BrainBuzz
Cramsession

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Contents
Contents .............................. 1

Cisco Device Operation........... 2

General Networking Theory .... 5

Internetwork Expert

Abstract:

This Cramsession will help you to
prepare for Cisco exam #350-001, the
CCIE written exam. Exam topics include,
Cisco Device Operation, General
Networking Theory, Bridging & LAN
Switching, Internet Protocol, IP Routing
Protocols, Desktop Protocols,
Performance Management, WAN, LAN,
Security, and Multiservice.
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2



The EXEC commands that will show hardware configuration of a Cisco router are
“show hardware” and “show version”
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Mode Prompts
Monitor mode rommon 1 >
User mode router>
Privileged mode router#
Global configuration mode router(config)#
Interface configuration mode router(config-if)#
Sub-interface configuration mode router(config-subif)#
Line configuration mode router(config-line)#
Router configuration mode router(config-router)#
IPX router configuration mode router(config-ipx-router)#

Really Delete Files from Flash

When you delete a file from flash, it is not removed from flash, and you will not

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Types of passwords:
• Exec – used to restrict access to the EXEC mode, the basic console on the
router.
• Enable – used to restrict access to the privileged EXEC mode where changes
to the router configuration can be made.
• Enable Secret – Similar to the Enable password, but they are encrypted so
they cannot be read.

Setting different types of passwords:
• Console password – used with the routers console port.
router(config)# line con 0
router(config-line)# login
router(config-line)# password {password}
• Auxiliary password - used for the router’s auxiliary port.
router(config)# line aux 0
router(config-line)# login
router(config-line)# password {password}

• Virtual terminal password – used for telnet sessions to router.
router(config)# line vty 0 4
router(config-line)# login
router(config-line)# password {password}
• Enable password – used when enable secret is not configured or software
revision is too old.
router(config)# enable password {password}

• Enable secret password – encrypted password that provides enable privileges.

To enable SNMP on a router the command is "snmp-server community"

General Networking Theory
OSI Model
The OSI is a common tool for conceptualizing how network traffic is handled. In the
CCIE track, we will be interested primarily in the lower three levels. Just a reminder,
that you can use the old mnemonic “All People Seem To Need Data Processing” as a
way to help remember the sequence.

7. Application – User interface tools (such as Telnet, SMTP, FTP, etc.)
6. Presentation – Encoding/Decoding (such as ASCII, MPEG, GIF, JPEG, etc.)
5. Session – Creating, managing and terminating Presentation layer
4. Transport – Error checking and recovery, flow control and multiplexing (TCP,
SPX, etc.)
3. Network – Routing (IP, IPX, etc.)
2. Data Link (LLC/MAC)
• LLC – Manages communications
• MAC – Manages addressing and access to the physical layer
1. Physical – Establish and maintain physical connectivity

Cisco Hierarchical Internetworking Model
• Core – Concentrates all traffic traversing the network. The focus in on speed
and fast switching. Gigabit Ethernet and ATM are seen here.
• Distribution – Control layer; Aggregation of traffic, access lists, compression,
encryption and other services that provide the glue between Access and Core
layers.
• Access – The point at which users join the network. VLANs, WAN
connections, RAS services are all at this layer.

Connection-oriented vs. Connectionless Service

• TCP and LLC Type 2 are reliable protocols because they are layer four
protocols
• IP, UDP, and Frame Relay are NOT reliable protocols because they are layer
three protocols

802.x Protocols
802.2 Link Layer Control (LLC)
802.3 CSMA/CD Access Method (Ethernet)
802.4 Token Ring Bus
802.5 Token Ring
802.6 MAN (Metropolitan Area Network)
802.7 Broadband
802.8 Fiber-optic LANs
802.9 Integrated Voice & Data
802.10 LAN/MAN Security
802.11 Wireless
802.12 VGAnyLAN

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7Passive Interface
When enabled on an interface this command allows the interface to hear routing
updates, but not repeat them. This helps to control routing updates.

8
For example, if in the devices in diagram A-1 were routers:
• Packet from Host A to Host D will have source MAC address of Host A and
destination MAC address of Router B’s local Ethernet port on Segment 1.
• Packet from Host A to Host D will have source MAC address of Router B’s
Serial port and destination MAC address of Router C’s local Serial port on
Segment 2.
• Packet from Host A to Host D will have source MAC address of Router C’s
Ethernet port and a destination MAC address of Host D on Segment 3.

If a packet sent from Host A to Host D were to be lost:
• On segment 1, Host A would rebroadcast
• On segment 2, Router B would rebroadcast
• On segment 3, Router C would rebroadcast

Bridging & LAN Switching
A View of Bridging
When non-routable protocols, such as NetBEUI, LAT or SNA were developed all
devices on a network resided locally. As networks matured and bridges were
introduced to segment LANs there was the need for these devices to communicate
across networks, especially WAN links. Because these protocols did not have the
mechanisms to allow this connectivity, bridging techniques were developed to allow
the communication between devices at the Data Link Layer (layer 2 of the OSI
model).
By default, bridging is disabled on all Cisco routers. However, these services are still
an important component of the real-world networks you will be asked to deal with in
your professional life. For the purposes of the current discussion, you will also need
to know them for the CCIE certification exams, both written and lab.
Keep in mind that many non-routable protocols, most importantly SNA, are very
time sensitive, and delays can cause loss of data or session connectivity. It is also

Routing Information Fields (RIF) are used to define paths for SRB frames to traverse
a network. They are easy to read if you understand their function. For the current
discussion it’s important that you understand how to understand how a RIF works.
Later we’ll come back to how to rip ‘um up and read ‘um.
When an SNA device needs to access a remote unit, it sends out a test frame that
attempts to find the destination. You can think of this as a broadcast in the IP
world; it isn’t, but that will help you to conceptualize.
If the destination is not found, the source device sends out a single-route or all-
routes explorer frame. Any bridges that the frame comes across in its travels add
their local bridge and ring numbers to the RIF. Eventually the frame either finds its
target or dies on the vine. IBM bridges support 8 rings and 7 bridges; IEEE 802.5
bridges support 14 bridges and 13 rings.
Once one of the explorer frames finds the destination, it returns to its creator to
announce its success. If multiple frames return, the source device takes the route of
the first frame to return, assuming this is the best path. Think of it as a race in a
maze; the first one to grab the cheese and get home first, wins.

Ripping up a RIF
This will seem complicated, but once you understand how RIFs are defined, simple
practice will drive home the necessary techniques
The first bit of the first byte of the source address is the Routing Information
Indicator (RII), which is exactly what it sounds like; it indicates that what follows is a
RIF. If this bit is a 1, the frame is a RIF; if the bit is a 0, it is not.
Here are the component parts of the first 2 bytes of a RIF, called the RCF (Routing
Control Field):
1. The first 3 bits define what kind of RIF is being examined:
• 0xx – single route frame
• 10x – all-routes explorer frame
• 11x – spanning explorer frame



From this we know:
• The RIF type is: single route frame
• The RIF Length: 8 bytes (01000 binary = 8 decimal)
• Direction to read the RIF: right-to-left
• The maximum frame length: up to 512 bytes

The rest of the RIF is called the RDF (Route Descriptor Field) and reading it is easy.
The first three digits of each two-byte grouping are the ring number (in
hexadecimal). The last digit is the bridge number (again, in hex). A zero in the
bridge number designation indicates that the destination ring has been reached.
Notice that since only four bits are used for the ring number, and zero is already
taken, the only bridge numbers available are hex 1 through F (1 to 15 in decimal).

Looking at our example again (0810.0011.0023.0040), (remember that the 0x
indicates that the number that follows is in Hex) we find that the path is:
• Ring 0x1 to bridge 0x1
• Ring 0x2 to bridge 0x3
• Ring 0x4 to the destination

Taking another example: 0A10.0021.00B1.0101.0020
Translating the first two bytes (0A10) to binary gives us: 0000.1010.0001.0000
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router (the definition of DLSw occurs later in this document).

Source-Route Transparent Bridging (SRT)

Since you now have an understanding of both TB and SRB, this next technique will
come easy. An SRT bridge looks at each frame to see if it finds a RIF (looking for the
RII). If there’s an RII, the frame is processed like SRB; if not, like TB. Some
devices, such as Windows 95 workstations do not support RIFs. SRT allows them to
communicate through bridges between LAN segments. This all takes place on Token
Ring devices. The next technique will address Ethernet translations.

Source-Route Translational Bridging (SR/TLB)

This Cisco proprietary bridging technique allows bridging to take place between
Ethernet domains and Token Ring domains. Ethernet frames are not capable of
supporting RIFs. This bridging method, when enabled on Cisco routers, handles the
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conversion from Ethernet frames to Token Ring frames (bit ordering); adjusts the
MTU sizes (default for Token Ring is 4,464 bytes, Ethernet 1.500 bytes); and adds
and removes RIFs, as necessary. To the Token Ring devices the Ethernet segment
looks like an SRB domain using a pseudo ring.

Remote-Source Route Bridging (RSRB)


networks. (Same as RSRB).
• Fast-Sequenced Transport (FTS) – This method uses IP encapsulation, which
adds some overhead, but is still connectionless. (Same as RSRB).
• Transport Control Protocol (TCP) – This method uses TCP connection, which
adds significant overhead, but ensures reliable transport. (Same as RSRB).
• Frame Relay
RIFs are generally terminated at the DLSw router. DLSw+ can support Ethernet
without SR/TLB being loaded.
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Additional tools available with DLSw+ include: Dynamic peers, peers on demand,
backup peers and the ability to load balance connections.

Encapsulated Bridging
Used to bridge over an IP Backbone or FDDI Backbone.

IRB (Integrated Routing and Bridging)
A BVI (Bridged Virtual Interface) is created that acts as a member of a bridge-group
to allow traffic to be routed. The BVI number must match the bridge-group number.

CRB (Concurrent Routing and Bridging)
Concurrent routing of one group of interfaces, while bridging another.

LAN Switching
All nodes on an Ethernet network can transmit at the same time, so the more nodes

14
• ISL – Used with Ethernet, and is Cisco Proprietary
• 802.1Q – Used with Ethernet and is IEEE standard

VTP (VLAN Transport Protocol)
VLANs definitions can span switches. VTP is the method for communicating these
definitions. Switches can be defined as:
• Server – Listens to, stores and broadcasts VLAN configurations. Can create
and delete VLANs.
• Client – Listens to configurations. Can assign ports to participating VLANs.
• Transparent – Forwards VTP traffic, but doesn’t participate in the VLANs.

CDP (Cisco Discovery Protocol)

A proprietary Data Link layer protocol used between Cisco devices to pass
information about local conditions. CDP uses a data-link, multicast address with no
protocol ID or network layer field, and cannot be filtered.
The only way to prevent their being passed is to configure “no cdp enable” on those
interfaces on which you do not want to run CDP. You can configure a MAC-layer filter
to deny a multicast address as an alternative method to block these packets.

Internet Protocol (IP)
IP is a layer-3 routed protocol that provides addressing, fragmentation and
reassembly. The minimum and maximum packet headers are 20 and 24 bytes,
respectively.
An IP address is 32 bits long, and the network and host sections are defined by the
subnet mast associate with the address.
An IP address can be bound to a host name on a router using the “ip host” command
Example: Router(config)# ip host my-example 10.10.10.1 10.10.10.2 – binds name
to both addresses