ICND 2 Flashcard: Frame Relay

Frame Relay allows the expansion of the WAN with less hardware by providing virtual circuits; less costly than running multiple leased lines like HDLC and PPP.

For example Router 1 (DTE) at your company site has to connect to Router 2 (DTE) at the other site. In between is the Frame Relay cloud. The Router 1 connects to one switch (DCE) in the cloud, and the other Router 2 connects to anothr swtich (DCE). Router 1 could also connect to a Router 3 and so on.

One router is an access linl which can support multiple virtual circuits to send data to multiple remote routers. Each link is a virtual circuit. The data link header and trailers on each frame. The header holds ad address filed called a DLCI.
DLCI - Data Link Connection Identifier

The notes for this section are taken from the first CCNA Bootcamp course I studied in 2003 by Marketbridge Technologies in Hull-Gatineau. http://www.marketbridge.com/#  The company has grown and changed alot over the years from offering courses to consulting services, but the owner remains the same so it's probably the same company.

Two Frame Relay encapsulations: Cisco and IETF
Cisco is the default, and it means that you have a Cisco router on each end of the Frame Relay network. If you don’t have a Cisco router on the remote end of your Frame Relay network, then you need IETF encapsulation.

Frame Relay is a cost efficicient technology, for intermittent connection from LAN or between endpoints to major backbones or a public WAN.  A permanent virtual circuit (PVC) is formed, enabling the customer to perceive a continous, dedicated connection without having to pay for a full-time leased line; the ISP determines the route each frame travels to its destination and can charge based on usage.  Think of it as shared bandwidth, a portion of the dedicated paid bandwidth to allotted to each user; allows the user to exceed the guaranteed bandwidth if resources are available

However for a truly private network, Frame Relay would run over leased lines over T-1 lines. A dedicated connection during the transmission period is required, but without a steady flow of transmisions, so it is not often used for voice or video.  The data units are in frames in variable sizes.

Packet based switching.
Frame relay is based on the older X.25 packet-switching technology which was designed for analog voice. Frame relay today is fast packet switching because it operates in the Layer 2 data-link layer and not so much Layer 3 network even though a frame can carry packets of Ethernet and X.25 Error checking or resending is up to to the endpoints to evaluate.

DLCI - Data Link Connection Identifier

I really like the description of a frame-relay map and how it joins an DLCI with an IP address much like ARP mapping MAC address to IP. See the IP-to-DLCI mappings with the command, show frame-relay map (IARP is default on Cisco routers).

Possible network topologies
Hub and Spoke: one hub many spokes used with sub interfaces
Partial Mesh or Hub and Spoke - routers do not have a VC to all other routers

Full Mesh: each router has a logical circuit to every other router

Hybrid: Two remote routers may have VC to each other providing full mesh connectivity between them and the hub. The other remote routers may have only one VC back to the hub.
Frame-Relay LMI
Frame-Relay used the Local Management Interface (LMI) protocol to generate keepalives and obtain a status on the virtual circuits.  LMI message formats: Cisco (DLCI 1023), ANSI or Annex D (DLCI 0), and Q.933A or Annex A (DLCI 0?) containing info regarding -

• Keepalives
• Multicasting - Multicasting uses the reserved DLCIs from 1019 through 1022.
• Global addressing - This provides global significance to DLCIs, like a LAN
• Status of virtual circuits - This provides DLCI status.

Possible states for the circuits
Active - the circuit is up and running
Inactive - possible cause, circuit to CO (frame switch) is find but remote end is down
Deleted - circuit to CO not working, interface down or cabling issue, no LMI

Congestion Control in Frame-Relay
DE - Discard Eligibility, mark for packets exceeding the CIR
BECN - Backward Explicit Congestion Notification, tell source to slow down transmission
FECN - Forward Explicit Congestion Notification, tell destination there was congestion in the cloud
An excellent summary of everything you need to know about Frame Relay for Cisco CCNA, written like a study blog with network diagrams. The style of writing is like an instructor speaking. Click here.

usage: conf t
encapsulation frame-relay

Scenario
There are seven remote sites to connect and only one serial port on the router. Instead of seven leased lines, frame-relay might be a good soluction to statistically multiplex multiple logical circuits over one physical interface to save money.

Access rate The maximum speed that the Frame Relay serial interface can transmit.

CIR The maximum bandwidth of data guaranteed to be delivered. In reality, it’s the average amount that the service provider will allow you to transmit.

For example if the T1 is carrying an access rate of T1 (1.544Mbps) and you're paying for a CIR of 256Kbps. The first 256Kbps of traffic you send is guaranteed delivery. Beyond that, it's a “burst”— a transmission that exceeds the guaranteed 256Kbps rate and up to the T1 access rate (if that amount is in your contract). I believe this sounds like the whole discussion about paying for bandwidth usage and doing away with unlimited with the CRTC ruling??

Obviously if the combined committed burst (the CIR) and excess burst sizes, known as the MBR or maximum burst rate when combined, exceed the access rate, then the packets will be dropped, depending on the service provider.

Wiring Diagram Quiz

Image Source


Quiz
Assign a type of equipment for each of the points in the network, switch, router etc
Assign a media to each link based on distance- copper, fibre, T1 etc
Post your answers in the comments and let's discuss it!

My colleague had mentioned that MPLS was in alot of the questions in the CCNA Security exam as well as Cisco SDM though he was more familiar with the CLI. I just grabbed this image from google because it has alot of components of a network carrying data, voice, media during my search for MPLS, wire speed!.

Cisco ICND1 Flashcard: Are you tech savvy about DSL, the Last Mile, NAT and PAT?

The topic of DSL was covered in the CCNA Bootcamp course as a requirement for the ICND1 Exam.

Internet Resellers
TekSavvy talk has been making the rounds lately on forums at work and online. They're in the news among the other victims of the ongoing CRTC ruling on the "usage based billing" or wholesale billing regulations from large ISPs to small ISPs. I decided to take a look at what folks were talking about - really cheap rates for high speed internet, long distance calling, residential phone and even cable at much lower rates than the standard Bell or Rogers! However the ruling will make unlimited packages impossible or too expensive, as the cost of using Bell or Internet backbone services is transferred to the consumer, say for example Bell will charge TekSavvy or Acanac an extra $22/ Mbit or 22k for 1 Gbps link. The other thing is I didn't quite understand right away, why when the TekSavvy customers had a problem and they called up TekSavvy tech support, a service call would be sent out to Bell or Rogers. Ok I get it, Bell or Rogers still provide the DSL or last mile connection. TekSavvy is an "internet reseller" or ISP.

There is a business arguement for open competition that folks are feeling very strongly about for Open Media debate and a petition. My article is purely about the electrons not the politics.  Back to the basics.

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What is DSL and the Last Mile?
The story begins with the telephone cabling we are already familiar with. It's copper and can carry 300 Hz to 1 MHz of data. However the human voice is only using the 300Hz to 3 kHz portion of the link, DSL can use the remainder 3 kHz to 1 MHz for high speed data, "always on".  DSL stands for Digital Subscriber Line, and this allows the packets to be sent over copper, owned by an ISP. It is not a shared medium, each user has his own direct connection to the DSLAM. It's scalable, adding new users does not impede the network performance. DSL can be used simultaneously as voice.

The cabling part there is also refered to as the local-loop or last-mile or the last step of the local telephone network connection. DSL may be added incrementally in any area with some distance limitations, but is not universally available everywhere in all geographic locations. Equipment required includes the CPE (Customer Premise Equipment) and DSL-Access Multiplexer (Time Division Multiplexer).  There is a physical geographic limitation of 5.5km distance for ASDL, and some folks would consider the "always on" aspect of the DLS as hackable; well whatever.


DSL can be used by a large company to support the "work at home" workers. The worker cannot connect to the enterprise network directly; instead he first connects to the ISP and then an IP connection is made from the Internet to the enterprise network.

There are two categories of DSL
DSL places the data upload and download above the 4kHz window, allowing voice and data transmission to occur simulataneously on the same DSL service.

ADSL Asychronous, higher download bandwidth than upload (less than 5.5 km distance)
VDSL, VDSL 2 is very high data rate
250 Mbps at the source
100 Mbps at 0.5km
500 Mbps at 1km
G Lite, G 992.2
ADSL, ADSL2, ADSL 2+
Consumer DSL aka G.Lite or G992.2

SDSL Synchronous, same capacity both directions
HDSL high data rate DSL
ISDN DSL(IDSL)
G.shdsl, symmetric high bit data rate DSL

In all instances, it's WAN access. It is not cable; cable is best described as a bus network topology, fiber under the street, copper to the home. (Why do I have this in my notes?)

Transceiver - connects the computer of the worker to the DSL, usually a modem with USB or Ethernet cable. Newer DSL transceiver can be installed on routers with 10/100 switch ports for home and office use.

DSLAM - located at Central Office of the carrier. DSLAM combines individual DSL connections into one high capacity link to the ISP and Internet.

Assigning an IP Address
Used to be that when you turned on your computer the ISP would assign an IP address to your computer by DHCP, and then when you were finished with your connection the computer would return the IP address to the pool. The only thing is, people don't usually turn off the computer so this IP address will almost permanently taken. I suppose if it was a work computer, the network administrator could use Private and Public IP addresses translation.

The global internet  is like a large WAN.  Servers need an IP address from  the ISP and interfaces - which are manualy assigned by the ISP or dynamically assigned.  When you have private IP address and need to go on line. The IP addresses will have to be translated by NAT from an Internal  lab to the outside world.

Next Topic:
NAT, PAT and Overloading

Cisco ICND1 Flashcard: WAN Protocols and Serial Encapsulation, PPP, HDLC

The Usual Scenario that describes most WANs
Use serial point to point connection to connect the LAN to service provider WAN
Have serial point to point connections within the LAN
Use Circuit Switching technology (ICND1 Topic)

ICND2: Packet Switching in Frame Relay and ATM

The Telco provides clocking info for CSUé DSU. The DCE provides clocking, set the clock rate command here, while the receiving device say the customer`s router is a DTE.

What is a T1
T1: 24 DSO's each 64 k
1 DSO is the bandwidth is required for an uncompressed, digitized phone call
a point to point leased line bandwidth specified by a DS number (DS0, DS1 etc)

T1: 1.544Mbps, 24 DSO`s 64 kbps each, 8 kbps overhead
E1: 2.048 MBps, 32 DSO 64 kbps channels

Circuit Switching
A dedicated path is established, maintained, terminated through a carrier network for each session.
Therefore circuit switching creates a dedicated physical connection running PPP, HDLC on Layer 2. Most likely this will be a leased line at fixed capacity, dedicated for the WAN connection.  The Point to Point serial line to form a preestablished WAN communications path

HOW TO Configure a Serial Interface
The serial interface will connect WAN to routers at a remote site

conf t
interface serial 0/0/0
bandwidth 64
clock rate 64000
encapsulation hdlc
no shutdown

Notes: by default Cisco devices are DTE devices but may be configured as DCE
bandwidth: metric used by IGRP routing protocol
clockrate: set clockrate on DCE interfaces in bps, possible 1200, 2400, 4800, 9600, 19200, 38400, 56000, 64000, 72000, 125000 to name a few and 4000000

To configure the clock rate for the hardware connections on serial interfaces, use the clock rate interface configuration command. Use the no form to remove the clock rate if you change the interface from a DCE to a DTE device. Using the no form of this command on a DCE interface sets the clock rate to the hardware-dependent default value.

clock rate bpsno clock rate

The default value could be no clock rate configured, or on a serial interface card I plugged in, it was 2000000 bps.

Clock rate vs Bandwidth
My summary taken from cisco discussion pages on this subject.

Take the example of simple serial PPP linke: on the DCE side of the circuit (that would be the internal part connecting to the CPE of the Service Provider) put "clock rate 64000".  Depending on the IOS version, on the DTE side, you may be able to see this with "show controllers (intf) | include clock" ; reveals the actual tx/rx clock.  The clock rate is required to match the clocks on the receiver and transmitter on remote and local router.the two routers need to sync up their clocks in order to decode the packets coming on their interfaces

Then on the DTE side, look at "show interface (intf) | include BW" and the regular serial link is showing 1544K even though it's only physically possible to send 64K. By default, the routers do not have any mechanism to detect the actual bandwith of a serial line and its is set to a default value of 1.544 MBPs. If there is one 64K serial line and another T1 line on the same router, if the bandwidth value on the 64K serial line is not changed, the router will treat both as T1 lines. Its a method to tell the router that it is a slower link so that actual metrics can be computed accurately.

This bandwidth command tells IOS how to perceive the speed of any particular interface in order to manipulate routing metrics (EIGRP, OSPF); note that the bandwidth command doesn't physically change the speed of an interface like the clock rate command does.

Other commands
show controller serial 1/0, displays information about the physical interface, including clock rate
show interface

HDLC - High Level Data Link Control protocol
HDLC is one of two major data-link protocols, the encapsulation method for data on synchronous serial data links. Error checking built in, enables flow control and error checking using ack, control characters, checksum. However HDLC is not compatible between different vendors. Remember, it uses a frame delimiter to mark the start/ end of each frame

HDLC has a type field that may not be compatible with equipment from other vendors.

Cisco HDLC
Cisco HDLC is a datalink protocol for point to point WAN connections. It is the default encapsulation for serial lines. There is no windowing no flow control, only point to point. Some extensions allow multiprotocol support before ppp was specified
* will not interoperate with other HDLC implementations
* use PPP when interoperability is required, for example if two Nortel and Cisco devices were connecting

ISDN
Different ISDN services - voice and data can run over existing telephone lines. The BRI (basic rate interface) uses two B channels (64 kbps each, may be combined) and one D channel (16 kbps). B for bearer for voice and data; D for data for call signalling or clocking.

An ISDN interface can run these protocols:
E protocols for ISDN on existing telephone network.
I protocols for concepts, terminology and services.
Q protocols refer to switching and signaling.

A Service Provider may use Signaling System 7 (SS7) between the two switches—the same protocol used inside phone company networks to set up circuits for phone calls.  ISDN PRI in North America is like a digital T1 circuit

ISDN BRI and PRI Reference Point Diagrams

PPP
Point to Point protocol is a data-link protocol, provides router to router and host to network connections over both synchronous and asynchronous circuits. So, it transports Layer 3 packets across the data-link layer. PPP can be applied to these physical interfaces:
1) asynchronous connection - think of a dial up connection
2) synchronous connection - think of a leased line, like ISDN media
3) High Speed Serial Interface HSSI

What features not available in HDLC but found in PPP:
1) link quality management feature to monitor quality of link. Too many errors detected, ppp takes down the link
2) supports Password Authentication Protocol PAP and CHAP (three way hash authentication)

Three phases of PPP
The method for encapsulating multiprotocol datagrams
* Link establishment phase- LCP extensible link control protocol, establish, configure, test the WAN link
* authentication phase of ppp is optional (choose PAP or CHAP)
* Network Layer protocol phase - NCP network control protocol, to establish and configure different network layer protocols, example IPCP, Appletalk Control Protocol, Novell IPX Control Protocol, Cisco Systems CP, Systems Network Architecture (SNA) CP, Compression CP

Main components:
E1A/ T1A 232C - connector, physical layer standard for serial comms
HDLC - high level data link control, for encapsulating datagrams over serial links
LCP negotiates traffic, maintaining or terminating traffic
NCP encapsulates traffic, multiple network layer protocols.

LCP configuration options
Authentication - identifying the sender, PAP or CHAP
Compression - Cisco uses Stacker and Predictor compression methods
Error Detection - Quality and Magic Numbers
Multilink - splits the load over two or more parallel circuits, or a bundle

PAP
- Password Authentication Protocol; passwords are sent in the cleartext, PAP is only for the initial link establishment

CHAP
- Challenge Authentication Protocol; used at the initial startup of the link and at periodic checkup times to make sure the router is still communicating with the same host. Router sends challenge request to the remote device, expects a value calculated by the one way hash function MD5. If the values don't match, the link is terminated.

Configuring PPP and authentication
* hostname RouterX, assign a hostname to RouterX
* username RouterY password B007! , identify the username RouterY and password of remote router
* conf t, then go to the serial interface in question
* encapsulation ppp, enable ppp encapsulation
* ppp authentication chap, enable chap authentication or use pap instead

Sample configuration
conf t
int s0
encapsulation ppp

Conf t
hostname routerX
username routerY privilege 15 secret 0 password B007!!
encapsulation ppp
ppp authentication chap
(or ppp authentication pap)

debug ppp authentication
Verify
show interfaces
show interface serial
show interface s0

Cisco ICND1 Flashcard: WAN Hardware and Encapsulation

ICND1: PPP
ICND2: Frame Relay

Wide Area Networks

A LAN will cover an area in the same building or vicinity; a WAN spans a much larger geographically connected sites. Setting up and maintain a WAN is very expensive, most private companies would rather purchase a WAN connection from the ISP, who will manage the WAN infrastructure and back-end network backbone.  Services include T1, T3, E1 and E3, DSL, cable, frame-relay and ATM.

WAN operations cover the Layer 2 Data Link Layer (Metro Ethernet, MPLS, frame-relay, ATM, HDLC)and Layer 1 Physical Layer components (electrical, mechanical, operational connections).


WAN Devices
Equipment required includes a modem CSU/DSU to connect to the service provider, and edge devices modify the Ethernet encapsulation to the serial WAN

Wan Ecapsulation Answer Hack. Is this legal?

Modem - modulates an analog carrier signal to encode the digital signal, and modulates the carrier signal to decode the transmitted information.

CSU/ DSU - Channel Service Unit/ Data Service Unit. CSU is termination for the digital signal ensures integrity, error correction, and line monitoring. DSU converts T Carrier line frames into LAN frames. Provides a clocking signal to the customer equipment interface from the DSU, terminate the channelized transport media of the carrier on the CSU. CSU also provides a loopback test diagnostic.

Demarcation Point, the point where a service provider considers the services delivered, such as the CSU/DSU on customer's premises to the provider's Central Office.
Access Server - I'll check my notes what that is for.

WAN Switch - used in carrier networks to carry Frame Relay, ATM, X.25 and PSTN in the cloud

Router - The router can be a WAN connection device, with serial interface ports to connect to the  service provider and the internetwork for the LAN. Basically a router will connect to the POP router of the ISP

Core Router -  needs explaining

CPE - Customer Premise Equipment that includes a DCE/ DTE.
DCE - Data Circuit-terminating Equipment or Data Communications Equipment, the device that ports data on the local loop.Configure the clock rate for the DCE interface.
DTE - Data Terminal Equipment, customer equipment that passes data to the DCE such as the routers. Synchronizes to the clock rate.

There is a lengthy description of EIA/ TIA connectors, but the most important part is the router end of the shielded serial transition cable which has a DB-60 connector. The DB-60 port on a serial WAN interface car is a 5 in 1 port. There is a new type of cable called a Smart Serial Cable.

Summary of WAN Links Hierarchy
Three main WAN types: Dedicated, Circuit Switched and Packet Switched.

DEDICATED
Leased Lines: T1/ E1
For companies who constantly send traffic, expensive.
SWITCHED
Circuit Switched: PSTN, ISDN, analog modem
For companies who send occassional traffic, least expensive.

Packet Switched: Frame Relay, x.25
Ideal for companies requiring a minimum constant service without the cost of dedicated lines.

Cell Switched: ATM
INTERNET
Broadband:VPN
Other: DSL Cable, Broadband, Wireless

The Last Mile
This refers to the local loop, the last mile connection that defines how the local user gets to the ISP perhaps? One example is for example, installing a new fiber optic cable from the exchange outside the building into the networking lab perhaps. Another example could be a satellite hop.

Long Range Connectivity
The protocols SONET and Synchronous Digital Hierarchy (SDH) have been around for ages. These are used to move large amounts of data over great distances through fiber optic cables, mostly refering to voice and data.  A newer optical technology, Dense Wavelength Division Multiplex (DWDM) provides extremely long range communications by assigning a specific frequency (or wavelength) of light to incoming signals.  Equipment can amplify  the wavelength to boost  signal strength. A single DWDM fiber can have more than 80 different wavelengths or channels multiplexed, each channel carrying up to 10 Gb/s.  The other important feature is that DWDM can carry IP, SONET, ATM at the same time on the same optical fiber.

At the receiving end, the router needs the right optical SFP.

Related Topics: PPP Encapsulation, ISDN
Next Topic: DSL two types-ADSL and SDSL
Followed by: Cisco IPSec VPN