G.731.1 – Describes a compression technique used to compress speech or the audio portion of a multimedia presentation, and is part of the H.324 family of standards There are two bit rates associated with this coder 5.3 and 6.3 The higher bit rate is based on MP-MLQ and provides a higher quality, while the lower rate is based on CELP and provides good quality Routing and Switching Written Qualification Exam (350-001) Signaling System (SS7) The international standard telephony network common channel signaling protocol that allows communication between the Public Switch Telephone Network (PSTN) and local phone switches It defines the protocols and procedures that allow the PSTN to exchange information for call setup, routing, and control Examples of telecom signaling would include many sounds we’re all familiar with, such as off-hook notification, dial tone, ringing, number dialing, busy signals and congestion (fast-busy) It also provides for out-of-band signaling and is responsible for routing, link status, and connection control Local phone number portability, 1-800 calling, in-network phone mail and portable phone roaming all are defined by SS7 These standards are used by both wireline (landline) and wireless telephony devices Because SS7 uses Common Channel Signaling (CCS) signaling, it allows Telecommunication providers to offer valueadded services, such as call waiting and caller ID Real-Time Transport Protocol (RTP) Provides support for applications with real-time requirements, such as Video- or Voice-over-IP networks This sessionlayer protocol uses UDP as its primary transport-layer protocol to minimize delay, and because retransmissions are not just unnecessary, but undesirable This is easy to see if, with VoIP, a small amount of lost traffic would be unnoticeable; traffic played-back out of order would be very difficult to understand RTP enhances the operation of connectionless UDP by providing sequence numbering, time-stamping and a payloadtype field that identifies the application or process that the data is being transported for Real-Time Transport Control Protocol (RTCP) Built on top of RTP, RTCP adds additional functionality for identification of the RTP source, limiting control traffic, secondary transports for small amounts of information, and statistics about the RTP stream Session Initiation Protocol (SIP) SIP is the IETF's standard ASCII-based, application-layer control protocol for multimedia conferencing over IP It establishes, maintains, and terminates calls between, and is designed to provide signaling and session management for, a packet telephony network Multiprotocol Label Switching (MPLS) In a normal routed environment, frames pass in a hop-by-hop manner based on layer-3 addressing in the header to determine the path to the destination Routing protocols have very little interest in the layer-2 characteristics of the network, particularly in regard to quality of service (QoS), traffic-management and loading Multiprotocol Label Switching (MPLS) fuses the intelligence of routing with the performance of switching, and provides significant benefits to networks with a pure IP architecture, as well as those with IP and ATM or a mix of other Layer technologies MPLS enables devices to specify paths through the network based upon QoS and bandwidth requirements of the applications, taking into account layer-2 attributes The non-proprietary MPLS protocol developed by IETF is loosely based on Cisco's proprietary tag-switching protocol Although the two protocols have much in common, they are different enough to prevent tag-switching devices from interacting directly with MPLS devices MPLS will likely supercede tag switching MPLS technology is key to scalable virtual private networks (VPNs) and end-to-end quality of service (QoS), enabling efficient utilization of existing networks to meet future growth and rapid fault correction of link and node failure The technology also helps deliver highly scalable, differentiated end-to-end IP services with simpler configuration, Routing and Switching Written Qualification Exam (350-001) management, and provisioning for both Internet providers and subscribers Definitions follow for the MPLS terms: Label—A header created by an edge label switch router (edge LSR) and used by label switch routers (LSR) to forward packets The header format varies based upon the network media type For example, in an ATM network, the label is placed in the VPI/VCI fields of each ATM cell header In a LAN environment, the header is a "shim" located between the Layer and Layer headers Label forwarding information base—A table created by a label switch-capable device (LSR) that indicates where and how to forward frames with specific label values Label switch router (LSR)—A device such as a switch or a router that forwards labeled entities based upon the label value Edge label switch router (edge LSR)—The device that initially adds or ultimately removes the label from the packet Label switched— An LSR making a forwarding decision based upon the presence of a label in the frame/cell Label-switched path (LSP)—The path defined by the labels through LSRs between end points Label virtual circuit (LVC)—An LSP through an ATM system Label switch controller (LSC)—An LSR that communicates with an ATM switch to provide and provision label information within the switch Label distribution protocol (LDP)—A set of messages defined to distribute label information among LSRs XmplsATM—The virtual interface between an ATM switch and an LSC MPLS Operations Frames enter the MPLS domain through an Edge label switch router (edge LSR), a device that initially adds or ultimately removes the label from the packet This router serves as the gatekeeper to and from the MPLS domain A Label that has been created by the Edge LSR is added to the frame header, which is subsequently used by label switch routers (LSR) to forward packets through the domain This header indicates what path the frame should travel to reach its destination This header format varies based upon the network media type For example, in an ATM network, the label is placed in the VPI/VCI fields of each ATM cell header In a LAN environment, the header is a "shim" located between the Layer and Layer headers Non-edge LSRs look at the frame, determine that there is a label embedded between Layers and 3, and then treat the frame according to the configuration in its Label forwarding information base (LFIB), a table created by the LSR describing where and how to forward frames with specific label values The label in the frame is just an index to a larger record in the LFIB, which consists of an incoming label and one or more subentries (including outgoing label, outgoing interface, and outgoing link-level information) If the incoming label finds a match then, for each component in the entry, the switch replaces the label in the packet with the outgoing label, replaces the link-level information (such as the MAC address) in the packet with the outgoing link-level information, and forwards the packet over the outgoing interface Each of the subsequent LSRs handles the frame in a similar manner until the frame reaches the egress Edge LSR, which then strips off all label information and passes a standard frame to the next hop Picture a series of LSRs (edge and core) interconnects, forming a physical path between two points Because the frame could be directed through the network based on contents of the LFIB and did not need to perform usual routing operation, the frame was handled more quickly Remember that label information can be carried in a packet in a variety of ways: As a small, shim label header inserted between the Layer and network layer headers Routing and Switching Written Qualification Exam (350-001) As part of the Layer header, if the Layer header provides adequate semantics (such as ATM) As part of the network layer header (such as using the Flow Label field in IPv6 with appropriately modified semantics) This means MPLS can be implemented over any media type, including point-to-point links, multiaccess links, and ATM Use of these types of control component(s) specific to a particular network layer protocol enable the use of label switching with different network layer protocols The label-forwarding component is independent of the network layer protocol How the LFIB is Propagated LSRs distribute labels using a label distribution protocol (LDP) A label binding associates a destination subnet to a locally significant label (Labels are locally significant because they are replaced at each hop.) Whenever an LSR discovers a neighbor LSR, the two establish a TCP connection to transfer label bindings LDP exchanges subnet/label bindings using one of two methods on with both LSRs must agree: Downstream Unsolicited Distribution - Disperses labels if a downstream LSR needs to establish a new binding with its neighboring upstream LSR For example, an edge LSR may enable a new interface with another subnet The LSR then announces to the upstream router a binding to reach this network Downstream-On-Demand Distribution - A downstream LSR sends a binding upstream only if the upstream LSR requests it For each route in its route table, the LSR identifies the next hop for that route It then issues a request (via LDP) to the next hop for a label binding for that route When the next hop receives the request, it allocates a label, creates an entry in its LFIB with the incoming label set to the allocated label, and then returns the binding between the (incoming) label and the route to the LSR that sent the original request When the LSR receives the binding information, the LSR creates an entry in its LFIB and sets the outgoing label in the entry to the value received from the next hop Quality of Service and Traffic Engineering Two important mechanisms are incorporated into MPLS to provide a range of QoS to packets passing through the domain: Classification of packets into different classes Handling of packets via appropriate QoS characteristics (such as bandwidth and loss) MPLS marks packets as belonging to a particular class during an initial classification using information carried in the network higher-layer headers A label corresponding to the resultant class is then applied to the packet Labeled packets could be handled efficiently by LSRs in their path without needing to be reclassified The Cisco Press book “MPLS and VPN Architectures” by Pepelnjak and Guichard is an excellent resource for learning more about MPLS IP Multicast IP Multicasting allows a device on the network to send a steam of information to a limited and defined group of hosts These hosts generally add and remove themselves to and from the data stream By this time you should be comfortable with the concepts behind Unicasts and Broadcasts, but just to reiterate: Unicast – A packet that has a specific destination address of a unique host in the IP network The packet is passed through the routed or switched network to its destination, or dropped if it is unreachable Broadcast - Packet that a single host sends to all IP hosts on the broadcast domain (usually a network segment) Keep in mind that every host that receives the broadcast interrupts its other work to process the packet Under normal circumstances, routers not forward broadcasts Routing and Switching Written Qualification Exam (350-001) Multicast traffic is a different beast It’s based on the concept of a group; a collection of recipient hosts which have “asked” to join a particular data stream; the group does not necessarily have any physical or geographical boundaries (depending on the network design), and potentially, group members can be located anywhere on the Internet Analogously, think of it as a newspaper subscription, or a cable TV drop; they don’t normally “just happen”, the recipient must make an effort, you know - express an interest Hosts interested in receiving a particular data flow join the IP Multicast Group using Internet Group Management Protocol (IGMP) Hosts must be a member of the group to receive the data stream Hosts join the group – they receive the traffic; if they don’t – they don’t The source then sends IP packets to an IP Multicast Group Address, then IP multicast routers forward out packets to interfaces that lead to members of the group This means one flow of traffic leaves the source, and the routers in between know how to process the packets to get them to a series of destinations that have either chosen or been defined as part of a multicast group The same information could be sent through broadcasts, but then every destination would be affected; or it could be sent through unicasts, but then each communication would require a separate data-stream, consuming valuable bandwidth With thousands of potential receivers, even low-bandwidth applications benefit from using IP Multicast High-bandwidth applications can often require a large portion of the available network bandwidth for just one single stream; the thought of multiple monster streams is what keeps a good Network Architect from spending time with their family As you can see, we have been describing a bandwidth-conserving technology that reduces traffic by simultaneously delivering a single stream of information to any number of destinations, without forwarding the traffic to disinterested destinations It delivers source traffic to multiple receivers without adding any additional burden on the source or the receivers, while using less network bandwidth than might otherwise be the case Popular IP Multicast applications include: Multimedia Conferencing – Geographically dispersed group meetings using audio/visual or audio-only communication, and often including electronic whiteboard applications Data Distribution – Reliably replicating data files from a central site to a number of remote locations, such as distributing price and product information from a central corporate headquarters to a number of remote sales locations Real-Time Data Multicasts – Pushing out real-time data to a number of subscribing hosts, such as stock or news ticker updates The benefits of IP Multicasting include significant savings in both bandwidth and server overhead because the source device only sends the material once Because of the reduced bandwidth utilization, there may also be a reduction of router CPU utilization, although the added load of handling multicast traffic may negate that under some circumstances Multicast packets are replicated in the network by Cisco routers enabled with Protocol Independent Multicast (PIM) and other supporting multicast protocols Configuration is fairly simple, and should be part of your knowledge arsenal if you intend to take the CCIE path later Because IP Multicasting is a one-to-many proposition, UDP is the layer-4 protocol of choice Problems related to unreliable packet delivery - such as lost packets, duplicate packets and lack of control over network congestion - exist, but can be reduced by proper network design Addressing Normal Unicast traffic is defined with a specific destination IP address that corresponds to a specific physical device This is not true of Multicast traffic, which forwards to a set of destinations, none of which has the specific IP address designated in the packet Remember when you first learned IP addressing, and you used A, B and C-class addresses? Well, the instructor didn’t mention it to you - but there was also a D-class set of addresses, and that’s what is used for multicast addressing Routing and Switching Written Qualification Exam (350-001) Multicast IP addresses (D-class addresses) are in the range of 224.0.0.0 to 239.255.255.255, meaning the first four bits of the address are 0x1110 These addresses are administered by the Internet Assigned Number Authority (IANA), and tightly controlled they are Don’t count on grabbing a few addresses in case you ever need them; with that limited range of addresses available, they are very stingy about assigning them One interesting outcropping of this is that there is now a DHCP-like service running that allows the entire Internet community to share the remaining unassigned range of IP multicast addresses dynamically (please notice I said DHCP-like, not actual DHCP) The IANA has put aside 239.0.0.0 through 239.255.255.255 for private multicast domains, much like the reserved IP unicast ranges (192.168.x.x, 172.16.x.x and 10.x.x.x) When you are developing an internal application that will remain within the boundaries of your network, these should be the addresses you choose to implement The addresses in the range of 224.0.0.0 to 224.0.0.255 have been put aside by the IANA for use by routing protocols on the local network segment, meaning routers have been programmed not to forward them, regardless of what the TTL value is Reserved addresses in this range include: Address Usage 224.0.0.1 All Hosts 224.0.0.2 All Multicast Routers 224.0.0.4 DVMRP Routers 224.0.0.5 OSPF Routers 224.0.0.6 OSFP Designated Routers 224.0.0.7 ST Routers 224.0.0.8 ST Hosts 224.0.0.9 RIP2 Routers 224.0.0.10 IGRP Routers 224.0.0.12 DHCP Server/Relay Agent 224.0.0.13 All PIM Routers Translate Multicast Addresses into Ethernet MAC addresses IANA maintains a block of Ethernet MAC addresses from 0100.5e00.0000 through 0100.5e7f.ffff as the range of available Ethernet MAC address destinations for IP Multicast This allocation allows 23 bits in the Ethernet Address to correspond to the IP Multicast group address As we’ve already discussed, Multicast IP addresses are Class-D addresses which are in the range 224.0.0.0 to 239.255.255.255 (first octet equal to binary 11100000 through 11101111) They are also referred to as Group Destination Addresses (GDA) For each GDA there is an associated MAC address This MAC address is formed by appending 01-00-5e to the last 23 bits of the GDA, translated into hex Remember that since only the last 23 bits of the GDA address is used, the second octet of the address can have either of two values and still be correct For example: A GDA of 229.119.213.55 translates to a MAC of 01-00-5e-77-d5-37 Here’s why… Decimal IP address = 229.119.213.55 Routing and Switching Written Qualification Exam (350-001) Binary equivalent = 11100101.01110111 11010101.00110111 Last 23 bits = 1110111 11010101.00110111 Hex equivalent of last 23 bits = 77-d5-37 Append with 01-00-5e = 01-00-5e-77-d5-37 Internet Group Management Protocol (IGMP) and Cisco Group Management Protocol (CGMP) In order to manage IP multicasting, allow directed switching of multicast traffic, and dynamically configure switch ports so that IP multicast traffic is forwarded only to the appropriate ports Cisco switches use: Internet Group Management Protocol (IGMP) - A standard protocol designed to manage the multicast transmissions passed to routed ports by dynamically registering individual hosts in a multicast group Hosts identify group memberships by sending IGMP messages to their local multicast routers Under IGMP, routers listen to IGMP messages and periodically send out queries to discover which groups are active or inactive on a particular subnet One of the problems with this protocol is if a VLAN on a switch is set to receive, all the workstations on that VLAN will get the multicast stream Cisco Group Management Protocol (CGMP) - A Cisco proprietary protocol designed to control the flow of multicast streams to individual VLAN port members while limiting the impact on the switch CGMP requires IGMP to be running on the router IGMP There are two versions of IGMP Version is defined in RFC 1112 and provides just two different types of IGMP messages: Membership Reports - Hosts send out IGMP Membership Reports corresponding to a particular multicast group to indicate they are interested in joining that group Membership Queries - The router periodically sends out an IGMP Membership Query to verify that at least one host on the subnet is still interested in receiving traffic directed to that group When there is no reply to three consecutive IGMP Membership Queries, the router will stop forwarding traffic directed toward that group IGMP Version is defined in RFC 2236.The primary difference is the inclusion of a Leave Group message, which allows hosts to take the initiative and actively communicate to the local multicast router that they no longer wish to be part of the multicast group The router then sends out a group specific query and determines if there are any remaining hosts interested in receiving the traffic If there are no replies, the router will time out the group and stop forwarding the traffic This can greatly reduce the leave latency found with IGMP Version The default behavior for a Layer switch would be to forward all multicast traffic to every port that belongs to the destination LAN on the switch Routing and Switching Written Qualification Exam (350-001) Basically, if one host on a VLAN wants to see the multicast, everybody on the VLAN gets it Since the purpose of a switch is to limit traffic to just the ports that need to see it, this is not a desirable behavior There are two methods to deal the problem - Cisco Group Management Protocol (CGMP) and IGMP Snooping CGMP CGMP and IGMP software components run on both the Cisco routers and Cisco Catalyst switches Together they allow these switches to leverage IGMP information on Cisco routers to make layer-2 (switching) forwarding decisions With CGMP, IP Multicast traffic is delivered only to those Catalyst switch ports that are interested in the traffic; ports that have not explicitly requested the traffic will not receive it When the CGMP/IGMP-capable router receives an IGMP control packet, it processes it as it would any other IGMP request, and then creates a CGMP message, which it then forwards to the switch These can either be “join” or “leave” messages, depending on what the host is asking for The switch receives the CGMP message and then modifies the port status in its CAM (Content Addressable Memory) table for that multicast group All subsequent traffic directed to this multicast group will be forwarded to the port The router port is also added to the entry for the multicast group It’s important to note that Multicast routers are required to monitor all multicast traffic for every group, since the IGMP control messages look just like regular multicast traffic With CGMP, the switch only has to listen to CGMP “Join” and “Leave” messages from the router The rest of the multicast traffic is forwarded using its CAM table as normal The router carries the load Please note that if there is a spanning-tree topology change, the CGMP/IGMP-learned multicast groups on the VLAN are purged and the CGMP/IGMP-capable router must generate new multicast group information If a CGMP/IGMPlearned port link is disabled, the corresponding port is removed from any multicast group CGMP/IGMP-capable routers send out periodic multicast group queries, so if a host wants to remain in a multicast group, it must respond to the query If, after a number of queries, the router receives no reports from any host in a multicast group, the router sends a CGMP/IGMP command to the switch to remove the group from the forwarding tables CGMP’s fast-leave-processing allows the switch to detect IGMP version-2 leave messages sent to the allrouters multicast address by hosts on any of the supervisor engine module ports Remember that CGMP must be configured on both the multicast routers and the layer-2 switches and that CGMP is Cisco proprietary IGMP Snooping IGMP Snooping is another technique to avoid sending multicast traffic to disinterested switched Ethernet ports on a Cisco switch It requires the LAN switch to examine, (“snoop” through) network layer information in the IGMP packets sent between the hosts and the router When the switch hears the IGMP Host Report from a host for a particular multicast group, the switch adds the host's port number to the associated multicast table entry When the switch hears the IGMP “Leave” Group message from a host, it removes the host's port from the table entry This obviously puts the burden of processing on the switch, creating a potential performance impact on low-end switches with limited CPU horsepower Many high-end switches have special ASICs that can perform the IGMP checks in hardware Routing and Switching Written Qualification Exam (350-001) Multicast Distribution Trees Multicast capable routers use distribution trees to control the paths used by traffic as it traverses the network There are two basic types of multicast distribution trees: Source Trees - A source tree is the simplest type of a multicast distribution tree, with its root at the source and branches forming a spanning tree through the network to all the receivers Source trees have the advantage of creating the optimal path between the source and the receivers, and are therefore often referred to as “shortest path trees” The size of the multicast routing table can create problems on larger multicast networks Shared Trees - Shared trees use a predefined shared root, called a Rendezvous Point (RP), which allows the routers to know little about the overall network layout, lowering the overall memory requirements for a network that only allows shared trees Because multicast group members can join or leave at any time, distribution trees must be dynamically updated Protocol Independent Multicast (PIM) PIM is used to forward multicast packets through a network It must be enabled for a Cisco interface to perform IP multicast routing Enabling PIM on an Interface also enables IGMP operation on that interface It can be configured in Dense, Sparse or Dense-spare modes Dense is used when most hosts have plenty of bandwidth and wish to be part of the multicast Sparse is used when there is a lesser percentage of hosts that wish the service, RP’s are used, or if there are expensive WAN links that not require the multicast broadcast PIM uses whichever unicast routing protocol is in place to populate the unicast routing table, including EIGRP, OSPF, BGP or even just static routes; that’s why it is considered IP routing protocol independent (thus the name) The information gained from the unicast routing process is used to support the multicast forwarding function by performing Reverse Path Forwarding (RPF) functions instead of building up a separate multicast routing table This enables routers to correctly forward multicast traffic down a distribution tree by using existing unicast routing table information to determine upstream and downstream neighbors A router will only forward a multicast packet if it is received on the upstream interface RPF check ensures that the distribution tree is free of loops For PIM to work, it must be in one of these modes (remember that PIM is not enabled by default; and does not have a default mode): PIM Dense Mode (PIM-DM) - Dense-mode interfaces are always added to the table Dense mode is used when multicast group members are densely distributed throughout the network and there is plenty of bandwidth available Dense mode PIM floods the multimedia packet to all routers and prunes routers that not support members of that particular multicast group This should be considered a “push” model, used to flood multicast traffic to every corner of the network PIM-DM can only support source trees; it cannot be used to build a shared distribution tree PIM Sparse Mode (PIM-SM) - Sparse-mode interfaces are added to the table only when periodic “join” messages are received from downstream routers, or when there is a directly connected member on the interface Sparse mode is used when members are more spread out and there is limited bandwidth available Sparse mode PIM relies on rendezvous points (RP) This should be considered a “pull” model, building its groups through requests from specific destinations The explicit join mechanism prevents unwanted traffic from flooding slow WAN links, and minimizing other network bandwidth utilization PIM-SM uses a shared tree to distribute its information Sparse-dense Mode - These interfaces are treated as dense mode if the group is in dense mode, or in sparse mode if the group is in sparse mode This configuration option allows individual groups to run in either sparse or dense mode, depending on whether RP information is available for that specific group If the router learns RP information for a particular group it will be treated as sparse mode, otherwise that group will be treated as dense Sparse-dense mode provides a great deal of flexibility for the Network Architect A significant difference between Dense and Sparse modes is that a dense mode router assumes all other routers are willing to forward multicast packets for a group, while a sparse mode router requires an explicit request for the traffic Routing and Switching Written Qualification Exam (350-001) PIM-Spare Mode Mechanics In dense mode, multicast traffic is initially flooded to all segments of the network Routers with no downstream neighbors or directly connected receivers prune back the unwanted traffic In sparse networks, only those segments with active receivers that have explicitly requested multicast data will be forwarded the traffic Rendezvous points (RP) (described below) provide the mechanism for providing multiple distribution points; the source feeds the RP with one stream, which is then redistributed to the destinations within the various RP domains PIM-SM Joining & Pruning A Multicast join message is sent from the router to the Rendezvous Point (RP) when a new device requests the multicast group and the router is not already receiving it A multicast group is requested to be pruned when there are no more devices receiving the group IP Multicast Routing Table (mroute) The IP Multicast Routing table is known as the “mroute” table This table shows the multicast groups the router can access with PIM-SM, the rendezvous point, and the interfaces for the group Distribution Trees Multicast-capable routers create distribution trees to control the path through the network The two basic types of multicast distribution trees are: Source Trees - These are the simplest form of a multicast distribution tree, where the root is the source of the multicast tree and the branches form a spanning tree through the network to the receivers Because this tree uses the shortest path through the network, it is also referred to as a shortest path tree (SPT) Shared Trees - Unlike source trees that have their root at the source, shared trees use a single common root placed at some chosen point in the network This shared root is called the rendezvous point (RP) Rendezvous Points The most significant difference between PIM sparse and dense mode configurations is the requirement for Rendezvous Points (RP) to be defined in sparse networks This acts as the meeting place for sources and receivers of multicast data The sources send their traffic to the RP, and it is then forwarded to receivers down a shared distribution tree By default, when the first hop router of the receiver learns about the source, it will send a join message directly to the source, creating a source-based distribution tree from the source to the receiver Since by default the RP is only needed to start new sessions with sources and receivers, it experiences little additional overhead from traffic flow or processing In PIM-SM version 1, all routers directly connected to sources or receivers (leaf routers) are manually configured with the IP address of the RP; for this reason this type of configuration is also known as a “static RP” configuration This isn’t much of a problem in a small network (like a lab exam), but it can create obvious problems in a large, complex network PIM-SM version has an Auto-RP feature that automates the distribution of group-to-RP mappings in a PIM network The advantages of this are: Not having to configure a static RP address on every router Routing and Switching Written Qualification Exam (350-001) Changes need only be configured on the RP routers, not on all the leaf routers The ability to “scope” the RP address within a domain, giving it an area of the network to cover Scoping can be achieved by defining the time-to-live (TTL) value allowed for the Auto-RP advertisements Bootstrap Router (BSR) PIM version supports something called a Bootstrap router (BSR) A BSR is an alternative to using an the AutoRendezvous Point (Auto-RP) feature BSR is detailed in RFC 2362 (PIM Version 2) To use BSR, you select BSR Candidate routers These routers have priorities that you configure The router with the highest priority becomes the bootstrap router The Cisco Press book “Developing IP Multicast Networks” by Beau Williamson is an excellent resource for Multicast Networking Reference The following text was used as a reference in the creation of this Cramsession: CCIE Routing and Switching Exam Certification Guide by A Anthony Bruno, ISBN 1-58720-53-8 [...]... manufacturers Routing and Switching Written Qualification Exam (350-001) The second part of the MAC address, the last three bytes (24 bits), is a unique identifier burned into the device by the manufacturer from the series issued to it General Routing Concepts Link-State – Link state routing protocols use a complex algorithm to calculate the best route Each router calculates its own routing table Examples... Link-State routing protocols are OSPF and NLSP Distance Vector – Routing protocols that use hop counts to select the best path Examples are RIP and IGRP Distance vector routing protocols are best for small networks Switching vs Routing – switching works at OSI Layer 2 (data-link) by keeping track of L2 addresses and sending out frames to only the ports where the destination MAC address has been seen Routing, ... take advantage of summarization: The larger the routing table, the more memory is required because every entry takes up some of the available memory The routing decision process may take longer to complete as the number of entries in the table are increased Routing and Switching Written Qualification Exam (350-001) An added benefit of reducing the IP routing table size is that it requires less bandwidth... Lookback addresses 0:0:0:0:0:0:0:1 ::1 IP Routing Routing Protocol Concepts Routing protocols provide dynamic network information to the routers that are part of the domain, and represent one of the most important areas for a Network Engineer to master Distance-Vector Routing Protocols Protocols that are designed to periodically pass the full contents of their routing tables to all of their immediate... include slow convergence, routing loops, counting to infinity problems, and excessive bandwidth utilization from the size and repetition of the updates The two common Distance Vector protocols are the Routing Information Protocol (RIP), and Cisco's proprietary Interior Gateway Routing Protocol (IGRP), which uses bandwidth and delay Link State Routing Protocols Link State Routing Protocols develop and... conserves bandwidth for the transmission of user data Routing and Switching Written Qualification Exam (350-001) Cisco's proprietary Enhanced Interior Gateway Routing Protocol (EIGRP) is the most common Hybridized routing protocol (and the only one I’ve ever heard of) It was designed to combine the best aspects of distance-vector and link-state routing protocols without incurring any of the performance... configure a vty password By default, there Routing and Switching Written Qualification Exam (350-001) are 5 of these lines (zero through four) To configure a vty password, on all 5 lines, you would type: Router(config)# line vty 0 4 Router(config-line)# login Router(config-line)# password cisco General Networking Theory OSI Models Most people who attempt the CCIE Written have either gone through the CCNA... routes from a routing protocol that supports VLSM (such as EIGRP or OSPF) into a routing protocol that does not (such as RIPv1 or IGRP) you might lose some routing information Some important requirements exist for summarization: Multiple IP addresses must share the same high-order bits Since the summarization takes place on the loworder bits, the high-order bits must have commonality Routing tables... routing measure of distance The source node does not need to care about how to pick the closest destination node, as the routing system will figure it out (in other words, the source node has no control over the selection) The set of destination nodes is identified by an Anycast address Valid Ipv6 Unicast or Anycast addresses: 1080:0:0:0:8:800:200C:417A 1080::8:800:200C:417A Routing and Switching Written. .. environment will have trouble learning about each other For these situations, you may choose to disable split-horizon Routing Loops - Routing loops occur when the routing tables of some or all of the routers in a given domain route a packet back and forth without ever reaching its final destination Routing loops often occur during route redistribution, especially in networks with multiple redistribution points