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EspañolCISCO IOS
'Cisco IOS' (originally 'Internetwork Operating System') is the software used on the vast majority of Cisco Systems routers and all current Cisco network switches. IOS is a package of routing, switching, internetworking and telecommunications functions tightly integrated with a multitasking operating system. The first IOS was written by William Yeager.
Cisco IOS has a characteristic command line interface (CLI), whose style has been widely copied by other networking products. The IOS CLI provides a fixed set of multiple-word commands -- the set available is determined by the "mode" and the privilege level of the current user. "Global configuration mode" provides commands to change the system's configuration, and "interface configuration mode" provides commands to change the configuration of a specific interface. All commands are assigned a ''privilege level'', from 0 to 15, and can only be accessed by users with the necessary privilege. Through the CLI, the commands available to each privilege level can be defined.
Cisco IOS versions are versioned using three numbers and some letters, in the general form a.b(c.d)e, where
★ a is the major version number of the release
★ b is the minor version number
★ c is the release number, which begins at one and increments as new releases in the same a.b train are released
★ d (omitted from general releases) is the interim build number
★ e (zero, one or two letters) is the release train identifier, such as none (which designates the mainline, see below), T (for Technology), E (for Enterprise), S (for Service provider), XA as a special functionality train, XB as a different special functionality train etc.
For example, release 12.3(1) is the first mainline Cisco IOS release of version 12.3. 12.3(2) is the next release, and so on. 12.3(1)T is the first release of the T train, 12.3(2)T the next, and so on. Interim builds are candidates for the next release, and are frequently made available by Cisco support as a faster way to provide fixes for bugs before the next release is available. For example, 12.3(1.2)T is the 2nd interim build after release 12.3(1)T.
'Rebuilds' - Often a rebuild is compiled to fix a single specific problem or vulnerability for a given IOS version. For example, 12.1(8)E14 is a Rebuild, the 14 denoting the 14th rebuild of 12.1(8)E. Rebuilds are produced to either quickly repair a defect, or to satisfy customers who do not want to upgrade to a later major revision because they may be running critical infrastructure on their devices, and hence prefer to minimise change and risk.
'Interim releases' - Are usually produced on a weekly basis, and form a roll-up of current development effort. The Cisco advisory web site may list more than one possible interim to fix an associated issue (the reason for this is unknown to the general public).
'Maintenance releases' - Rigorously tested releases that are made available and include enhancements and bug fixes. Cisco recommend upgrading to Maintenance releases where possible, over Interim and Rebuild releases.
Cisco IOS releases are split into several "trains", each containing a different set of features. Trains more or less map onto distinct markets or groups of customers that Cisco is targeting.
★ The 'mainline' train is designed to be the most stable release the company can offer, and its feature set never expands during its lifetime. Updates are released only to address bugs in the product. The previous technology train becomes the source for the current mainline train--for example, the 12.1T train becomes the basis for the 12.2 mainline. Therefore, to determine the features available in a particular mainline release, look at the previous T train release.
★ The 'T' - Technology train, gets new features and bug fixes throughout its life, and is therefore less stable than the mainline. (In releases prior to Cisco IOS Release 12.0, the 'P' train served as the Technology train.)
★ The 'S' - Service Provider train, runs only on the company's core router products and is heavily customized for Service Provider customers.
★ The 'E' - Enterprise train, is customized for implementation in enterprise environments.
★ The 'B' - broadband train, support internet based broadband features.
★ The 'X
★ ' - ''The XA, Xb ... special functionality train, needs to be documented''
There are other trains from time to time, designed for specific needs -- for example, the 12.0AA train contained new code required for Cisco's AS5800 product.
Most Cisco products that run IOS also have one or more "feature sets" or "packages", typically eight packages for Cisco routers and five packages for Cisco switches. For example, Cisco IOS releases meant for use on Catalyst switches are available as "standard" versions (providing only basic IP routing), "enhanced" versions, which provide full IPv4 routing support, and "advanced IP services" versions, which provide the enhanced features as well as IPv6 support.
Each individual package corresponds to one service category, such as
★ IP data
★ Converged voice and data
★ Security and VPN
For additional information about Cisco IOS Packaging see White Paper: Cisco IOS Reference Guide
In all versions of Cisco IOS, packet routing and forwarding (switching) are distinct functions. Routing and other protocols run as Cisco IOS processes and contribute to the Routing Information Base (RIB). This is processed to generate the final IP forwarding table (FIB -- Forwarding Information Base), which is used by the forwarding function of the router. On router platforms with software-only forwarding (e.g. Cisco 7200) most traffic handling, including access control list filtering and forwarding, is done at interrupt level using Cisco Express Forwarding (CEF) or dCEF (Distributed CEF). This means IOS does not have to do a process context switch to forward a packet. Routing functions such as OSPF or BGP4 run at the process level. In routers with hardware-based forwarding, such as the Cisco 12000 series, IOS computes the FIB in software and loads it into the forwarding hardware (such as an ASIC or network processor), which performs the actual packet forwarding function.
Cisco IOS has a "monolithic" architecture, which means that it runs as a single image and all processes share the same memory space. There is no memory protection between processes, which means that bugs in IOS code can potentially corrupt data used by other processes. It also has a "run to completion" scheduler, which means that the kernel does not pre-empt a running process -- the process must make a kernel call before other processes get a chance to run. For Cisco products that required very high availability, such as the Cisco CRS-1, these limitations were not acceptable. In addition, competitive router operating systems that emerged 10-20 years after IOS, such as Juniper's JunOS, were designed not to have these limitations. Cisco's response was to develop a new version of Cisco IOS called IOS-XR that offered modularity and memory protection between processes, lightweight threads, pre-emptive scheduling and the ability to independently re-start failed processes. IOS-XR uses a 3rd party real-time operating system microkernel (QNX), and a large part of the current IOS code was re-written to take advantage of the features offered by the new kernel -- a massive undertaking. But the microkernel architecture removes from the kernel all process that are not absolutely required to run in the kernel, and executes them as processes similar to the application processes. Through this method, IOS-XR is able to achieve the high availability desired for the new router platform. Thus IOS and IOS-XR are very different codebases, though related in functionality and design. In 2005, Cisco introduced IOS-XR on the Cisco 12000 series platform, extending the microkernel architecture from the CRS-1 to Cisco's widely deployed core router.
Recently (in 2006), Cisco has made available IOS Software Modularity which extends the QNX microkernel into a more traditional IOS environment, but still providing the software upgrade capabilities that customers are demanding. It is currently available on the Catalyst 6500 enterprise switch.
To use Cisco IOS Command Line Interface you need to change modes in order to enter different commands. Here is a quick sketch on how to get from mode to mode.
You can tell which mode you are in by the Prompt e.g Router# (Privileged Mode). Here is a table version of how you get from mode to mode.
Global Configuration Mode is the privilege level in Cisco Systems IOS used to configure global router and network switch parameters.
The mode is entered from enable mode using the command "configure terminal", more commonly expressed as "conf t".
From inside this mode, you can enter several types of commands: 'interface' commands to enter Interface Configuration Mode, which allow you to configure physical interfaces, 'line' commands, to configure terminal lines, and 'router' commands to configure routing protocols.
The command
★ Name of Interface
★ IP Address and Subnet mask that have been assigned to that card.
★ Information showing if the card is connected physically to the router.
★ if they have been enabled on the router.
Troubleshooting information for the the Phyiscal and Data Link Layer (OSI) of the router can be viewed by the
The status field indicates the status of interface. Valid values and their meanings are:
★ up—Interface is up.
★ down—Interface is down.
★ administratively down—Interface is administratively down. The Interface was not enabled at setup.
Although rarely seen, The Interface
To use Help, enter the question mark character:
To allow administrators to identify routers they use, they can give the router a name. This can be done by using the command
Each network interface on the router can have it own IP address and Subnet Mask. You can change each individual interface card by typing
syntax is: interface [Name Of Interface] e.g interface FastEthernet0/0, int FastEthernet0/1 etc
The name of the interface refers to the following.
★ Fast Ethernet f0/0 (this allows you to plug in a switch)
★ Fast Ethernet f0/1 (this allows you to plug in another switch)
★ Serial s0/0 (this allows you to plug into another router)
★ Serial s0/1 (this allows you to plug into another router)
★
★ DIFFERENT ROUTERS HAVE DIFFERENT AMOUNTS AND TYPES OF INTERFACES.
★
★
One you have selected a card you can give that card an IP Address and subnet mask
Syntax is: IP address [ip address] [subnet]
For Serial interfaces one card acts as a server and the other acts as the client. On the server machine so that the cards can synchronize messages use the command. To determine if the cable you are using is indeed a DCE cable, you would issue the following command:
By default, when you give a card an IP address and subnet mask the interface is disabled. Use the command
You can shutdown that card by doing the above and use the command
The Router can use the many different routing protocols available such as RIP to inform the router about the presence of other routers and networks.
If you are using RIP, then the following CLI commands are sufficient.
If you want to use RIPv2, you must tell the router this. You can do this by adding the following line to the above code:
Cisco IOS has proven vulnerable to buffer overflows and other problems that have afflicted other operating systems and applications. Cisco usually responds very quickly to all bugs in its maintained software.
A legacy CLI issue, retained for compatibility reasons, is that passwords encrypted on the CLI as 'Type 7' hash values, such as "Router(config)#username jdoe password 7 ''0832585B1910010713181F''", are easily decrypted using software called "getpass" available since 1995; the above example decrypts to "stupidpass". Although this is old news, use of these weak hashes continues due to ignorance of the problem (see Insecure.org Cisco password decryption).However, the program will not decrypt passwords set with the 'enable secret' command. The unexpected concern that this program has caused among Cisco customers has led Cisco to suspect that many customers are relying on Cisco password encryption for more security than it was designed to provide.
Note: Cisco recommends that all Cisco IOS devices implement the authentication, authorization, and accounting (AAA) security model. AAA can use local, RADIUS, and TACACS+ databases.
To display the current routing table stored in DRAM
To telnet into another device
To telnet into another device using hostnames (must have hostnames resolved by DNS or locally)
To display current IOS version, config register, and basic hardware information including CPU and installed devices
To display the current running configuration being used by the router
To display the configuration stored in NVRAM
To ping another device using ICMP echo request
To cause passwords to be obfuscated in the config using basic type 7 encryption (weak protection)
To set a hashed password using the MD5 algorithm
Allow the command you were typing to be generated in a new line, when interrupted by a router state change. This prevents debugging or other information from disrupting your typing, otherwise messages will be printed directly after your typing which can become very annoying.
Perform a router test crash on memory, bus, cpu
★ SAN-OS
★ Network operating system
★ Catalyst switch
★ RANCID (Really Awesome New Cisco confIg Differ)
★ Cisco IOS Software Configuration Guides and Command References (Versions 10.0 through 12.4)
★ Cisco IOS Software Release Reference Guide; comprehensive guide to IOS versioning information
★ Cisco Security Advisories; Complete History
★ Security Configuration Guide
★ Cisco IOS Commands
★ Cisco-centric Open Source Community
★ NMIS - Network Management Information System
★ Cisco IOS commands to prevent flooding/congestion.
★ Cisco 7200/3600 Simulator using IOS Images
★ Cisco Simulator
★ Cisco IOS Packaging
★ Cisco IOS Exploitation Techniques
Cisco IOS has a characteristic command line interface (CLI), whose style has been widely copied by other networking products. The IOS CLI provides a fixed set of multiple-word commands -- the set available is determined by the "mode" and the privilege level of the current user. "Global configuration mode" provides commands to change the system's configuration, and "interface configuration mode" provides commands to change the configuration of a specific interface. All commands are assigned a ''privilege level'', from 0 to 15, and can only be accessed by users with the necessary privilege. Through the CLI, the commands available to each privilege level can be defined.
Versioning
Cisco IOS versions are versioned using three numbers and some letters, in the general form a.b(c.d)e, where
★ a is the major version number of the release
★ b is the minor version number
★ c is the release number, which begins at one and increments as new releases in the same a.b train are released
★ d (omitted from general releases) is the interim build number
★ e (zero, one or two letters) is the release train identifier, such as none (which designates the mainline, see below), T (for Technology), E (for Enterprise), S (for Service provider), XA as a special functionality train, XB as a different special functionality train etc.
For example, release 12.3(1) is the first mainline Cisco IOS release of version 12.3. 12.3(2) is the next release, and so on. 12.3(1)T is the first release of the T train, 12.3(2)T the next, and so on. Interim builds are candidates for the next release, and are frequently made available by Cisco support as a faster way to provide fixes for bugs before the next release is available. For example, 12.3(1.2)T is the 2nd interim build after release 12.3(1)T.
'Rebuilds' - Often a rebuild is compiled to fix a single specific problem or vulnerability for a given IOS version. For example, 12.1(8)E14 is a Rebuild, the 14 denoting the 14th rebuild of 12.1(8)E. Rebuilds are produced to either quickly repair a defect, or to satisfy customers who do not want to upgrade to a later major revision because they may be running critical infrastructure on their devices, and hence prefer to minimise change and risk.
'Interim releases' - Are usually produced on a weekly basis, and form a roll-up of current development effort. The Cisco advisory web site may list more than one possible interim to fix an associated issue (the reason for this is unknown to the general public).
'Maintenance releases' - Rigorously tested releases that are made available and include enhancements and bug fixes. Cisco recommend upgrading to Maintenance releases where possible, over Interim and Rebuild releases.
Trains
Cisco IOS releases are split into several "trains", each containing a different set of features. Trains more or less map onto distinct markets or groups of customers that Cisco is targeting.
★ The 'mainline' train is designed to be the most stable release the company can offer, and its feature set never expands during its lifetime. Updates are released only to address bugs in the product. The previous technology train becomes the source for the current mainline train--for example, the 12.1T train becomes the basis for the 12.2 mainline. Therefore, to determine the features available in a particular mainline release, look at the previous T train release.
★ The 'T' - Technology train, gets new features and bug fixes throughout its life, and is therefore less stable than the mainline. (In releases prior to Cisco IOS Release 12.0, the 'P' train served as the Technology train.)
★ The 'S' - Service Provider train, runs only on the company's core router products and is heavily customized for Service Provider customers.
★ The 'E' - Enterprise train, is customized for implementation in enterprise environments.
★ The 'B' - broadband train, support internet based broadband features.
★ The 'X
★ ' - ''The XA, Xb ... special functionality train, needs to be documented''
There are other trains from time to time, designed for specific needs -- for example, the 12.0AA train contained new code required for Cisco's AS5800 product.
Cisco IOS Packaging or Feature sets
Most Cisco products that run IOS also have one or more "feature sets" or "packages", typically eight packages for Cisco routers and five packages for Cisco switches. For example, Cisco IOS releases meant for use on Catalyst switches are available as "standard" versions (providing only basic IP routing), "enhanced" versions, which provide full IPv4 routing support, and "advanced IP services" versions, which provide the enhanced features as well as IPv6 support.
Each individual package corresponds to one service category, such as
★ IP data
★ Converged voice and data
★ Security and VPN
For additional information about Cisco IOS Packaging see White Paper: Cisco IOS Reference Guide
Architecture
In all versions of Cisco IOS, packet routing and forwarding (switching) are distinct functions. Routing and other protocols run as Cisco IOS processes and contribute to the Routing Information Base (RIB). This is processed to generate the final IP forwarding table (FIB -- Forwarding Information Base), which is used by the forwarding function of the router. On router platforms with software-only forwarding (e.g. Cisco 7200) most traffic handling, including access control list filtering and forwarding, is done at interrupt level using Cisco Express Forwarding (CEF) or dCEF (Distributed CEF). This means IOS does not have to do a process context switch to forward a packet. Routing functions such as OSPF or BGP4 run at the process level. In routers with hardware-based forwarding, such as the Cisco 12000 series, IOS computes the FIB in software and loads it into the forwarding hardware (such as an ASIC or network processor), which performs the actual packet forwarding function.
Cisco IOS has a "monolithic" architecture, which means that it runs as a single image and all processes share the same memory space. There is no memory protection between processes, which means that bugs in IOS code can potentially corrupt data used by other processes. It also has a "run to completion" scheduler, which means that the kernel does not pre-empt a running process -- the process must make a kernel call before other processes get a chance to run. For Cisco products that required very high availability, such as the Cisco CRS-1, these limitations were not acceptable. In addition, competitive router operating systems that emerged 10-20 years after IOS, such as Juniper's JunOS, were designed not to have these limitations. Cisco's response was to develop a new version of Cisco IOS called IOS-XR that offered modularity and memory protection between processes, lightweight threads, pre-emptive scheduling and the ability to independently re-start failed processes. IOS-XR uses a 3rd party real-time operating system microkernel (QNX), and a large part of the current IOS code was re-written to take advantage of the features offered by the new kernel -- a massive undertaking. But the microkernel architecture removes from the kernel all process that are not absolutely required to run in the kernel, and executes them as processes similar to the application processes. Through this method, IOS-XR is able to achieve the high availability desired for the new router platform. Thus IOS and IOS-XR are very different codebases, though related in functionality and design. In 2005, Cisco introduced IOS-XR on the Cisco 12000 series platform, extending the microkernel architecture from the CRS-1 to Cisco's widely deployed core router.
Recently (in 2006), Cisco has made available IOS Software Modularity which extends the QNX microkernel into a more traditional IOS environment, but still providing the software upgrade capabilities that customers are demanding. It is currently available on the Catalyst 6500 enterprise switch.
Cisco Using the Command Line
To use Cisco IOS Command Line Interface you need to change modes in order to enter different commands. Here is a quick sketch on how to get from mode to mode.
An example of Cisco router modes and simple commands
Moving from Mode to Mode
You can tell which mode you are in by the Prompt e.g Router# (Privileged Mode). Here is a table version of how you get from mode to mode.
| Name Of Mode | What You can Do | Prompt | How To Get into this Mode from Previous Mode | How you get back to previous Mode |
|---|---|---|---|---|
| User Exec Mode | Basic show commands, telnet, not very much. | Router> | this is the mode you first start off with | |
| Privileged Mode | You can use the Show command to find out more about the interfaces and routing protocols | Router# | enable | disable, exit |
| Global Configuration Mode | Allows you to change the name of the router | Router(config)# | Router#config t | end, exit, CTRL+Z |
| Interface Mode | Allows you to change the IP Address / Subnet Mask of individual cards on the router | Router(config-if)# | From Global Config Mode use the command int [name of card] | end (takes you back to global config mode), exit |
| Routing Configuration Mode | Allows you to config the routing protocol. This allows you to specify local networks. So other routers attached can find out about the network. | Router(config-router)# | From Global Config Mode use the command router routing-protocol-name | end (takes you back to global config mode), exit |
Global Configuration Mode
Global Configuration Mode is the privilege level in Cisco Systems IOS used to configure global router and network switch parameters.
The mode is entered from enable mode using the command "configure terminal", more commonly expressed as "conf t".
router# configure terminal
router(config)#
From inside this mode, you can enter several types of commands: 'interface' commands to enter Interface Configuration Mode, which allow you to configure physical interfaces, 'line' commands, to configure terminal lines, and 'router' commands to configure routing protocols.
Finding out the status of the Cards
The command
Router#show ip interface brief shows a table of the current interfaces available. The following information is shown.★ Name of Interface
★ IP Address and Subnet mask that have been assigned to that card.
★ Information showing if the card is connected physically to the router.
★ if they have been enabled on the router.
Troubleshooting information for the the Phyiscal and Data Link Layer (OSI) of the router can be viewed by the
Router#show ip interface brief command. The Following is an example of the output of this command:Router# show ip interface brief
Interface IP-Address OK? Method Status Protocol
Ethernet0 10.108.00.5 YES NVRAM down up
Ethernet1 unassigned YES unset administratively down down
Loopback0 10.108.200.5 YES NVRAM down down
Serial0 10.108.100.5 YES NVRAM up up
Serial1 10.108.40.5 YES NVRAM up up
Serial2 10.108.100.5 YES manual up up
Serial3 unassigned YES unset administratively down down
The status field indicates the status of interface. Valid values and their meanings are:
★ up—Interface is up.
★ down—Interface is down.
★ administratively down—Interface is administratively down. The Interface was not enabled at setup.
| Interface | Protocol | Type of error |
|---|---|---|
| UP | UP | Layer 1 and 2 of the OSI Model are operating correctly and the errors are results of higher layers. |
| UP | DOWN | Layer 2 of the OSI Model Error. Items such as protocol error or an encapsulation error. |
| DOWN | DOWN | Layer 1 malfunction, Items such as Cables, Physical Interfaces, Other intermediate devices should be checked for power and correct installation |
| DOWN | UP | Duplicate MAC Address on the LAN connected to the Ethernet interface or a service module error within an internal expansion card |
Although rarely seen, The Interface
Down and Protocol Up error has been known to occur when dealing with faulty expansion cards. Duplicate MAC address have caused the Down / Up display because of a software error in older versions of the CLI.Getting Help in the CLI
To use Help, enter the question mark character:
?. This will print a list of all commands available in the current mode. Changing the Name of The router
To allow administrators to identify routers they use, they can give the router a name. This can be done by using the command
Router>enable
Router#configure terminal
Router(config)#hostname "Name of router"Changing the Interface Card IP Address and Subnet Mask
Each network interface on the router can have it own IP address and Subnet Mask. You can change each individual interface card by typing
Router>enable
Router#config terminal (short for configure terminal)
syntax is: interface [Name Of Interface] e.g interface FastEthernet0/0, int FastEthernet0/1 etc
Router(config)#interface FastEthernet0/0
The name of the interface refers to the following.
★ Fast Ethernet f0/0 (this allows you to plug in a switch)
★ Fast Ethernet f0/1 (this allows you to plug in another switch)
★ Serial s0/0 (this allows you to plug into another router)
★ Serial s0/1 (this allows you to plug into another router)
★
★ DIFFERENT ROUTERS HAVE DIFFERENT AMOUNTS AND TYPES OF INTERFACES.
★
★
One you have selected a card you can give that card an IP Address and subnet mask
Syntax is: IP address [ip address] [subnet]
Router(config-if)#IP address 192.168.20.1 255.255.255.0
For Serial interfaces one card acts as a server and the other acts as the client. On the server machine so that the cards can synchronize messages use the command. To determine if the cable you are using is indeed a DCE cable, you would issue the following command:
Router>show controllers serial <# here>
Router(config-if)#Clock rate 64000By default, when you give a card an IP address and subnet mask the interface is disabled. Use the command
Router(config-if)#no shutdown to bring the system online. You can shutdown that card by doing the above and use the command
Router(config-if)#shutdown.Add Networks to the Router
The Router can use the many different routing protocols available such as RIP to inform the router about the presence of other routers and networks.
If you are using RIP, then the following CLI commands are sufficient.
Router>enable
Router#configure terminal
Router(config)#router rip
Router(config-router)#network [network id]
If you want to use RIPv2, you must tell the router this. You can do this by adding the following line to the above code:
Router(config-router)#version 2Security and vulnerabilities
Cisco IOS has proven vulnerable to buffer overflows and other problems that have afflicted other operating systems and applications. Cisco usually responds very quickly to all bugs in its maintained software.
A legacy CLI issue, retained for compatibility reasons, is that passwords encrypted on the CLI as 'Type 7' hash values, such as "Router(config)#username jdoe password 7 ''0832585B1910010713181F''", are easily decrypted using software called "getpass" available since 1995; the above example decrypts to "stupidpass". Although this is old news, use of these weak hashes continues due to ignorance of the problem (see Insecure.org Cisco password decryption).However, the program will not decrypt passwords set with the 'enable secret' command. The unexpected concern that this program has caused among Cisco customers has led Cisco to suspect that many customers are relying on Cisco password encryption for more security than it was designed to provide.
Note: Cisco recommends that all Cisco IOS devices implement the authentication, authorization, and accounting (AAA) security model. AAA can use local, RADIUS, and TACACS+ databases.
Other useful commands
To display the current routing table stored in DRAM
Router# show ip route
To telnet into another device
Router> telnet <IP address>
To telnet into another device using hostnames (must have hostnames resolved by DNS or locally)
Router> telnet
To display current IOS version, config register, and basic hardware information including CPU and installed devices
Router> show version
To display the current running configuration being used by the router
Router# show running-configuration
To display the configuration stored in NVRAM
Router# show startup-configuration
To ping another device using ICMP echo request
Router> ping <IP address>
To cause passwords to be obfuscated in the config using basic type 7 encryption (weak protection)
Router(config)# service password-encryption
To set a hashed password using the MD5 algorithm
Router(config)# enable secret
Allow the command you were typing to be generated in a new line, when interrupted by a router state change. This prevents debugging or other information from disrupting your typing, otherwise messages will be printed directly after your typing which can become very annoying.
Router(config)# line console 0
Router(config-line)# logging-synchronous
Perform a router test crash on memory, bus, cpu
Router# test crash
See also
★ SAN-OS
★ Network operating system
★ Catalyst switch
★ RANCID (Really Awesome New Cisco confIg Differ)
External links
★ Cisco IOS Software Configuration Guides and Command References (Versions 10.0 through 12.4)
★ Cisco IOS Software Release Reference Guide; comprehensive guide to IOS versioning information
★ Cisco Security Advisories; Complete History
★ Security Configuration Guide
★ Cisco IOS Commands
★ Cisco-centric Open Source Community
★ NMIS - Network Management Information System
★ Cisco IOS commands to prevent flooding/congestion.
★ Cisco 7200/3600 Simulator using IOS Images
★ Cisco Simulator
★ Cisco IOS Packaging
★ Cisco IOS Exploitation Techniques
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psst.. try this: add to faves
