origins and understanding of frame relay frame relay has emerged to provide higher throughput,...
TRANSCRIPT
Origins and Understanding of Frame Relay Frame relay has emerged to provide higher throughput, higher
bandwidth, more cost-effective packet-style data transport, and take advantage of new digital and fiber-optic transmission facilities.
Frame relay combines the advantages of both time division and statistical multiplexing on a single-access circuit, while maintaining low end-to-end network latency
Frame relay allows speeds up to T1 (theoretically up to 45 Mbps) while switching frames of fixed or variable size over PVCs and SVCs
Frame relay standards are derived from the ISDN Link Access Procedure for the D-channel
Frame Relay Defined A FR user –access port connects to the FR network-access port
through the use of a FR user access circuit, also called a User-to-Network Interface (UNI)
One or multiple Permanent Virtual Circuits (PVCs) reside within a single UNI.
Each PVC is bidirectional and each direction has an assigned Committed Information Rate (CIR).
Each endpoint of the PVC has an identifier called a Data Link Connection Identifier (DLCI)
Refer to Figure 10.1 (p. 364)
FR User-Access Ports and Circuits (FR UNIs) The FR user access port is a physical port on the Customer
Premises Equipment (CPE) such as a router The FR user-access port is connected to a single FR access
circuit, typically a digital DS0, fractional T1, or a DS1 This FR access circuit is then connected to a FR network-
access port, which is the physical port on a FR switch at the service provider’s premises
This access circuit is named User-to-Network Interface (UNI) Refer to Figure 10.2 (p. 364)
Permanent Virtual Circuit (PVC) Each FR UNI supports one or more PVCs PVCs are virtual circuits, or virtual private lines, provisioned
point-to-point from one FR user-access port to another FR user-access port
While each end of the PVC will terminate on a FR switch port, the user sees one end-to-end PVC from user port to user port.
Refer to Figure 10.3a (p. 366) The user devices view a PVC from FR user-access port to user-
access port, when in reality they are defined between two FR access ports
Permanent Virtual Circuit (PVC) (Continue…) Any data transmitted over PVC arrives in exact sequence as it
was sent, and end-to-end security of the circuit is the same PVCs are switched by FR switches within the FR network Refer to Figure 10.3b (p. 366) Refer to Figure 10.4 (p. 366) PVC does not consume bandwidth when it is not transmitting
data. Each FR access circuit can contain up to 1024 PVCs in theory,
but service providers and CPE typically support a maximum of one hundred
Committed Information Rate (CIR) CIR is a quality-of-service measurement that provides a
“statistically guaranteed” minimum rate of throughput to its PVC at any one period of time
CIR rates are unidirectional, in that each PVC has a CIR rate for each direction
Refer to Figure 10.5 (p. 368) CIRs that are able to assign different rates to each direction of
the PVC are called unidirectional or simplex CIRs
Data Link Connection Identifier (DLCI) DLCI provides each PVC with a unique identifier at both the
CPE device and the FR switch
Frame Relay Functions – Putting it all together Frame relay provides an upgrade to existing packet switching
technology, by supporting speeds up to DS3 (45 Mbps) Frame relay supports PVCs for static user configurations and
SVCs for the infrequent user who requires virtual circuits-on demand.
Frame relay is a service that delivers frames in order with high probability and can operate effectively only on low error-rate media
Frame relay acts as a data link protocol to higher layer protocols, such as TCP/IP
Frame Relay Functions – Putting it all together (Continue…)
Frame relay virtual circuits (PVCs and SVCs) may be point-to-point or point-to-multipoint (called multicast)
Frame relay virtual circuits may be arranged into closed user groups for security purposes
Frame Relay Access to a FR Network Frame relay defines both a packet-access technique which
provides bandwidth-on-demand and a data link OSIRM layer 2 interface
The interface transmits frames to a public or private network service and on to a destination interface over a PVC.
The end points of the PVCs are defined by a source and destination address or Data Link Connection Identifier (DLCI)
As an interface, Frame relay operates over BRI and PRI ISDN, V-series, DDS and DDN, fractional T1, X.21, T3, and even SONET
Frame Relay Access to a FR Network (Continue…)
Refer to Figure 10.7 (p. 371) The frame relay switch can either be at the LEC PoP, IXC PoP,
or service provider location. The local loop is typically DS0, fractional T1, or T1 Frame Relay Access Device or Assembler/Disassembler
(FRAD) is used to combine mixed subrate protocols which are aggregated into a single frame relay access circuit and transmitted to the frame relay network
Refer to Figure 10.8 (p. 371)
Frame Relay Access to a FR Network (Continue…)
Frame relay access provides a cost-effective solution for the transport of bursty data, such as LAN traffic.
FR’s statistical multiplexing capability makes it an ideal choice for aggregation of multiple private lines up to T1 speeds
Multiple logical circuits can be combined within a single physical circuit
Frame relay as a network access offers the following benefits Equipment and local loop services Maximizes link efficiency True international standard
Equipment and Local Loop Savings By allowing multiple users access to a single shared physical
access circuit, tremendous savings in network interface equipment, local loops, and long distance IXC bandwidth costs can be achieved
Refer to Figure 10.11 (p. 374) Refer to Figure 10.12 (p. 375) Refer to Figure 10.13 (p. 375) Refer to Figure 10.14 (p. 376)
Maximizes Link Efficiency FR makes maximum use of physical circuit bandwidth by
statistically multiplexing multiple PVCs over a single physical circuit.
Frame Relay as a Signaling Protocol The OSIRM layer 2 is split by frame relay standards into two
major areas: core services and user-defined services Benefits of using frame relay are
In-band CPE management - Transparent to higher layer protocols In-band link management - Improved performance over packet
switching Protocol flexibility - Flexibility of bandwidth allocation
Frame Relay as a Network Service Frame relay has become one of the primary LEC and IXC data
service offerings Frame relay service does provide the concentration and
statistical multiplexing of X.25 packet switching, while providing the short delay and high speed switching of TDM multiplexers
Permanent Virtual Circuits (PVCs) and Switched Virtual Circuits (SVCs) are established from one-to-one or many-to-one (multicast) end points, with a dynamic route through the “cloud”
Frame Relay as a Network Service (Continue…) A typical frame relay public data transport network will support a variety of
user access devices, including T1/E1 multiplexer, bridge, router, gateway, front-end processor, an X.25 packet switch, and a Frame Relay Access Device or Assembler/Disassembler (FRAD)
Refer to Figure 10.16 (p. 380) Frame relay as a network service offers the following benefits:
Circuit savings - Higher circuit availability Higher network availability - Prevention from technology discontinuity Latency increases or reductions – Dynamic circuit and network architecture Lower WAN costs - Fills the need for high-speed LAN-to-
WAN connectivity One network – multiple protocols - Managed service and guarantee of
availability
Frame Relay Protocol Structure in Relation to the OSIRM
Frame relay transport comprises only the first two layers of the OSI model, the physical and data link layers
Refer to Figure 10.19 (p. 385) The physical layer interface can range from a DS0, through
fractional T1, up to and including a full T1 Layer 2 utilizes the ITU-T/CCITT link access procedure (LAP-
D) data link layer protocol Frames are transmitted between nodes at the OSI layer 2 data
link layer
Frame Relay Protocol Structure in Relation to the OSIRM (Continue…)
Frame relay checks for frame validity with the Frame Check Sequence (FCS) and frames are discarded if in error
FR nodes establish permanent virtual circuits and route the data through this point-to-point serial connection
Frames are routed by destination addresses (DLCI) Refer to Figure 10.20 (p. 386) FR switches operate at layer 2, while the transport of data
across the UNI operates at layer 1 Refer to Figure 10.21 (p. 387)
Layer 2 Protocol Structure Details Frame relay service is concerned with two logically separate
levels of the data link layer, defined as the control plane (C-plane) and the user plane (U-plane)
Refer to Figure 10.22 (p. 388) The U-plane provides the data transport of the user data via the
physical access line through logical links The control plane is involved with reporting on the status of
PVCs, or the establishments of SVCs The C-plane can perform frame relaying by two methods:
Virtual Calls (VCs) and Permanent Virtual Connections (PVCs)
Layer 2 Protocol Structure Details (Continue…) The U-plane is split into core functions and user-selectable
terminal functions The C-plane is also split into layer 2 and layer 3 services, or the
procedures necessary for signaling
Core Services Core services correspond to the U-plane functionality, which
defines user-selectable frame-relaying services Refer to Figure 10.25 (p. 391)
Procedural Sublayer Services The procedural sublayer defines procedures for data transport
from the user device to the network and between devices. This is where true signaling information is managed
Transmission Protocol TheoryOverview The high throughput of frame relay is achieved by removing
correction and foregoing addressing overhead functions found resident in traditional packet-switching technologies
Frame relay provides fast reconnect and statistical multiplexing Highly reliable digital facilities or fiber-optic transmission are
preferred in the frame relay environment because virtual error-free transmission media is essential
Frame relay differs from TDM and FDM multiplexer networks in that the statistical properties of frame relay allocate bandwidth only as needed
Refer to Figure 10.26 (p. 393) With frame relay access, each user (protocol) is assigned a
virtual channel Frame relay networks can be much more efficient compared to
private line networks based on the number of access circuits Refer to Figure 10.27 (p. 394) Depending on the specific vendor implementation, intermediate
nodes often do not perform any packet disassembly or error correction
Refer to Figure 10.28 (p. 396)
Basics of SAP and DLCI ITU-T/CCITT Q.920 defines the terms and basic concepts of
DLCI data link addressing. The Service Access Point (SAP) is the logical-level data link
interface from the user to the network. The SAP provides services to layer 3 protocols. There are
multiple data link connection endpoints associated with each SAP, and at the link layer, these are referred to as Data Link Connection Identifiers or DLCIs.
Refer to Figure 10.29 (p. 397)
Frame Format The frame format used by frame relay services is a derivative
of the ISDN Link Access Protocol D-channel (LAP-D) framing structure
Refer to Figure 10.31 (p. 398) Refer to Figure 10.32 (p. 398)
Address Field Structure The Data Link Connection Identifier (DLCI) is split into two
fields, together forming a 10-bit DLCI that identifies up to 1024 virtual circuits per interface
Address Field Structure (Continue…) This DLCI identifies the logical channel connection within the
physical channel or port for a predetermined destination The DLCI may have local significance on an access circuit or
global significance to the FR network Global DLCI assignment is when each user CPE device must
have a separate DLCI for each destination. This limits the size of a frame relay network to approximately 1000 nodes
FR service providers use local significant DLCI assignment where the DLCI is significant to the FR access port only
DLCI numbers may be used on each FR access circuit across the network
Address Field Structure (Continue…) Almost all North American frame relay implementations use
local significant DLCI assignment method The Command/Response (C/R) bit is not used at this time The Forward Explicit Congestion Notification (FECN) bit is a
toggle that tells the remote user that network congestion was encountered by the frame transmitted across the physical media, and that the user should take action to prevent data loss
The Backward Explicit Congestion Notification (BECN) bit works the same, but notifies the sender of congestion in the data on the returning path
Address Field Structure (Continue…) The Discard Eligibility (DE) bit, when set at 1, indicates that
the frame should be discarded during congestion conditions, as opposed to discarding other frame with a higher priority (those set at 0)
The Extended Address (EA) bits act as address field delimiters, set at 0 and 1, respectively.
Each user CPE device with multiple logical and physical ports must have a separate DLCI for each destination on the egress port it wants to transmit to.
These DLCIs are built into the switching/routing tables of each CPE and switching device on the network
Data Field or Payload Structure The data field or “payload” structure can vary in size up to
4096 or 8188 octets long. The data can be either pure data - when using a direct
connection to a device that provides a frame relay interface - or it can be encapsulated packets of a different protocol
Refer to Figure 10.35 (p. 403)
Frame Check Sequence (FCS) The FCS field assures the data integrity of the frame. If there is
an error, the frame is discarded.
Frame Relay Addressing A Data Link connection Identifier (DLCI) provides each PVC
with an addressing scheme. Each point of a PVC is assigned a DLCI
Each frame within a PVC is sent from an originating DLCI to a destination DLCI where the frame check sequence (FCS) is verified
If the frame does not pass the FCS, it is simply discarded with no indication to the network or user.
If the frame does pass the FCS, the DLCI is located in a routing table; routing tables then match addresses, either DLCI to DLCI, or DLCI to IP
Frame Relay Addressing (Continue…) If the DLCI has been predefined for this PVC, the frame will be
routed to its final destination. If the DLCI has not been defined for this PVC, it is discarded. If it is the destination node, the frame is passed through the
logical and physical port to the user Each FR access circuit can contain up to 1024 PVCs. Some of
these are dedicated to LMI, leaving 992 usable DLCIs Refer to Figure 10.36 (p. 405) Refer to Figure 10.37 (p. 406)
Frame Handling and Switching with ISDN FR Access When using an ISDN implementation of frame relay, the Frame
Handlers (FHs) and Remote Frame Handlers (RFHs) perform much of the frame-relaying service between the physical ports and the mapping of the logical DLCIs between all ports in a group.
Refer to Figure 10.38 (p. 407) The frame handler will also
Map in-bound to out-bound DLCI Perform FCS and correct for retransmission Discard corrupted frames Write out-bound DLCI value into the frame-address field Coordinate transport of frame out of the physical channel
Logical Channel Multiplexing via Frames Through the use of the DLCI addressing, multiple user logical
data streams can be multiplexed and demultiplexed within the same physical data channel
Each physical channel can contain up to 1023 logical channels, each identified by a DLCI value
These multiplexed users are assembled into frames and transmitted across the network.
These frames retain their order of transmission and reception. Each protocol is negotiated during the call establishment procedure
Refer to Figure 10.39 (p. 408)
User Interface By eliminating the need for multiple access lines by using a
single access into a switched infrastructure, whether a private or public frame relay network, users can be reduce a significant portion of networking costs.
The actual physical user interface is typically an RS-449 or V.35 connection to a router or switch, although with the drop in local BRI access charges ISDN interfaces are fast being deployed.
With frame relay, the user can minimize the number of interfaces to the network by using multiple V.35, or four-wire, if a CSU/DSU is needed
User Applications Typical synchronous traffic might include long network connection
times, excessive call setup and takedown times, long transmission sessions, nonbursty traffic patterns, and PVC connections
Make sure the applications are well matched to frame relay
Interface Signaling Transmission equipment such as CSUs, DSUs, and other
channel-conditioning devices may require in-band or out-of-band signaling.
This should be transparent to the frame relay transmission, however, while providing maximum throughput, line efficiency, and minimum response time degradation and delay
PVC Management When a Permanent Virtual Circuit (PVC) is established between
two physical ports and one or multiple DLCI addresses are established over this link, there is a need for both the network access device (user) and the network switching device (provider) to manage the status of the link
PVC management is defined by ANSI, ITU-T, and the LMI extensions. These specifications define three main areas of PVC management: PVC status signaling DLCI verification physical interface keep-alive heartbeat
The Local Management Interface (LMI) Extension The LMI extension defines a protocol for managing the frame
relay access circuit from FR CPE to the FR public network switch.
The LMI provides a keep-alive signal between the FR CPE and the FR network access port, makes the initial frame relay circuit and equipment configuration simpler by allowing notification of connectivity, and provides a status report for active or deactivated DLCIs
Refer to Figure 10.40 (p. 411) The LMI extensions define DLCI address number 1023 as the
LMI address
The Local Management Interface (LMI) Extension (Continue…)
There are two types of messages: STATUS_ENQUIRY: is sent by the user device to request a status
message from the network STATUS: is sent from the network to the user device telling the status
of PVCs in the network connected to that user device
Information elements can contain a KEEP_ALIVE_SEQUENCE which proves that both the user device and the network element are active
The PVC_STATUS gives the configuration and status of an existing PVC
The Local Management Interface (LMI) Extension (Continue…)
The REPORT_TYPE to indicate either the type of inquiry requested by the user device or the status message content.
Refer to Figure 10.42 (p. 413)
Cisco
Managing a Cisco Internetwork
Objectives
Back up a Cisco IOS to a TFTP server Upgrade or restore a Cisco IOS from a TFTP server Back up and restore a Cisco router configuration using a
TFTP server Use the Cisco Discovery Protocol to gather information
about neighbor devices Create a host table on a router and resolve host names to IP
addresses Verify your IP host table Use the OSI model to test IP
Cisco Router Components
Bootstrap Brings up the router during initialization
POST Checks basic functionality; hardware & interfaces
ROM monitor Manufacturing testing & troubleshooting
Mini-IOS Loads Cisco IOS into flash memory
RAM Holds packet buffers, routing tables, & s/w Stores running-config
Cisco Router Components
ROM Starts & maintains the router
Flash Memory Holds Cisco IOS Not erased when the router is reloaded
NVRAM Holds router (& switch) configurations Not erased when the router is reloaded
Configuration Register Controls how the router boots up
Boot Sequence
#1: Router performs a POST#2: Bootstrap looks for & loads the Cisco IOS#3: IOS software looks for a valid configuration file#4: Startup-config file (from NVRAM) is loaded
If startup-config file is not found, the router will start the setup mode
Configuration Registers
Register 16-bit software written into NVRAM Loads from flash memory & looks for the startup-config file
Configuration Register Bits 16 bits read 15-0, from left to right default setting: 0x2102
Register 2 1 0 2
Bit number 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Binary 0 0 1 0 0 0 0 1 0 0 0 0 0 0 1 0
NOTE: 0x means the digits that follow are in hexadecimal
Configuration & Boot Field Meanings
Checking the Register Value
Router#sh version
Cisco Internetwork Operating System Software
IOS ™ C2600 Software (C2600-I-M), Version 12.0(3)T3
RELEASE SOFTWARE (fc1)
[output cut]
Configuration register is 0x2102
Changing the Configuration Register
Force the system into the ROM monitor mode Select a boot source & default boot filename Enable or disable the BreakBreak function Set the console terminal baud rate Load operating software from ROM Enable booting from a TFTP server
Changing the Configuration Register
Router(config)#config-register 0x0101
Router(config)#^Z
Router#sh ver
[output cut]
Configuration register is 0x2102 (will be 0x0101 at next reload)
Recovering Passwords
Step #1: Boot the router & interrupt the boot sequence by performing a break
Step #2: Change the configuration register to turn on bit 6 (0x2142)
Step #3: Reload the router
Step #4: Enter the privileged mode
Step #5: Copy the startup-config to running-config
Step #6: Change the password
Step #7: Reset the configuration register to the default value
Step #8: Reload the router
Recovering Passwords
Step #1: Boot the router & interrupt the boot sequence by performing a break
Warning: Windows NT’s default HyperTerminal program will not perform the break
How to Simulate a Break Key Sequence Connect to the router with the following terminal settings:
1200 baud rate No parity 8 data bits 1 stop bit No flow control
You will no longer be able to see any output on your screen. This is normal.
Reload the router and press the spacebar for 10-15 seconds. This generates a signal similar to the break sequence.
Disconnect your terminal and reconnect with a 9600 baud rate. You should now be in ROM Monitor mode; rommon>
Recovering Passwords
Step #2: Change the configuration register to turn on bit 6 (0x2142)
rommon>confreg 0x2142You must reset or power cycle for new config to take effect
Step #3: Reload the router Type reset
The router will reload & ask if you want to enter setup mode Answer NO
Step #4: Enter the privileged modeRouter>enableRouter#
Recovering Passwords
Step #5: Copy the startup-config to running-configRouter#copy startup-config running-config
Step #6: Change the passwordRouter#config tRouter(config)#enable secret ciscocisco
Step #7: Reset the configuration register to the default value
Router(config)#config-register 0x2102
Step #8: Reload the router
Backing up & Restoring the Cisco IOSIOS
Before you upgrade….. Copy the existing IOS to a TFTP host!
Verify Flash MemoryRouter#sh flashSystem flash directory:File Length Name/status 1 8121000 c2500-js-1.112-18.bin[8121064 bytes used, 8656152 available, 16777216 total]16384K bytes of processor board System flash (Read ONLY)Router#
Backing up the Cisco IOSIOS
#1: Ensure you have good connectivity to the TFPT host
Router#ping 192.168.0.120
#2: Copy the IOS from flash to the TFTP host
Router#copy flash tftp The TFTP host must have a default directory specified
Restoring or Upgrading the Cisco IOS
#1: Ensure you have good connectivity to the TFTP host
Router#ping 192.168.0.120
#2: Copy the IOS from the TFTP host to flash
Router#copy tftp flash The TFTP host must have a default directory specified Copying the IOS from a TFTP host to flash requires a router reboot
Backing up the Configuration
Step #1: Verify the Current Configuration Router#sh run
Step #2: Verify the Stored Configuration Router#sh start
Verify available memory
Step #3: Copy running-config to NVRAM Router#copy run start
Router#sh start
Step #4: Copy running-config to a TFTP host Router#copy run tftp A second backup
Restoring the Configuration
Used when… You need to copy the startup-config to the
running-config Errors made in editing the running-config
Changes made at the TFTP host need to be copied to the running-config or startup-configRouter#copy tftp run or Router#copy tftp start
NOTE: The configuration file is ASCII. Any text editor will enable changes
Erasing the ConfigurationRouter#erase startup-config
NOTE: When the router reboots it will be in setup mode
Using Cisco Discovery Protocol (CDP)
A Cisco proprietary protocol Designed to collect information about directly
attached & remote devicesHardware informationProtocol information
Useful in troubleshooting & documenting the network
Getting CDP Timers & Holdtime Information
Configuration CDP Timer: How often CDP packets are transmitted to all
active interfaces CDP Holdtime: The amount of time that the device will hold
packets received from neighbor devicesRouter#sh cdp
Global CDP information
Sending CDP packets every 60 seconds
Sending a holdtime value of 180 seconds
Router#config t
Router(config)#cdp timer 90
Router(config)#cdp holdtime 240
Getting Neighbor Information
Shows information about directly connected devices CDP packets are not passed through a Cisco
switch Can only see what is directly attached
Router#sh cdp neiorRouter#sh cdp neighbor detail
Detailed information; hostname, IP address, etc
Getting Interface Traffic & Port Information
Interface Traffic Information: CDP packets sent & received Errors with CDP
Router#sh cdp traffic
Port & Interface Information: Encapsulation on the line Timer & Holdtime for each interface
Router#sh cdp interface
Using Telnet
A virtual terminal protocol Part of the TCP/IP suite Allows connections to remote devices
Gather informationRun programs
NOTE: The VTY passwords NOTE: The VTY passwords mustmust be set on the routers be set on the routers
Using Telnet
Setting VTY passwords:Router#config t
Router(config)#line vty 0 4
Router(config)#login
Router(config)#password cisco
Router(config)#^Z
Router#172.16.10.2
Trying 172.16.10.2 … Open
User Access Verification
Password:
RouterB>
Using Telnet
Setting VTY password:Router#config t
Router(config)#line vty 0 4
Router(config)#login
Router(config)#password cisco
Router(config)#^Z
Router#172.16.10.2
Trying 172.16.10.2 … Open
User Access Verification
Password:
RouterB>
Remember…. VTY password is the user mode
(>) password - not the enable mode (#) password
With no enable/enable secret password set, the following happens:
RouterB>en
% No password set
RouterB>
This equates to good security!
Telnet Commands
Telnetting into Multiple DevicesCtrl+Shift+6 (release) X
Checking Telnet ConnectionsRouter#sh sessions
Checking Telnet UsersRouter#sh users
Closing Telnet SessionsRouterB>exitRouterB>disconnect
Resolving Hostnames
To use a hostname rather than an IP address to connect to a remote host a device must be able to translate the hostname to an IP address Build a host table on each router Build a Domain Name System (DNS) server
Building a Host Table
Provides name resolution only on the router on which it is built
[ip host name tcp_port_number ip_address]
Router(config)#ip host RouterB 172.16.10.2
Router(config)#ip host switch 192.168.0.148
Router#sh hosts Default TCP port number: 23
Router#RouterB
RouterB#(Ctrl+Shift+6) (X)
Router#switch
Using DNS to Resolve Names
Used when you have many devices on your network
Making DNS work… ip domain-lookup
Turned on by default ip name-server
Sets the IP address of the DNS server (up to 6 ea.) ip domain-name
Appends the domain name to the hostname
Ex: RouterA.neversail.navy.mil
Checking Network Connectivity
Ping Displays the minimum, average, & maximum times it
takes for aping packet to find a spedified system + returnRouter#ping RouterB
Trace Shows the path a packet takes to get to a remote device
Router#trace RouterB
Summary
Backed up a Cisco IOS to a TFTP server Upgraded or restored a Cisco IOS from a TFTP server Backed up and restored a Cisco router configuration using a
TFTP server Used the Cisco Discovery Protocol to gather information
about neighbor devices Created a host table on a router and resolve host names to IP
addresses Verified your IP host table Used the OSI model to test IP