telnet | madrock

Don’t underestimate the value of standards for your infrastructure, website configuration, database engine configuration/architecture,staging environment and development/QA environments.

Some thoughts:

Many don’t lock accounts after X failed logins, this is normally done for good customer service, but leaves the system vulnerable.

– And all the other things expected for a remote login session (forced password changes, aging, etc))
– Tools such as Brutus may be use to brute force hack authenticated sessions.

Many allow session sequence numbers to be incremented, allowing an authenticated user to view other customer session.

– These may be server side, client side, cookie based, etc.
– Get someone to check the development methodologies and the code being used.
– Database query strings can be placed into test entry fields, allowing table dumps to browser.
– Check all pages served are secure and contain user authentication flags.

Customer data may not be segregated, this needs to be checked.
Customer data should not reside on the Web Server.

Authentication databases / system data should not reside on the webserver.
The databases should reside on a private/semi-private network.

– A different segment to the main banking system.

Webserver should be dual homed or equivalent (some VLAN techniques are good)

– Separate private and public network cards, monitoring/backup/administration
– Infrastructure set-up to explicitly deny inbound/outbound ports, private IP & monitoring escaping from the network.

At all data segregation points ensure rules are in place which appreciates the traffic though that point.

All customer data where possible should be sourced from a secure back-end database.

– This may be a staging environment. i.e. no the main banking system.
– This usually allows for transactions to appear real time to the customer.
– Many transactions may be batched in reality. (internal or external to the bank)

Ensure suitable rules have been set-up on firewalls.

– There should be inbound and outbound rules on firewalls and filtering routers.

Don’t allow any infrastructure on the front end to allow remote administrative connections. (telnet, etc.)

– Use the serial console port to connect to a server or back-end terminal server.

Look for the segregation / staging of online customer content from main banking systems

Ensure that a separate development / QA / production environment system and suitable process is in place.

Services not used by the system are active

– These should be disabled.

Port scan of the supporting infrastructure (routers /switches) and server(s).

– Investigate the reasons for all open ports.

Don’t use the main gateway for trusted partner access (clearing / RAS / etc.)
Do all that standard IIS checks and NT checks (Sample scripts, change management, patching methodologies, etc.)
Ensure denial of service precaution have been taken into account for all infrastructure and server equipment.
Check the adequacy of the escalation procedures used.

– Look for real-time monitoring and alerting.
– Look for responsibility matrix.
– Look for ownership of issues.

Consider upstream carrier(s) vulnerability (denial of service, IP spoofing, DNS hacking, etc)
Consider social engineering of customer, administrative, partner accounts / systems / infrastructure.

– Helpdesk procedures and policies and/or alternate technologies (Caller ID, Gateway IP, etc.).

Use dynamic passwords where possible (SecureID, TACACS, etc.).
Use encrypted tunnelling where needed (IPSec, Firewall 1, etc)
Consider looking at other customer authentication methods to enhance existing methods.

– Digital cert, IP address locked to account, etc.
– Consider use of CVV or CVN for bank issued cards.

Consider how passwords are distributed /changed for customers.

– Plain text email, telephone, etc.
– Can passwords be changed online?

Is additional authentication used between sections of the services once authenticated?
Consider what the customer has access to once authenticated.

– Look at SWIFT, RTGS, inter-bank transfers, access to credit cards, etc.
– If an attacker does get in, what can the do?

Use techniques to ensure pages, customer details are not cached at ISP, or client system.

– These are flags that can be set within pages.
– Normally SSL is cached, but some proxy vendors have been playing with techniques to do so.
– Caching of SSL pages on the client system can be turned on on some browsers.
– May banks use a Java (or similar) applet for all customer interaction, restricting all caching issues.

Ensure paper based and on-line liability clauses are available are address all effected areas.
Ensure within the customer sign-up process banking liability is reduced.

– I’ve seen statements like “use this system at your own risk, responsibility for any liability or claim will NOT……”
– Not very customer focused, but that’s what their legal department recommended.

All of the above can effect the security and/or operation of an on-line banking system.

Other things to consider:

External development and support of the application.
Ownership and management of the hardware/applications
Publishing points for new content (internal/private/trusted network or Internet)
Topology of front end.Â i.e. Security Architecture document should be in place and managed appropriately.
Are limited AP tests performed whenever changes are made to the environment? i.e. integrated AP into Change management process.
Database access. Is it buffered or is it live to the core banking systems.
What facilities are provided? Direct debit + Credit Card + SWIFT + ……. Consider different scenarios for your attack depending on the feature.
What other services are shared within the network segment that the Internet Banking service is running. Can this be used to compromise the Internet Banking site. eg. different support/business/development organisations with differing security strategies/profiles.
Consider all external supporting services within you AP. Look at internal/external DNS poisoning opportunities, mail relay, etc. What IPS’s do they use has the ISP any opportunity to access systems or supporting services which may affect Internet Banking.
Depending on the size of the Bank, many organisation do not use the same support groups for infrastructure and the application. As a result external connections to the infrastructure may be provided for an external support organisation to administer the infrastructure.
Look at the business and user authentication methods and paths (client side certs, secure ID, SMART Card, etc). Consider two factor authentication and modern user identification methods. eg. what is your favourite food in addition to normal usernames and passwords. Do system administration staff use dynamic passwords (secureID, etc)?
See if the Internet Banking application sends email to users which may contain interesting information.
Better access to the application can generally be gained after access to the system. i.e. get an legitimate account on the system. I have found that some sample/administration screens have been restricted to authenticated users only.
Consider social engineering the Help desk to have an account password reset.

Cisco Command Cheat Sheet

Posted by :Derek On : July 4, 2008

Category: Infrastructure, Internet

Tags:access, authentication, authentification, boot system, broadcast, cisco commands, data, DES, DNS, domain name services, EFT, encapsulation, Ethernet, frequency, hack, Infrastructure, interface, ISP, name server, network, password, phone, pvc, Relay, SAP, script, security, server, Shiraz, telnet, text, trunk, type

I found a list of useful Cisco commands which I though I would post here.

ROUTER COMMANDS `:`

Config# terminal editing – allows for enhanced editing commands
Config# terminal monitor – shows output on telnet session
Config# terminal ip netmask-format hexadecimal|bit-count|decimal – changes the format of subnet masks

HOST NAME:

Config# hostname ROUTER_NAME

BANNER:

Config# banner motd # TYPE MESSAGE HERE # – # can be substituted for any character, must start and finish the message

DESCRIPTIONS:

Config# description THIS IS THE SOUTH ROUTER – can be entered at the Config-if level

CLOCK:

Config# clock timezone Central -6
# clock set hh:mm:ss dd month yyyy – Example: clock set 14:13:00 25 August 2003

CHANGING THE REGISTER:

Config# config-register 0x2100 – ROM Monitor Mode
Config# config-register 0x2101 – ROM boot
Config# config-register 0x2102 – Boot from NVRAM

BOOT SYSTEM:

Config# boot system tftp FILENAME SERVER_IP – Example: boot system tftp 2600_ios.bin 192.168.14.2
Config# boot system ROM
Config# boot system flash – Then – Config# reload

CDP:

Config# cdp run – Turns CDP on
Config# cdp holdtime 180 – Sets the time that a device remains. Default is 180
Config# cdp timer 30 – Sets the update timer.The default is 60
Config# int Ethernet 0
Config-if# cdp enable – Enables cdp on the interface
Config-if# no cdp enable – Disables CDP on the interface
Config# no cdp run – Turns CDP off

HOST TABLE:

Config# ip host ROUTER_NAME INT_Address – Example: ip host lab-a 192.168.5.1
-or-
Config# ip host RTR_NAME INT_ADD1 INT_ADD2 INT_ADD3 – Example: ip host lab-a 192.168.5.1 203.23.4.2 199.2.3.2 – (for e0, s0, s1)

DOMAIN NAME SERVICES:

Config# ip domain-lookup – Tell router to lookup domain names
Config# ip name-server 122.22.2.2 – Location of DNS server
Config# ip domain-name cisco.com – Domain to append to end of names

CLEARING COUNTERS:

# clear interface Ethernet 0 – Clears counters on the specified interface
# clear counters – Clears all interface counters
# clear cdp counters – Clears CDP counters

STATIC ROUTES:

Config# ip route Net_Add SN_Mask Next_Hop_Add – Example: ip route 192.168.15.0 255.255.255.0 205.5.5.2
Config# ip route 0.0.0.0 0.0.0.0 Next_Hop_Add – Default route
-or-
Config# ip default-network Net_Add – Gateway LAN network

IP ROUTING:

Config# ip routing – Enabled by default
Config# router rip
-or-
Config# router igrp 100
Config# interface Ethernet 0
Config-if# ip address 122.2.3.2 255.255.255.0
Config-if# no shutdown

IPX ROUTING:

Config# ipx routing
Config# interface Ethernet 0
Config# ipx maximum-paths 2 – Maximum equal metric paths used
Config-if# ipx network 222 encapsulation sap – Also Novell-Ether, SNAP, ARPA on Ethernet. Encapsulation HDLC on serial
Config-if# no shutdown

ACCESS LISTS:

IP Standard	1-99
IP Extended	100-199
IPX Standard	800-899
IPX Extended	900-999
IPX SAP Filters	1000-1099

IP STANDARD:

Config# access-list 10 permit 133.2.2.0 0.0.0.255 – allow all src ip’s on network 133.2.2.0
-or-
Config# access-list 10 permit host 133.2.2.2 – specifies a specific host
-or-
Config# access-list 10 permit any – allows any address
Config# int Ethernet 0
Config-if# ip access-group 10 in – also available: out

IP EXTENDED:

Config# access-list 101 permit tcp 133.12.0.0 0.0.255.255 122.3.2.0 0.0.0.255 eq telnet
-protocols: tcp, udp, icmp, ip (no sockets then), among others
-source then destination address
-eq, gt, lt for comparison
-sockets can be numeric or name (23 or telnet, 21 or ftp, etc)
-or-
Config# access-list 101 deny tcp any host 133.2.23.3 eq www

-or-

Config# access-list 101 permit ip any any
Config# interface Ethernet 0
Config-if# ip access-group 101 outIPX STANDARD:
Config# access-list 801 permit 233 AA3 – source network/host then destination network/host

-or-

Config# access-list 801 permit -1 -1 – “-1” is the same as “any” with network/host addresses
Config# interface Ethernet 0
Config-if# ipx access-group 801 outIPX EXTENDED:
Config# access-list 901 permit sap 4AA all 4BB all
– Permit protocol src_add socket dest_add socket
-“all” includes all sockets, or can use socket numbers

-or-

Config# access-list 901 permit any any all any all
-Permits any protocol with any address on any socket to go anywhere
Config# interface Ethernet 0
Config-if# ipx access-group 901 inIPX SAP FILTER:
Config# access-list 1000 permit 4aa 3 – “3” is the service type

-or-

Config# access-list 1000 permit 4aa 0 – service type of “0” matches all services
Config# interface Ethernet 0
Config-if# ipx input-sap-filter 1000 – filter applied to incoming packets

-or-

Config-if# ipx output-sap-filter 1000 – filter applied to outgoing packets

NAMED ACCESS LISTS:

Config# ip access-list standard LISTNAME
-can be ip or ipx, standard or extended
-followed by the permit or deny list
Config# permit any
Config-if# ip access-group LISTNAME in
-use the list name instead of a list number
-allows for a larger amount of access-lists

PPP SETUP:

Config-if# encapsulation ppp
Config-if# ppp authentication chap pap
-order in which they will be used
-only attempted with the authentification listed
-if one fails, then connection is terminated
Config-if# exit
Config# username Lab-b password 123456
-username is the router that will be connecting to this one
-only specified routers can connect

-or-

Config-if# ppp chap hostname ROUTER
Config-if# ppp chap password 123456
-if this is set on all routers, then any of them can connect to any other
-set same on all for easy configuration

ISDN SETUP:

Config# isdn switch-type basic-5ess – determined by telecom
Config# interface serial 0
Config-if# isdn spid1 2705554564 – isdn “phonenumber” of line 1
Config-if# isdn spid2 2705554565 – isdn “phonenumber” of line 2
Config-if# encapsulation PPP – or HDLC, LAPD

DDR – 4 Steps to setting up ISDN with DDR Configure switch type

1. Config# isdn switch-type basic-5ess – can be done at interface config

2. Configure static routes
Config# ip route 123.4.35.0 255.255.255.0 192.3.5.5 – sends traffic destined for 123.4.35.0 to 192.3.5.5
Config# ip route 192.3.5.5 255.255.255.255 bri0 – specifies how to get to network 192.3.5.5 (through bri0)

3. Configure Interface
Config-if# ip address 192.3.5.5 255.255.255.0
Config-if# no shutdown
Config-if# encapsulation ppp
Config-if# dialer-group 1 – applies dialer-list to this interface
Config-if# dialer map ip 192.3.5.6 name Lab-b 5551212
connect to lab-b at 5551212 with ip 192.3.5.6 if there is interesting traffic
can also use “dialer string 5551212” instead if there is only one router to connect to

4. Specify interesting traffic
Config# dialer-list 1 ip permit any
-or-
Config# dialer-list 1 ip list 101 – use the access-list 101 as the dialer list

5. Other Options
Config-if# hold-queue 75 – queue 75 packets before dialing
Config-if# dialer load-threshold 125 either
-load needed before second line is brought up
-“125” is any number 1-255, where % load is x/255 (ie 125/255 is about 50%)
-can check by in, out, or either

Config-if# dialer idle-timeout 180
-determines how long to stay idle before terminating the session
-default is 120

FRAME RELAY SETUP:

Config# interface serial 0
Config-if# encapsulation frame-relay – cisco by default, can change to ietf
Config-if# frame-relay lmi-type cisco – cisco by default, also ansi, q933a
Config-if# bandwidth 56
Config-if# interface serial 0.100 point-to-point – subinterface
Config-if# ip address 122.1.1.1 255.255.255.0
Config-if# frame-relay interface-dlci 100
-maps the dlci to the interface
-can add BROADCAST and/or IETF at the end
Config-if# interface serial 1.100 multipoint
Config-if# no inverse-arp – turns IARP off; good to do
Config-if# frame-relay map ip 122.1.1.2 48 ietf broadcast
-maps an IP to a dlci (48 in this case)
-required if IARP is turned off
-ietf and broadcast are optional
Config-if# frame-relay map ip 122.1.1.3 54 broadcast

SHOW COMMANDS

Show access-lists – all access lists on the router
Show cdp – cdp timer and holdtime frequency
Show cdp entry * – same as next
Show cdp neighbors detail – details of neighbor with ip add and ios version
Show cdp neighbors – id, local interface, holdtime, capability, platform portid
Show cdp interface – int’s running cdp and their encapsulation
Show cdp traffic – cdp packets sent and received
Show controllers serial 0 – DTE or DCE status
Show dialer – number of times dialer string has been reached, other stats
Show flash – files in flash
Show frame-relay lmi – lmi stats
Show frame-relay map – static and dynamic maps for PVC’s
Show frame-relay pvc – pvc’s and dlci’s
Show history – commands entered
Show hosts – contents of host table
Show int f0/26 – stats of f0/26
Show interface Ethernet 0 – show stats of Ethernet 0
Show ip – ip config of switch
Show ip access-lists – ip access-lists on switch
Show ip interface – ip config of interface
Show ip protocols – routing protocols and timers
Show ip route – Displays IP routing table
Show ipx access-lists – same, only ipx
Show ipx interfaces – RIP and SAP info being sent and received, IPX addresses
Show ipx route – ipx routes in the table
Show ipx servers – SAP table
Show ipx traffic – RIP and SAP info
Show isdn active – number with active status
Show isdn status – shows if SPIDs are valid, if connected
Show mac-address-table – contents of the dynamic table
Show protocols – routed protocols and net_addresses of interfaces
Show running-config – dram config file
Show sessions – connections via telnet to remote device
Show startup-config – nvram config file
Show terminal – shows history size
Show trunk a/b – trunk stat of port 26/27
Show version – ios info, uptime, address of switch
Show vlan – all configured vlan’s
Show vlan-membership – vlan assignments
Show vtp – vtp configs

CATALYST COMMANDS
For Native IOS – Not CatOS

SWITCH ADDRESS:

Config# ip address 192.168.10.2 255.255.255.0
Config# ip default-gateway 192.168.10.1DUPLEX MODE:
Config# interface Ethernet 0/5 – “fastethernet” for 100 Mbps ports
Config-if# duplex full – also, half | auto | full-flow-control

SWITCHING MODE:

Config# switching-mode store-and-forward – also, fragment-free

MAC ADDRESS CONFIGS:

Config# mac-address-table permanent aaab.000f.ffef e0/2 – only this mac will work on this port
Config# mac-address-table restricted static aaab.000f.ffef e0/2 e0/3
-port 3 can only send data out port 2 with that mac
-very restrictive security
Config-if# port secure max-mac-count 5 – allows only 5 mac addresses mapped to this port

VLANS:

Config# vlan 10 name FINANCE
Config# interface Ethernet 0/3
Config-if# vlan-membership static 10TRUNK LINKS:
Config-if# trunk on – also, off | auto | desirable | nonegotiate
Config-if# no trunk-vlan 2
-removes vlan 2 from the trunk port
-by default, all vlans are set on a trunk port

CONFIGURING VTP:
Config# delete vtp – should be done prior to adding to a network
Config# vtp server – the default is server, also client and transparent
Config# vtp domain Camp – name doesn’t matter, just so all switches use the same
Config# vtp password 1234 – limited security
Config# vtp pruning enable – limits vtp broadcasts to only switches affected
Config# vtp pruning disableFLASH UPGRADE:
Config# copy tftp://192.168.5.5/configname.ios opcode – “opcode” for ios upgrade, “nvram” for startup config

DELETE STARTUP CONFIG:

Config# delete nvram

BGP:

show ip bgp – Displays entries in the BGP routing table.
show ip bgp injected-paths – Displays paths in the BGP routing table that were conditionally injected.
show ip bgp neighbors – Displays information about the TCP and BGP connections to neighbors.

BGP Conditional Route Injection:

Step 1 Router(config)# router bgp as-number
-Â Places the router in router configuration mode, and configures the router to run a BGP process.

Step 2 Router(config-router)# bgp inject-map ORIGINATE exist-map LEARNED_PATH
-Â Configures the inject-map named ORIGINATE and the exist-map named LEARNED_PATH for conditional route injection.

Step 3 Router(config-router)# exit
-Exits router configuration mode, and enters global configuration mode.

Step 4 Router(config)# route-map LEARNED_PATH permit sequence-number
– Configures the route map named LEARNED_PATH.

Step 5 Router(config-route-map)# match ip address prefix-list ROUTE
– Specifies the aggregate route to which a more specific route will be injected.

Step 6 Router(config-route-map# match ip route-source prefix-list ROUTE_SOURCE
– Configures the prefix list named ROUTE_SOURCE to redistribute the source of the route.
Note The route source is the neighbor address that is configured with the neighbor remote-as command. The tracked prefix must come from this neighbor in order for conditional route injection to occur.

Step 7 Router(config-route-map)# exit
– Exits route-map configuration mode, and enters global configuration mode.

Step 8 Router(config)# route-map ORIGINATE permit 10
– Configures the route map named ORIGINATE.

Step 9 Router(config-route-map)# set ip address prefix-list ORIGINATED_ROUTES
– Specifies the routes to be injected.

Step 10 Router(config-route-map)# set community community-attribute additive
– Configures the community attribute of the injected routes.

Step 11 Router(config-route-map)# exit
– Exits route-map configuration mode, and enters global configuration mode.

Step 12 Router(config)# ip prefix-list ROUTE permit 10.1.1.0/24
– Configures the prefix list named ROUTE to permit routes from network 10.1.1.0/24.

Step 13 Router(config)# ip prefix-list ORIGINATED_ROUTES permit 10.1.1.0/25
– Configures the prefix list named ORIGINATED_ROUTES to permit routes from network 10.1.1.0/25.

Step 14 Router(config)# ip prefix-list ORIGINATED_ROUTES permit 10.1.1.128/25
– Configures the prefix list named ORIGINATED_ROUTES to permit routes from network 10.1.1.0/25.

Step 15 Router(config)# ip prefix-list ROUTE_SOURCE permit 10.2.1.1/32
– Configures the prefix list named ROUTE_SOURCE to permit routes from network 10.2.1.1/32.
Note The route source prefix list must be configured with a /32 mask in order for conditional route injection to occur.

DHCP

Step 1 (config)# interface ethernet0/0
(config-if)#ip address 1.1.1.1 255.0.0.0
(config-if)# no shutdown
– Configure an IP address on the router’s Ethernet port, and bring up the interface. (On an existing router, you would have already done this.)

Step 2 (config)# ip dhcp pool mypool
– Create a DHCP IP address pool for the IP addresses you want to use.

Step 3 (dhcp-config)# network 1.1.1.0 /8
– Specify the network and subnet for the addresses you want to use from the pool.

Step 4 (dhcp-config)#domain-name mydomain.com
– Specify the DNS domain name for the clients.

Step 5 (dhcp-config)#dns-server 1.1.1.10 1.1.1.11
– Specify the primary and secondary DNS servers.

Step 6 (dhcp-config)#default-router 1.1.1.1
– Specify the default router (i.e., default gateway).

Step 7 (dhcp-config)#lease 7
– Specify the lease duration for the addresses you’re using from the pool.

Step 8 (dhcp-config)#exit
– Exit Pool Configuration Mode.

This takes you back to the global configuration prompt.

Next, exclude any addresses in the pool range that you don’t want to hand out.

For example, let’s say that you’ve decided that all IP addresses up to .100 will be for static IP devices such as servers and printers. All IP addresses above .100 will be available in the pool for DHCP clients.

Here’s an example of how to exclude IP addresses .100 and below:

Optional (config)#ip dhcp excluded-address 1.1.1.0 1.1.1.100

The full DHCP reference can be found on the CISCO site.

Common Commands and Troubleshooting

Set a password on the console line:
- configure terminal
- line console 0
- password â€˜ciscoâ€™
- login
Passwords are case sensitive.
You must configure a password on the VTY lines, without one no one will be able to telnet to the switch/router.
The default mode when logging into a switch/router via telnet or SSH is user exec mode, which is indicated by the â€˜>â€™ prompt.
To configure the switch/router you need to use the privileged EXEC mode. To do this you enter the enable command in user EXEC mode. The prompt is indicated with â€˜#â€™.
If both enable secret and enable password are set, the enable secret will be used.
The enable secret is encrypted (by default) where as the enable password is in clear text.
In a config containing an enable secret 5 â€˜hashâ€™ the 5 refers to the level of encryption being used.
If no enable password/secret has been set when someone telnets to the device, they will get a â€˜%No password setâ€™ message. Someone with physical access must set the password.
To place all telnet users directly into enable mode:
- configure terminal
- line vty 0 4
- privilege level 15
To put a specific user directly into privileged EXEC mode (enable mode)
- username superman privilege 15 password louise
Telnet sends all data including passwords in clear text which can be intercepted.
SSH encrypts all data preventing an attacker from intercepting it.
Setting up a local user/password login database for use with telnet:
- configure terminal
- line vty 0 4
- login local
- exit
- username telnetuser1 password secretpass
To set up SSH you need to create the local user database, the domain name must be specified with the ip domain-name command and a crypto key must be created with the crypto key generate rsa command. To enable SSH on the VTY lines, use the command transport input ssh.
If you connect two Cisco switches together and the lights donâ€™t go amber then green, but instead stays off. A straight through cable has been used instead of a crossover cable.
The term â€˜a switches management interfaceâ€™ normally refers to VLAN1.
Assign a default gateway using the ip default-gateway ipaddress command.
You can use the command interface range fasterthernet 0/1 â€“ 12 to select a range of interfaces to configure at once.
MOTD banner appears before login prompt.
The login banner appears before the login prompt but after the MOTD banner.
The banner exec appears after a successful logon.
line con 0 â€“ configuring the logging synchronous on the console port stops the router from displaying messages (like an interface state change) until it detects no input from the keyboard and not other output from the router, such as a show commands output.
exec-timeout x y (x=minutes, y=seconds) â€“ the default is 5 minutes. Can be disabled by setting x=0 y=0
Shortcut commands
- Up Arrow â€“ will show you the last command you entered. Control+P does the same thing.
- Down Arrow â€“ will bring you one command up in the command history. Control+N does the same thing.
- CTRL+A takes the cursor to the start of the current command.
- CTRL+E takes the cursor to the end of the current command.
- Left arrow or CTRL+B moves backwards (towards the start) of the command one character at a time.
- Right arrow or CTRL+P moves forwards (towards the end) of the command one character at a time.
- CTRL+D deletes one character (the same as backspace).
- ESC+B moves back one word in the current command.
- ESC+F moves forward one word in the current command.
show history command will show the last 10 commands run by default.
the history size can be increased individually on the console port and on the VTY lines with the history size x command.
Config modes
- config t R1<config> is the global configuration mode.
- line vty 0 4 R1<config-line> is the line config mode.
- interface fastethernet 0/1 R1<config-if> interface config mode.

Troubleshooting

Cisco Discovery Protocol (CDP) runs by default on Cisco routers and switches. It runs globally and on a per-interface level.
CDP discovers basic information about neighboring switches and routers.
On media that supports multicasts at the data link layer, CDP uses multicast frames. on other media, CDP sends a copy of the CDP update to any known data-link addresses.
The show cdp command shows CDP settings.
CDP can be disabled globally using the command no cdp run and re-enable using cdp run.
CDP can be disabled at an interface level using the no cdp enable command at the sub-interface level.
The command show cdp neighbor – lists one summary line of information about each neighbor. Including:
- Device ID â€“ the remote devices hostname.
- Local Interface â€“ the local switch/router interface connected to the remote host.
- Holdtime â€“ is the number of seconds the local device will retain the contents of the last CDP advertisement received from the remote host.
- Capability â€“ shows you the type of device the remote host is.
- Platform â€“ is the remote devices hardware platform.
- Port ID â€“ is the remote interface on the direct connection.
The command show cdp neighbor detail â€“ lists one large set (approx 15 lines) of information, one set for every neighbor. Including:
- The IOS version.
- VTP management domain.
- Management addresses.
show cdp entry name – lists the same information as the show cdp neighbors detail command, but only for the named neighbor (case sensitive).
show cdp â€“ states whether CDP is enabled globally, and lists the default update and holdtime timers.
show cdp traffic â€“ lists global statistics for the number of CDP advertisements sent and received.
show cdp interface type number – states whether CDP is enabled on each interface or a single interface if the interface is listed, and states the update and holdtime timers on those interfaces.
CDP should be disabled on interfaces it is not needed to limit risk of an attacker learning details about each switch or router. Use the no cdp enable interface subcommand to disable CDP and the cdp enable interface subcommand to re-enable it.
The command show cdp interface shows the CDP settings for every interface.
Interface status messages:
- Interface status is down/down â€“ this indicates a physical problem, most likely a loose or unplugged cable.
- Line protocol is down, up/down â€“ this indicates a problem at the logical level, most likely an encapsulation mismatch or a missing clock rate.
- Administratively down â€“ this indicates the interface has been shutdown and needs to be manually opened with the sub interface command no shutdown.
The command show mac-address-table shows the mac address table. show mac-address-table dynamic sows the dynamically learned entries only.
Most problems on a switch are caused by human error â€“ misconfiguration.
The command show debugging shows all the currently running debugs.
undebug all â€“ will turn all debugging off.
The command show vlan brief shows a switches VLAN configuration.
If pinging 127.0.0.1 fails on a pc, there is a problem with the local PC, most likely a bad install of TCP/IP.
On a pc the command netstat -rn shows the pcâ€™s routing table.
Additional Telnet commands:
- show sessions shows information about each telnet session, the where command does the same thing.
- resume x, x being the session number is used to resume a telnet session.
- To suspend a session use the command CTRL+ALT+6.
- To disconnect an open session use the command disconnect x, x being the session number.
Ping result codes:
- !!!!! â€“ IP connectivity to the destination is ok.
- â€¦.. â€“ IP connectivity to the destination does not exist.
- U.U.U â€“ the local router has a route to the destination, but a downstream router does not.
debug ip packet â€“ can help troubleshooting the above ping results.
When using traceroute or extended ping the Escape Sequence is: CTRL+SHIFT+6.
Extended ping can only be run from enable mode.
If a routing table contains multiple routes to the same destination with multiple next hops and the prefixes are different, the most specific (longest) prefix route will be used. If all of the prefix lengths are the same the Administrative Distance will be used. [AD/Metric].
Administrative Distance is a measure of a routes believability, with a lower AD being more believable than a route with a higher AD. AD only comes into play if the prefix lengths are the same.
You can set the Administrative Distance on a static route with the command ip route 55.55.55.0 255.255.255.0 192.168.1.2 150, you would do this to set a backup route if a dynamic route fails/is not available in the routing table.

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