Desigining Cisco Networks
Start Here
If you have not read any of the material and are not ready for this cram session, start here with Cisco's internetworking design documentation.
A good technology overview can be found here on Cisco's website. This goes over all the basic technology that you would need to know for the test.
Internetworking Fundamentals
Cisco’s Fundamentals Online: Click here Cisco’s Internetwork Design Guide: Click here OSI:
OSI LAYER
|
FUNCTIONS
|
APPLICATION
Message/data
|
Service advertisement, service availability. Manages communications between applications. (FPDAM) File, Print, Database, Application, and Messaging services. Allows applications to use the network. Handles network access, flow control and error recovery. |
PRESENTATION Message/data
|
Translation, compression, encryption, data
conversion. Translates data into a form usable by the application layer. The
redirector operates here. Responsible for protocol conversion, translating and
encrypting data, and managing data compression.
|
SESSION
Message/data
RPC (Remote Procedure calls) functions
here.
|
Connection establishment, data transfer,
connection release (Half duplex, full duplex, simplex). Allows applications on
connecting systems to establish a session. Provides synchronization between
communicating computers.
|
TRANSPORT
Segments (or Datagrams)
|
Service addressing, segmentation and
transport control, flow control, end-to-end data integrity. Responsible for
packet handling. Ensures error-free delivery. Repackages messages, divides
messages into smaller packets and controls error handling.
|
NETWORK
Packets (or Datagrams)
|
Logical addressing, switching, routing,
network control. Translates system names into addresses. Determines routes for
sending data and manages network traffic problems, packet switching, routing,
data congestion and reassembling data.
|
DATA LINK
Frames
|
Sends data from network layer to physical
layer. Manages physical layer communications between connecting systems.
LLC Layer (Logical Link Control): flow
control and timing (802.2). Manages link control and defines SAPs (Service
Access Points).
MAC Layer (Media Access Control): framing
and physical addressing (802.3, 802.4, 802.5, 802.12). Communicates with adapter
card.
|
PHYSICAL
Bits
Is concerned with definition of low level
functions (voltage, media types)
|
Transmits data over a physical medium.
Defines cables, cards and physical aspects as well as electrical properties,
transmission media, transmission devices, physical topology, data signaling,
data synchronization and data bandwidth. Manages data placement on and data
removal from the network media.
|
TCPIP Addressing: IP basics Documentation by Cisco
Class A
|
1-127
|
Class B
|
128-191
|
Class C
|
192-223
|
Class D
|
Multicast
|
Class E
|
Experimental
|
Decimal
|
Subnets
|
# Class A Hosts
|
# Class B Hosts
|
# Class C Hosts
|
.192
|
2
|
4,194,302
|
16,382
|
62
|
.224
|
6
|
2,097,150
|
8,190
|
30
|
.240
|
14
|
1,048,574
|
4,094
|
14
|
.248
|
30
|
524,286
|
2,046
|
6
|
.252
|
62
|
262,142
|
1,022
|
2
|
.254
|
126
|
131,070
|
510
|
NA
|
.255
|
254
|
65,534
|
254
|
NA
|
Class A
|
10.0.0.0
|
10.255.255.255
|
Class B
|
172.16.0.0
|
172.31.255.255
|
Class C
|
192.168.0.0
|
192.168.255.255
|
Well-Known Ports
|
0 - 1023
|
Registered Ports
|
1024 – 49151
|
Dynamic or Private Ports
|
49152 – 65535
|
Type
|
Number
|
FTP - Data
|
20
|
FTP - Control
|
21
|
TFTP - UDP
|
69
|
SMTP
|
25
|
POP3
|
110
|
SNMP | Trap - UDP
|
161 | 162
|
DNS - UDP
|
53 (TCP zone
transfer)
|
TELNET
|
23
|
TIME
|
37
|
TACACS
|
49
|
FINGER
|
79
|
HTTP
|
80
|
NNTP
|
119
|
NTP
|
123
|
NETBIOS
|
137-139
|
DHCP Server - UDP
|
67
|
DHCP Client - UDP
|
68
|
RPC - UDP
|
111
|
- Routed Protocols are
IP, IPX and AppleTalk
(AT).
- Routing protocols are OSPF, RIP, RIP II, EIGRP, NLSP, RTMP, etc.
- These are Internal Routing protocols where BGP would be external.
- Distance vector protocols are RIP, RIP II, IGRP, and IPX RIP.
- Link State Protocols are OSPF, NLSP, etc
- EIGRP is considered a Hybrid Routing protocol
- Important routing Protocols based on TCPIP, NOVELL or AppleTalk:
- IP-
RIP
- IP – OSPF
- IP – EIGRP
- IPX – IPX RIP
- IPX – NLSP
- IPX – EIGRP
- AT – RTMP
- AT – EIGRP
- IP – OSPF
- Notice EIGRP (the Hybrid) works with them all
- Scalability restraints
- IP –
500
Workstations
- IPX – 300 Workstation
- AT – 200 Workstations
- NetBios – 200 Workstations
- Mixed - 200 Workstations
- IPX – 300 Workstation
- MTU – You should be careful and avoid changing the size of the Maximum Transmission Unit, but if you do, you can improve network performance by manipulating that size to be the largest possible.
- Ipv4 Header size: 20 Bytes W/Options
- Ipv6 Header size: 40 Bytes Fixed
- Standard administrative distances for IP routes (the lower the number the more preferred the route will be)
- Routing protocols are OSPF, RIP, RIP II, EIGRP, NLSP, RTMP, etc.
Directly connected interface
|
0
|
Static route using connected
interface
|
0
|
Static route using IP
address
|
1
|
EIGRP summary route
|
5
|
External BGP route
|
20
|
Internal EIGRP route
|
90
|
IGRP route
|
100
|
OSPF route
|
110
|
IS-IS route
|
115
|
RIP route
|
120
|
EGP route
|
140
|
External EIGRP route
|
170
|
Internal BGP route
|
200
|
Route of unknown origin
|
255
|
- IP RIP
30
seconds
- IP IGRP 90 seconds
- AppleTalk RTMP 10 seconds
- IPX RIP 60 seconds
- IPX SAP 60 seconds (SAP is not a routing protocol)
- IP IGRP 90 seconds
- Ethernet
segments should not exceed 40% Network Utilization
- Token Ring should not exceed 70% Network Utilization
- WAN Links should not exceed 70% Network Utilization
- Response time should be less than 100ms
- Broadcasts/Multicasts should be no more than 20% of all network traffic
- On Ethernet there should be no more than 1 CRC error per 1million bytes of data
- Cisco Router CPU Utilization should not exceed 75%
- On Ethernet segments, less than .1% of the packets should result in a collision.
- On Token-Ring segments, less than .1% of the packets are soft errors not related to ring insertion.
- On FDDI segments, there should be at most one ring operation per hour not related to ring insertion
- On Cisco routers, the output queue drops should be less than 100 per hour.
- On Cisco routers, the input queue drops should be less than 50 per hour.
- Token Ring should not exceed 70% Network Utilization
- Static Routing –
manually assigned by the Admin user entering the
routes
- Dynamic Routing – generated/determined by a Routing Protocol
- With Dynamic Routing,
routers pass information between each other so that routing tables are regularly
maintained.
- The routers then determine the correct paths packets should take to reach their destinations.
- Information is passed only between routers.
- A routing domain is called an Autonomous System, as it is a portion of the Internetwork under common admin authority.
- Consists of routers that share information over the same protocol. Can be split into routing areas.
- The routers then determine the correct paths packets should take to reach their destinations.
- Used in smaller networks
that are have fewer than 100 routers.
- Easy to configure and use.
- As routers increase in number, you need to consider CPU utilization, convergence time, and bandwidth utilization.
- Convergence is due to routing updates at set intervals; e.g., 90 seconds.
- When a router recognizes a change it updates the routing table and sends the whole table to all of its neighbors.
- Routing loops or counting to infinity occurs because of the delay in sending updates. This problem can be fixed with:
- Split
Horizon - Info cannot be sent back on the interface it was received from
- Route Poisoning - When the network goes down, route gets set to 16 or unreachable until it’s back up
- Hold–Downs - Prevents routes from changing too rapidly in order to determine if a link has really failed, or is back up
- Route Poisoning - When the network goes down, route gets set to 16 or unreachable until it’s back up
- Easy to configure and use.
- Maintains Topology
Database.
- Routers have formal neighbor relationship.
- Exchanges LSA (Link State Advertisement) or hello packets with directly connected interfaces.
- These are exchanged at short intervals (typically 10 sec).
- Only new info is exchanged.
- Scales well: only downside is that link–state protocols are more complex.
- Routers have formal neighbor relationship.
Application
|
AFP
|
Presentation
|
|
Session
|
ADSP, ZIP, ASP, PAP
|
Transport
|
RTMP, AURP, NBP, ATP,
AEP
|
Network
|
DDP, AARP
|
Datalink
|
ELAP, LLAP, TLAP, FLAP
|
Physical
|
Localtalk
|
- RTMP – Routing Table
Maintenance Protocol – a Distance vector protocol that has a default
update timer of 10 seconds. Updates only when changes occur.
- AURP – AT Update-based Routing Protocol that allows the creation of a tunnel to interconnect two AT based networks through TCPIP to form an AT WAN. AURP uses UDP. It does not send periodic updates through the link.
- With AT, your client devices will automatically select a network address and will then broadcast a probe to ensure that it is unique.
- AURP – AT Update-based Routing Protocol that allows the creation of a tunnel to interconnect two AT based networks through TCPIP to form an AT WAN. AURP uses UDP. It does not send periodic updates through the link.
- Enhanced Interior Gateway
Routing Protocol
- A hybrid Routing protocol
- Proprietary to Cisco
- Uses metrics: BAN-DEL-REL-LO-MAX (How I remember it)
- BANDWIDTH
- DELAY
- RELIABILITY
- LOAD
- MTU (Maximum Transmission Unit) Notes on MTU
- DELAY
- A hybrid Routing protocol
WAN and LAN protocols
Ethernet: Cisco documentation on Ethernet, Fast Ethernet and Gigabit. You must know this-
Meters –185
|
Cable -Thinnet
|
|
Meters –500
|
Cable –Thicknet
|
|
Meters –100
|
Cable -UTP
|
|
Meters –100
|
Cable -UTP
|
|
Meters –400
|
Cable -Fiber
|
|
Meters –100
|
Cable -UTP
|
|
Varies
|
Varies
|
- Asynchronous Transfer
Mode
- FIXED length, 53 byte cells (48 payload +5 header).
- ATM Layers are at layer 2 while the Adaptation Layer is Layer 3.
- AAL’s have the responsibility of isolating the upper layer protocols from the ATM process details.
- Frame types (or better to be called Adaptation layers)
- AAL1 –
will take a continuous bit stream and will place it within the ATM cells, between
source and destination – ATM will Require timing synchronization.
- AAL3/4 – supports connectionless and connection-oriented data. Adds a header and a trailer whereas AAL5 does not. (Messages can be interleaved)
- AAL5 – Also supports connectionless and connection-oriented data but also supports LANE. (LAN Emulation) AAL5 can also be referred to as SEAL (Simple and Efficient adaptation layer)
- AAL3/4 – supports connectionless and connection-oriented data. Adds a header and a trailer whereas AAL5 does not. (Messages can be interleaved)
- A knowledge of ATM and its framing should be reviewed.
- FIXED length, 53 byte cells (48 payload +5 header).
- Point to point
protocol.
- Major benefit is the use of more protocols then just TCPIP.
- There are other protocols used
- LCP
– Will establish, then configure (and test) the connection
- NCP – (A family of NCP’s) will establish and configure the upper layer protocols.
- PPP uses HDLC as a basis to have encapsulation of Datagrams over Point-to-point links.
- HCLC –High level data link control.
- Make sure you are comfortable with the whole PPP process.
- Major benefit is the use of more protocols then just TCPIP.
- A WAN protocol that
operates at Layers 1-3 of the
OSI
- Offers Error checking but becomes slower due to that extra checking
- X.25 Protocol suite
- Layer 3
– PLP (Packet Layer Protocol) will manage the packet exchange
between the DTE devices across a virtual
link
- Layer 2 – LAPB (Link Access Procedure B) Data Link Layer Protocol that will deal with the packet framing between the DTE and DCE devices. Operates at Layer 2. Integrated into X25. Router can be DTE or DCE. HDLC confined to ABM transmission. Job is to make sure that frames are error free. There are three different frame types: Information frames - flow control, error detection; S Frames - requesting and suspending communications; and U Frames - link setup, disconnecting, error reporting. Has high overhead, but good error checking
- Layer 1 – (X.21bis) X-21bis will handle the Layer 1 aspects of activation / deactivation at speeds of up to 19.2 Kbps.
- Layer 2 – LAPB (Link Access Procedure B) Data Link Layer Protocol that will deal with the packet framing between the DTE and DCE devices. Operates at Layer 2. Integrated into X25. Router can be DTE or DCE. HDLC confined to ABM transmission. Job is to make sure that frames are error free. There are three different frame types: Information frames - flow control, error detection; S Frames - requesting and suspending communications; and U Frames - link setup, disconnecting, error reporting. Has high overhead, but good error checking
- X.25 uses other physical layer serial interfaces: EIA-TIA 232, EIA-TIA 449, EIA-530 and G.703.
- Offers Error checking but becomes slower due to that extra checking
- Main SNA link layer protocol. PTP, half, full duplex. Two node types: Primary Stations control other stations, setup and manage links. Secondary stations can only transmit to the primary and only after permission.
- Link layer protocol for Serial links. Cisco Default. Supports the following modes: Normal Response Mode – as per Secondary under SDLC; Asynchronous Response Mode allows secondary to communicate without permission; Asynchronous Balanced mode combines the two stations. Has lower overhead than LAPB but less error checking.
- E = Existing
network
- Q = Switching and signaling
- I = Concepts, terminology and service
- Q = Switching and signaling
- Establishes a Frame relay
Virtual Circuit that is a connection between two DTE devices.
- Two circuit types: Permanent (PVC) and switched (SVC) identified by DLCI.
- Multi–protocol support: IP, DECnet, Appletalk, IPX, XNS, ISO.
- More efficient and faster than X.25 because of less error checking.
- Default encapsulation on CISCO is CISCO or can be IETF. Use IETF if connecting to non–Cisco devices with frame relay.
- DLCI – Data Link Connection Identifier – IP addresses need to be mapped to DLCI's to communicate over a virtual circuit. Can be done dynamically with IARP or manually though the map command.
- LMI - Local Management Interface – gives DLCI global rather than local significance. Makes entire frame relay network appear as typical LAN. Manages status-providing info on keep–alives, multicasting, addressing and status of virtual circuit. With version 11.2 of IOS, auto–sensed.
- Three LMI types Cisco (default) ANSI and q933a.
- Subinterfaces allow you to route IP on one virtual circuit and IPX on the other.
- Some routers have limits - 2500 can handle max of 255. Two types of sub interface Point–to–point and multipoint.
- Two circuit types: Permanent (PVC) and switched (SVC) identified by DLCI.
- DE – Discard
Eligibility used to identify traffic importance
- FECN (Forward Explicit Congestion Notification) – To tell others the path is congested
- BECN (Backward Explicit Congestion Notification) – Goes back to sending router to tell it to slow down
- CIR (Committed Information Rate) – Minimum bandwidth guaranteed. Choose realistic level; can choose zero if retransmission is acceptable. Can be by BC or committed burst size that allows customers to exceed CIR for limited time
- FECN (Forward Explicit Congestion Notification) – To tell others the path is congested
- Bridging basics: Creates
a single data–link, flat network
- Transparent
Bridging – Connects two or more Ethernet segments. Learns MAC address of
all devices and then starts filtering.
- Integrated Routing/Bridging – Allows you to route and bridge the same protocol by using a virtual bridge–group interface
- Source–Route Bridging – Knows the entire route to destination before it sends data. Not designed for large networks.
- Source–Route Transparent Bridging – Use this when you have to go across bridging domains. Affects spanning tree, as packets cannot cross over domains and therefore you cannot have multiple paths between these domains.
- Integrated Routing/Bridging – Allows you to route and bridge the same protocol by using a virtual bridge–group interface
- Source Route Bridge (also known as –SRB)
- Route descriptors – They are bridge/ ring #’s fields in a RIF. They are used to set the path that a frame should take on a SRB network.
- SRB frames contain a RIF that has routing descriptors to the destination
- SRB networks use DLSw+ to establish a TCP link so that it can reduce NetBios / broadcast traffic queries occurring between peers.
- In SRB networking, the SOURCE determines the route to arrive at the destination node BEFORE sending information frames to it.
- In SRB networking, the source node will acquire the routes to destinations using something called EXLORER FRAMES.
- SRB can use STP, but does not rely on it because it is usually loop free. It would use STP when sending explorer frames to reduce the traffic on the line during its route discovery process.
- SRB is locked down to a hop count of 7 bridges.
- Transparent
Bridging – Connects two or more Ethernet segments. Learns MAC address of
all devices and then starts filtering.
Router Basics
Router Switching:- Process
Switching
- Packet gets copied to process buffer, address is retrieved and the packet is encapsulated and forwarded on the appropriate outbound interface. Cache is updated and subsequent packets to the same address are handled on cached info. Most processor intensive.
- Silicon Switching
- Only 7000 Series + SSP6. The SSP is a dedicated switch processor that takes over from the router processor. Fast solution.
- Optimum Switching
- Faster than both Fast and Netflow Switching. Replaces fast switching on high-end routers.
- Fast Switching
- Is used when no entries exist in more efficient caches; on by default in low-end routers; sometimes necessary to disable due to memory limits or to aid troubleshooting.
- Autonomous Switching
- Compares packets against autonomous switching cache. When a packet arrives the interface checks the switching cache closest to it. Only found on 7000 and AGS+ series routers.
- Distributed Switching
- Happens on VIP (Versatile Interface Processor), very efficient. Gets more efficient as more VIP cards added. No need to use router processor.
- Netflow Switching
- Admin tool increases overhead; gathers stat data, port, protocol, and user info that can be sent to a management station.
- Show
interface - Will show router Layer 2 errors (CRC, collisions, etc.)
- Ping | traceroute - Enables you to ping and perform Route Tracing functions
- Show access-lists - Will display your access lists and you can also specify by number
- Debug - Shows real time - should be used with caution - very CPU intensive
- Show {protocol} route - Will show routing table
- Show processes - Will show CPU usage and CPU time
- Show buffers - Will show usage and misses
- Ping | traceroute - Enables you to ping and perform Route Tracing functions
- Contiguous networks are
grouped together and advertised as a single entity called a supernet.
- Move network prefix to the left (i.e., borrow bits from network portion of address) to describe a single route to contiguous block of IP addresses (Classless Inter–Domain Routing or CIDR).
- This can only be done using contiguous IP addresses.
- Move network prefix to the left (i.e., borrow bits from network portion of address) to describe a single route to contiguous block of IP addresses (Classless Inter–Domain Routing or CIDR).
- IOS Software:
Familiarize yourself with IOS feature sets:
Click here
- Offers a rich set of features:
- Access lists
– to filter /
security
- Proxy services – see below
- Encryption - never use if CPU is at 65% utilization
- Compression – to compress / WAN-serial link optimization
- Queuing – FIFO, Weighted fair, Priority, custom
- Proxy services – see below
- Proxy services:
- IPX GNS
Request
- IPX Watchdog Spoofing
- Proxy ARP
- IP Helper
- IPX Watchdog Spoofing
- Offers a rich set of features:
Design Fundamentals
Hierarchical Topologies (Cisco defines a three–layered approach)
CORE
|
|
DISTRIBUTION |
|
ACCESS |
|
Cisco's Small/medium Sized Business Solution Framework
Broken into three Categories:
Media Problems
-USE A SWITCH
|
|
Protocol
Problems -USE A
ROUTER
|
|
Transport
Problems -USE ATM OR fast /
Gigabit Ethernet
|
|
Analyzing Customer Requirements falls into two areas:
Administrative Data
|
|
Technical Data |
|
Network Management: (FCAPS)
F
|
Fault Management
|
C
|
Configuration Management
|
A
|
Accounting Management
|
P
|
Performance Management
|
S
|
Security Management
|
Business / Political
Constraints
|
|
Technical assessment - constraints |
|
Twelve steps to document the customers existing network:
1. Characterize the Customer’s
applications
|
|
2. Characterize the network protocols |
|
3. Document the current network |
|
4. Identify the potential bottlenecks |
|
5. Identify the business constraints / inputs into the network design |
|
6. Characterize the existing network availability |
|
7. Characterize the network performance |
|
8. Characterize the existing network reliability |
|
9. Characterize the network utilization |
|
10. Characterize the status of your major routers |
|
11. Characterize the existing network management tools |
|
12. Summarize the health of the existing network |
|
Fields for documenting the customer’s existing applications: (Step 1)
Application
|
Application type
|
# Of users
|
# Of hosts or servers
|
Segment
|
Comments
|
Identify each application Running on
the network
|
Characterize the type of
application
Database, Web
|
# Of users for each
application
|
How many servers provide each of the
applications
|
The segments the application runs
on
|
Comments that could be useful at a
later time
|
Protocol
|
Protocol type
|
# Of users
|
# Of hosts or servers
|
Comments
|
Identify each Protocol Running on the
network
|
Characterize the type of Protocol
– routing, routed, LAN
|
# Of users for each
Protocol
|
How many use each of the
Protocols
|
Comments that could be useful at a
later time
|
A network map should include the following:
- The type and speed of each major segment or link
- The names and addresses of major internetworking devices and servers
Your client may already have one so start there and fill in any missing information.
In addition to a network map, you should also notate any addressing scheme that exists in the network.
Three Part Firewall:
External:
|
DMZ (De-Militarized Zone): (Isolation
LAN)
|
Internal:
|
On the outside of the isolation LAN is
a router that will implement access lists to filter traffic usually from the
Internet.
|
|
An internal filtering router permits access to the internal LAN from the isolation LAN or to filter it. |
Note: A PIX Firewall is Cisco’s Firewall based product, but remember that the IOS has a Firewall / NAT based feature set.
Design Document Components: Responding to an RFP (Request for Proposal)
Executive Summary
|
|
Design Requirements |
|
Design Solution |
|
Summary |
|
Appendixes |
|
Cost (Optional) |
|
Network Management:
Cisco documentation on SNMP and RMON
Managed device
|
Is a router or switch with agent
software.
|
NMS
|
Runs network management applications.
Polls devices for SNMP information and configuration.
|
Agent
|
Gather statistics.
|
|
|
CiscoWorks Blue |
|
CiscoWorks2000 |
|
CiscoView |
|
Cisco ConfigMaker |
|
Netsys Baseliner |
|
RMON |
|
Traffic Director |
|
For a detailed list of most of Cisco’s Network Management tools: Click here
Routers and Switches:- Make yourself familiar with the Product
lines:
Click here
- Click here for a Switches index: click here
- Core High-end routers: Click here
- Routers: Click here | Switches: Click here
- Click here for a Switches index: click here
- Pilot –
Very small implementation, used to get your point
across
- Prototype – A larger scale and costly test of your design.
- Make sure you have studied
thoroughly; you will be asked in depth questions from every corner of your study
guides.
- Make sure you have enough practice with case studies. This is not a test for you to just memorize all these facts. You need to know how to implement them. Therefore, practice the case studies. Click here
- Make sure you are comfortable with the Cisco Product line. You will be expected (like any good designer) too offer your advice on what products to implement for the best price.
- Use the Cisco Site – you can look at most of your information right from the Documentation provided to you. Click here
- Make sure you have enough practice with case studies. This is not a test for you to just memorize all these facts. You need to know how to implement them. Therefore, practice the case studies. Click here