An OS image cant be displayed from a term screen.. Image is usually executec from main RAM & loaded from 1 of severAL input sources.. The OS is organizd into routines that handle tasks assoc w differnt protocols suach as data movement, table and buffer management, routing upDAtes and user command execution

SIX ROUTER MODES;:
Wheyther accessed from a console or telnet session through a tty port, a router can be placed in several modes, each providing different functions:
USER EXEC MODE; lokk only mode which user can view but not chnge
PRIVLEDGED EXEC MODE; supports debugging & testing commands, detailed exam of router, manipulation of config files and access to config modes
SETUP MODE; presents a prompted dialog mode for first time config of router
GLOBAL CONFIGURATION MODE; implement powerfiyul one line commands that perform simple config tasks
OTHER CONFIGURATION MODES; provide more detailed multi-line configs
RXBOOT MODE; a maintenance mode that yu can use to recover lost passwords

Router Status commands:
Show Version: displays config of sys hardware, software version, names and sources of config files and boot image
SHOW PROCESSES; displays info about active processes
SHOW PROTOCOLS;displays configured protocols, shows status of all layer3 protocols
SHOW MEM; shows statistica abouyt router's memory, including free memory pools
SHOW STACKS monitoors the stack use of processes and interrupt routines & displays the reason for the last sys reboot
SHOW BUFFERSprovides statistics for buffer pools on router

SHOW FLASH shows info about Flash memory device on router

SHOW RUNNING-CONFIG (write term WTF? Cisco IOS release 10.3 or earlier) - displays active config file

SHOW STARTUO-CONFIG ( show config on IOS 10.3 or earlier) displays backup config


SHOW INTERFACES displays stats for all interfaces configed on router

Show running-config & show startup-config allow an admin to see current config of router and how router will start at next reboot
You can recognize an active config by the words CURRENT CONFIGURATION at the top. U can recognize a backup config file when you see a messahe at top that tells u how much non-volatile memory you have used


Show interfaces Serial - displays configurable parameters & real-time stats related to serial ints

Show Version - command displays info about the Cisco IOS software version that is currently running on rtouter

Show Protocols - EXEC command displays the global and int specific status of any configed lkayer 3 protocol]

An OS image cant be displayed from a term screen.. Image is usually executec from main RAM & loaded from 1 of severAL input sources.. The OS is organizd into routines that handle tasks assoc w differnt protocols suach as data movement, table and buffer management, routing upDAtes and user command execution

SIX ROUTER MODES;:
Wheyther accessed from a console or telnet session through a tty port, a router can be placed in several modes, each providing different functions:
USER EXEC MODE; lokk only mode which user can view but not chnge
PRIVLEDGED EXEC MODE; supports debugging & testing commands, detailed exam of router, manipulation of config files and access to config modes
SETUP MODE; presents a prompted dialog mode for first time config of router
GLOBAL CONFIGURATION MODE; implement powerfiyul one line commands that perform simple config tasks
OTHER CONFIGURATION MODES; provide more detailed multi-line configs
RXBOOT MODE; a maintenance mode that yu can use to recover lost passwords

Router Status commands:
Show Version: displays config of sys hardware, software version, names and sources of config files and boot image
SHOW PROCESSES; displays info about active processes
SHOW PROTOCOLS;displays configured protocols, shows status of all layer3 protocols
SHOW MEM; shows statistica abouyt router's memory, including free memory pools
SHOW STACKS monitoors the stack use of processes and interrupt routines & displays the reason for the last sys reboot
SHOW BUFFERSprovides statistics for buffer pools on router

SHOW FLASH shows info about Flash memory device on router

SHOW RUNNING-CONFIG (write term WTF? Cisco IOS release 10.3 or earlier) - displays active config file

SHOW STARTUO-CONFIG ( show config on IOS 10.3 or earlier) displays backup config


SHOW INTERFACES displays stats for all interfaces configed on router

Show running-config & show startup-config allow an admin to see current config of router and how router will start at next reboot
You can recognize an active config by the words CURRENT CONFIGURATION at the top. U can recognize a backup config file when you see a messahe at top that tells u how much non-volatile memory you have used


Show interfaces Serial - displays configurable parameters & real-time stats related to serial ints

Show Version - command displays info about the Cisco IOS software version that is currently running on rtouter

Show Protocols - EXEC command displays the global and int specific status of any configed lkayer 3 protocol] that is configured on the router


Cisco Discovery Protocol: CDP provides a single proprietary command that enables net admins to access a summary of what the configs look like on other directly connected routers..

CDP runs over a data link layer that connects lower physical media and upper network layer protocols. Because it operates at L2, CDP devices that support different L3 protocols can learn about each other,

On Cisco IOS ver 10.3 or later boots, CDP starts by default and detects neighboring Cisco devices that are lso running CDP. Such devices extend beyong using TCP/IP and include directly-connected Cisco devices regardless of L3 or L4 protocol suite they run…

Each router running CDP exchanges info regarding protocol entries with its neighbors. Admins can display results of this CDP info exchange on a console that is connected to a CDP running Router

CDP Show commands

Show device identifiers – the routers configured host and somain names – if any

Show address list – at least one address for SNMP, up to one address for each supported protocol

Show port identifier – eg Ethernet 0, Ethernet and Serial 0

Show capabilities list – if device acts as a source route bridge as well as a router

Show version –

Show platform – ie Cisco 7000, 2500

Routers cache CDP info about its neighbors and releases that if any changes occur

The comand Show CDP Interface will display values of CDP timers, int staus, and encapsulation used by CDP for advertising and discovering frame transmission

Default values for timers set freq for CDP updates and for aging CDP timers. If the device receives a more recent update or if thisd hold-time value expiers, the device must discard the CDP entry

Show cdp entry (device name) to display single cached CDP entry. This shows all L3 addresses present in router . The hold time value represents elasped time since CDP frame arrived

Show cdp neighbors to display the CDP updates received on local router. Notice that for each local port the disply shows:
Neighbor device id
Local port type and #
Decremental hold-time value, in seconds
Neighbor device capability code
Neighbor hardware platform
Neighbor remote port type and #
To display the above info as well as info like from show cdp entry use the optional show cdp neighbors detail

Telnet
With Cisco’s telnet you do not need to enter command CONNECT or TELNET to est connection, just enter learned hostname
<Ctrl><shift><6><x>

To exit, EXIT or LOGOUT

Basic testing of network should procedd in sequence from one OSI layer to the next.

L7 – Telnet
L3- ping
Trace
Show IP route
L321 show interface

A successful Telnet connection indicates that upper layers as well as lower layers are working
When you can telnet one router but not another its usually due to address, naming, or access permission

PING uses ICMP Internet Control Message Protocol

Trace is similar to ping except instread of end to end connectivity, trace tests each step of the way. Trace takes advantage of the error messages generated by routers when a packet exceeds its time to live TTL value

The Trace command sends several packets and displays round trip time for both. It also tells which router on path is last to be reached – this is called fault isolation
Trace will continue until it reaches 30 hops or until escaped crtl-#### 6 esc

Network testing at the network layer with the show ip route command

The interface has 2 components - physical and logical
The hardware must make actual connection between devices and the software controls the messages that are passes

Show Flash command - to verify sufficient memory on system for IOS load

CISCO Naming Conventions:

The naming conventions for IOS Rel 11.2 contain three parts:
1 the platform
2 a letter or series of letters indentifying special capabilities and feature sets supported in image
3. specifies where inage runs and whether file is compressed

type-cap-file status

4500-2500-4700-7000 // cg-inr-aj-k
cg=comm server/remote access sever, isdn
Inr= IP subset, IPX, IBM base option
aj= APPN and Enterprise subset fro low-end/midrange
K=Enterpoirse for high-end range

i=relocatable, not compressed
m=ram, not compressed
mz=ram, compressed

COPY FLASH TFTP

U can copy or backup image to server.
1 verify file SHOW FLASH and get name of file and then COPY FLASH TFTP command to copy image to TFTP server - files can be renamed for sever

U can copy image from TFTP to flash by COPY TFTP FLASH - you will be prompted to erase stored image, often there is only room for one image
each (!) means one UDP segmejnt has xferred OK

Use the SHOW FLASH command to compare size of file to server before changing boot commands to use new image
If you need to load the backup image, use a variation of command COPY TFTP FLASH
If you copy a file that is already there u will be prompted. The first copy of file is rendered unusable in favor of newer version

----- CHapter 8

8: Individual Router Configuration Practice
8.1. Demonstrate the Ability to Fully Configure a Router from the CLI, for a Router Which Has Had Start-up Config Erased
Cold Boot Router
Ctrl + Break within 60 seconds
in 25xx routers in 16xx routers
o/r 0x2142 confreg 0x2142
i
n
enable
copy start run
config term
enable secret xxxxx
config register 0x2102
Crtl +Z
copy run start
reload
Chapter 9
9.1.1.1. List three components of the TCP/IP protocol stack.
The TCP/IP Protocol has the following components:
protocols to support ftp, e-mail, remote login, and other apps
reliable and unreliable transports
connectionless datagram (packet) delivery at the network layer
ICMP provides contrrol and message functions at the network layer
The TCP/IP suite was developed in conjunction with DARPA
TCP/IP compares closely with the lower layers of the OSI model
7 Application Application
6 Presentation Application
5 Session Application
4 Transport Transport
3 Network Internet
2 Data Link Network INterface
1 Physical Network INterface
TCP/IP info is transferred in a sequence of datagrams. One message may be transmitted as a series of datagrams that are reassembled into the message at the receiving location
TCP - connection oriented, reliable, flow control by sliding windows, reliabilty by providing sequence #s and ack, TCP resends anything that is not received and supplies a virtual circuit between end user apps...
UDP - connectionless and unreliable, although responsible for transmitting messages, no software checking. UDP provides speed because of low overhead, no acks
16bits | 16 | 32 | 32 | 4 | 6 | 6
Source Port | Dest Port | Seque # | Ack # | hlen | reserved | code bits
ACK# - next expected TCP octet
HLEN the # of 32 bit words in header
reserved - set to 0
code bits -= control functions (ie setup and termination of session)
windows - # of octets that the sender is willing to accept
checksum -
urgent pointer - indicates the end of urgent data
option = one currently defined : maximum TCP segment size
data - upper layer protocol data
port#s below 255 are for public apps // 255-1023 are assigned for marketable apps // 1023+ are unregulated
3way handshake / open connection
send SYN (seq=x)
receive SYN (seq=x)
Send SYN (seq=y,ack=x=1)
recieve SYN (seq=y,ack=x+1)
send ACK (ack=y+1)
receive ACK (ack=y+1)

UDP Segment format
16 bits | 16 | 16 | 16 | xxxxx
Source Port | Dest port | lenght | checksum | data
UDP: TFTP, SNMP, NFS, DNS
. Describe four network layer protocols from the TCP/IP stack.
IP-provides connectionless, best effort delivery routing of datagrams, not concerned with content
ICMP - provides control and messaging capabilities
ARP - determines data link layer for known IP addresses
RARP - determines netwrok addresses when datalink address is known
Diagram the IP Datagram.

|Diagram the IP Datagram.
4 | 4 | 8 | 16 | 16 | 3 | 13 | 8
vers | helen | type of service | total lenght | identification | Flags | frag offset | TTL

.1.3.1. Describe the role of host addresses on a routed network.
A host value of 0 means the wire itself
Routing tables contain entries for networks, it usually contains no info on hosts
An Ip address and a subnet mask on an interface achieve three purposes:
- enable the system to process the receipt and transmiddion of packets
- They specify the devices local addres
- they specify a range of addresees that share tha cable with the device
10.1.4.1. Describe the role of broadcast addresses on a routed network.
Directed broadcasts: Broadcasts directed into a specific network/subnet are allowed and are forwarded by the router. These directred broadcast contain all 1s in the host field (255)(FF)
Flooded broadcasts are not propagated but are considered lovcal broadcasts
10.1.5.1. Explain the assignment of router interface and network IP addresses.
The graphic shows a small network with assigned interface addresses, subnet masks, and resulting subnet numbers. The number of routing bits (network and subnet bits) in each subnet mask can also be indicated by the "/n " format.
Example /8=255.0.0.0 /24=255.255.255.0
/27=255.255.255.224
10.2.1.1. Describe ip address command.
ip address xxx.xxx.xxx.xxx(ip add) xxx.xxx.xxx.xxx (mask)


Use the " term ip netmask-format " command to specify the format of network masks for the current session. Options are:
- bit count
- dotted-decimal (default)
- hexadecimal

10.2.2.1. Describe the ip host command.
The " ip host " command makes a static name to address entry in the router's config file
name= any name you prefer to describe the destination
"tcp-port-number " optional number that idents the TCP port to use when using the host name with an EXEC connect or TELNET command. The default is port23 for telnet
" address" ip addrewss where the device can be reached

In the above example:
ip host tokyo 1.0.0.5 2.0.0.8 defines two network address for the host tokyo
ip host kyoto 1.0.0.4 defines kyoto as a name equivalent for the address 1.0.0.4
10.2.3.1. Describe the ip name-server command.
The " ip name-server" command defines which hosts can provide the name services. You can specify a max of 6 IP addresses as name servers in a single command
To map domain names to IP addresses, you must identify the host names, specify a name server, and enable DNS. Any time the OS software recieves a hostname it does not recognize, it refers to DNS to resolve that ip address oif that device


10.2.4.1. Describe how to enable and disable DNS on a router.
Each unique IP address can have a host name assoc with it. The Cisioc IOS sw maintains a cache of host name-to-address mappings for use by exec commands. This cache speeds the process of converting names to addresses.
Ip defines a na,ming scheme that allows a device to be ident by its location in IP. a name such as ftp.cisco.com idents the domain of FTP for Cisco. To keep track of domain names, IP identifes a name server that manages the name cache.

DNS is enabled by default with a server address of 255.255.255.255 which is local broadcast
The " no ip domain-lookup" command turns off name-to-address translation in the router. This means the router will not generate or forward name system broadcast packets.....

.1.3.1. Describe the role of host addresses on a routed network.
A host value of 0 means the wire itself
Routing tables contain entries for networks, it usually contains no info on hosts
An Ip address and a subnet mask on an interface achieve three purposes:
- enable the system to process the receipt and transmiddion of packets
- They specify the devices local addres
- they specify a range of addresees that share tha cable with the device
10.1.4.1. Describe the role of broadcast addresses on a routed network.
Directed broadcasts: Broadcasts directed into a specific network/subnet are allowed and are forwarded by the router. These directred broadcast contain all 1s in the host field (255)(FF)
Flooded broadcasts are not propagated but are considered lovcal broadcasts
10.1.5.1. Explain the assignment of router interface and network IP addresses.
The graphic shows a small network with assigned interface addresses, subnet masks, and resulting subnet numbers. The number of routing bits (network and subnet bits) in each subnet mask can also be indicated by the "/n " format.
Example /8=255.0.0.0 /24=255.255.255.0
/27=255.255.255.224
10.2.1.1. Describe ip address command.
ip address xxx.xxx.xxx.xxx(ip add) xxx.xxx.xxx.xxx (mask)
Use the " term ip netmask-format " command to specify the format of network masks for the current session. Options are:
- bit count
- dotted-decimal (default)
- hexadecimal

10.2.2.1. Describe the ip host command.
The " ip host " command makes a static name to address entry in the router's config file
name= any name you prefer to describe the destination
"tcp-port-number " optional number that idents the TCP port to use when using the host name with an EXEC connect or TELNET command. The default is port23 for telnet
" address" ip addrewss where the device can be reached

In the above example:
ip host tokyo 1.0.0.5 2.0.0.8 defines two network address for the host tokyo
ip host kyoto 1.0.0.4 defines kyoto as a name equivalent for the address 1.0.0.4
10.2.3.1. Describe the ip name-server command.
The " ip name-server" command defines which hosts can provide the name services. You can specify a max of 6 IP addresses as name servers in a single command
To map domain names to IP addresses, you must identify the host names, specify a name server, and enable DNS. Any time the OS software recieves a hostname it does not recognize, it refers to DNS to resolve that ip address oif that device
10.2.4.1. Describe how to enable and disable DNS on a router.
Each unique IP address can have a host name assoc with it. The Cisioc IOS sw maintains a cache of host name-to-address mappings for use by exec commands. This cache speeds the process of converting names to addresses.
Ip defines a na,ming scheme that allows a device to be ident by its location in IP. a name such as ftp.cisco.com idents the domain of FTP for Cisco. To keep track of domain names, IP identifes a name server that manages the name cache.
DNS is enabled by default with a server address of 255.255.255.255 which is local broadcast
The " no ip domain-lookup" command turns off name-to-address translation in the router. This means the router will not generate or forward name system broadcast packets.....
The show hosts command is used to display cached host names and addresses

Show Hosts commands:
host names of learned hosts
flag descriptions of how info was learned and current status
perm statitcally configured
temp dns configured
ok entry is current
EX entry expired
age time in hours since software reffered the entry
type protocol field
addresses logical addresses assoc with hoist name

3 comands used to verify address config

telnet verifies app layer software
ping uses ICMP to verify hardware connection
trace uses TTL values to generate medssagesa from each router on path

PING values ! successful, . timed out , U dest unreach, C congestion-experienced packet, I ping interuppted (e.g. Ctrl-Shjift-6 x), ? packet tpye unknown, & packett TTL exceeded

Extended PING - only avail in EXEC mode - used in extended mode to specify Internet header options. To enter extended mode, type ping and Y at extended command prompt


TRACE Supported by IP,CLNS,VINES, and appl;e talk

responses : !H probe was received by router but not forwarded, usually due to an access list, P protocol was unreachable, N- the network was unreachable, U port was unreachable, * time out

Internetworking functions of the network layer include network addressing and best path selection for traffic

In network addressing, one part of the address is used to identify the path used by the router and the other is used for ports or devices on the network

Routed protocols allow routers to direct user traffic; routing protocols work between routers to maintain path tables

Network discovery for distance-vectoe routing involves exchange of routing tables; problems can include slow convergence

For link-state routing, routers calculate shortest paths to other routers; problems can include inconsistant updates

Balanced hybrid routing uses uses attribs of both link state and distance-vector routing, and can apply paths to several protocols

Path determination for traffic going through a network cloud, occurs at the network layer. The path determination function enables a router to evaluate the available paths to a dest and to est the preffered handling of a packet

Routing services use network topology info when evaluating network paths. This info can be configured by the administer or collected through dynamic process running in the network

The net layer interfaces to networks and provides best-effort end-to-end packet delivery services to its user, the transport layer. The net layer uses the ip routing table to send packets from the source network to the dest network

After the router determines which path to use, it proceeded with forwarding the packet. It takes the packet that it accepted on one interface and forwards it to another interface ot port that reflects the best path to the packet's destination

11.1.3.1. Explain how routers route packets from source to destination.
To be truly practical, a network must consistently represent the paths available between the routyers.
Using these addresses the net layer can provide a relay connection that interconnects independent networks

The consistency of L3 addresses accross the entire network also improves bandwidth by preventing unnecessaruy broadcasts. Broadcasts invoke unnecessary process overheadd and waste capacity on any devices or links that do not need to receive the broadcast...

By using consistent end-to-end addressing to represent the path of media connections, the network layer can find a path to the dest without unneceesarily burdening the devices or links on the internetwork with broadcasts

11.1.4.1. Explain that both networks and individual hosts on a network must have addresses.
The 11.1.5.1. Explain best path selection and packet switching as the two basic processes of a router.
A router generally relays a packet from one data link to another, using two basic functions, a path

Internetworking functions of the network layer include network addressing and best path selection for traffic
In network addressing, one part of the address is used to identify the path used by the router and the other is used for ports or devices on the network
Routed protocols allow routers to direct user traffic; routing protocols work between routers to maintain path tables
Network discovery for distance-vectoe routing involves exchange of routing tables; problems can include slow convergence
For link-state routing, routers calculate shortest paths to other routers; problems can include inconsistant updates
Balanced hybrid routing uses uses attribs of both link state and distance-vector routing, and can apply paths to several protocols
Path determination for traffic going through a network cloud, occurs at the network layer. The path determination function enables a router to evaluate the available paths to a dest and to est the preffered handling of a packet
Routing services use network topology info when evaluating network paths. This info can be configured by the administer or collected through dynamic process running in the network
The net layer interfaces to networks and provides best-effort end-to-end packet delivery services to its user, the transport layer. The net layer uses the ip routing table to send packets from the source network to the dest network
After the router determines which path to use, it proceeded with forwarding the packet. It takes the packet that it accepted on one interface and forwards it to another interface ot port that reflects the best path to the packet's destination
11.1.3.1. Explain how routers route packets from source to destination.
To be truly practical, a network must consistently represent the paths available between the routyers.
Using these addresses the net layer can provide a relay connection that interconnects independent networks
The consistency of L3 addresses accross the entire network also improves bandwidth by preventing unnecessaruy broadcasts. Broadcasts invoke unnecessary process overheadd and waste capacity on any devices or links that do not need to receive the broadcast...
By using consistent end-to-end addressing to represent the path of media connections, the network layer can find a path to the dest without unneceesarily burdening the devices or links on the internetwork with broadcasts
11.1.4.1. Explain that both networks and individual hosts on a network must have addresses.
The 11.1.5.1. Explain best path selection and packet switching as the two basic processes of a router.
A router generally relays a packet from one data link to another, using two basic functions, a path

11.2.4.1. Explain why dynamic routing is necessary.
11.2.5.1. Explain what information is important in dynamic routing.
The success of dynamic routing depends on 2 basic router functions:
maintenance of a routing table
timely distribution of knowledge, in the form of routing updates, to other routers
Dynamic routing relies on a routing protocol to share knowledge among routers. A routing protocol defines the set of rules used by a router when it communications with neighboring routers. A routing protocol describes:
- how to send updates
- what knowledge is contained in these updates
- when to send this knowledge
- how to locate recipients of the updates
11.2.6.1. Explain how distances on network paths are determined by
various metrics.
When a routing algorithm updates A routing table, its primary objective is to determine the best info to include i the table. Each routing algorithm interprets what is best in its own way. The algorithm generates a number, called the metric value, for each path through the network. TypicLLy the smaller the metric number, the better the path.
You can calculate metrics based on a single characteristic of a path; you can calculate more complex metrics by combining several characteristics. The metrics most comm only used by routers are;
bandwidth- the capacity of a link
delay - the lenght of time required to move a packet along each linik from soutrce to dest
load - the amount of activity on a network resource such as a router
reliability - usually refers to the error rate of each network link
hop count - th # of routers a packet must pass through before reaching its dest
ticks - the delay on a data link using IBM pc clock ticks (approx 55 milliseconds)
cost- an arbritary value, usually based on bandwidth, monetaRY EXPENSE, OR OTHER measurements, that is assigned by a network administrator
11.2.7.1. Describe three classes of routing protocols.
Most routing algorithms can be classified as onre of two basic algorithms - distance vector or link state. The distance-vector routing approach determines the direction (vector) and distance to any link in the internetwork. The link-state (also called shortest path first) approach re-creates the exact topology of the entire internetwork (or at least the partition in which the router is situated)

The balanced hybrid approach combines aspects of link-state and dist-vect algos. The next several pages cover procedures and present techniques for minimizing the problems)

www.webproforum.com/vpn

11.2.8.1. Explain the concept of time to convergence.
The routing algo is fundamental to dynamic routing. Whenever the topology of a network changes because of groeth, reconfig, or failure, the network knowledge base must also change...
The knowledge needs to reflect an accurate, consistent view of the new topology. The view is called convergence . When all routers in a internetwork are operating with the same knowledge, the internetwork is said to have converged.

Fast convergence is a desireable network feature because it recduces the period of time in which routers would continue to make incorrect/wasteful routing decisions

11.3.1.1. Explain the concept of distance-vector routing.

Distance-vector based routing algos (alos known as Bellman-Ford) pass periodic copies of a routing table fronm router to router. These regular uopdates between routers communicate topology changes.

Each router receives a routing table from its directly neighboring routers. The algo eventually accumulates network distances so that it caN maintian a database of network topology info.

11.3.6.1. Explain the solution of defining a maximum.
Distance vector routing algos are self correcting but a loop problem can require a count to infinity. DVprots define infinity as a specific max#. This # refers toa routing metric
Split Horizon - will prevent certain routers from saying a path (incorrect) is available via another router

hold down timer -

11.4.1.1. Explain the concept of link-state routing.
LINK STATE- uses SPF algos, where they maintaIN a complex database of topology info. Link-state maintianins full knowledge of distant routers and how they interconnect
Link-state routing uses;
link-state advertisements (LSAs)
a topological databse
the SPF algo and the resulting SPF tree
a routing table of paths and ports to each network
11.4.2.1. Explain how link-state protocols exchange routing tables.
routers exchange LSAs with each other
each router in paralell with the others constructs a topological database consitsing of all LSAs
the SPF compoutes network reachability
the router lists its best paths and the ports to these dest nets. It also maintianins a db of topologies and status details
11.4.3.1. Explain how topology changes propagate through the
network of routers.