Modern networks no longer use classful IP addressing and the subnet mask cannot be determined by the value of the first octet. The classless IPv4 routing protocols (RIPv2, EIGRP, OSPF, and IS-IS) all include the subnet mask information with the network address in routing updates. Classless routing protocols support VLSM and CIDR.
IPv6 routing protocols are classless. The distinction whether a routing protocol is classful or classless typically only applies to IPv4 routing protocols. All IPv6 routing protocols are considered classless because they include the prefix-length with the IPv6 address.
Different Classless Routing Protocols are discussed below -
RIPv2
RIPv2 was first described in RFC 1388 and RFC 1723 (1994); the current RFC is 2453, written in November 1998. Although current environments use advanced routing protocols such as OSPF and EIGRP, there still are networks using RIP. The need to use VLSMs and other requirements prompted the definition of RIPv2.
RIPv2 improves upon RIPv1 with the ability to use VLSM, with support for route authentication, and with multicasting of route updates. RIPv2 supports CIDR. It still sends updates every 30 seconds and retains the 15-hop limit; it also uses triggered updates.
EIGRP
Cisco Systems released EIGRP in the early 1990s as an evolution of IGRP toward a more scalable routing protocol for large internetworks. EIGRP is a classless protocol that permits the use of VLSMs and that supports CIDR for the scalable allocation of IP addresses. EIGRP does not send routing updates periodically, as does IGRP. EIGRP allows for authentication with simple passwords or with MD5. EIGRP AutoSummarises networks at network borders and can load-balance over unequal–cost paths. Packets using EIGRP use IP protocol 88. Only Cisco routers can use EIGRP.
OSPF
The OSPF protocol is a link-state routing protocol, which means that the routers exchange topology information with their nearest neighbours. The topology information is flooded throughout the AS, so that every router within the AS has a complete picture of the topology of the AS. This picture is then used to calculate end-to-end paths through the AS, normally using a variant of the Dijkstra algorithm. Therefore, in a link-state routing protocol, the next hop address to which data is forwarded is determined by choosing the best end-to-end path to the eventual destination.
IS-IS
IS-IS is an IGP, link-state routing protocol, like OSPF. It forms neighbour adjacencies, has areas, exchanges link-state packets, builds a link-state database and runs the Dijkstra SPF algorithm to find the best path to each destination, which is installed in the routing table.
Back when OSPF and IS-IS were developed, IP wasn’t the dominant protocol that it is today. When people think of OSI they automatically think of the OSI-model but back then, ISO (International Organization for Standardization) also created something like IP and UDP called CLNP (Connectionless-mode Network Protocol) and CLNS (Connectionless-mode Network Service).
The Debug Commands used in Configuring routers
a. debug ip http all
To enable debugging output for all HTTP processes on the system, use the debug ip http all command in privileged EXEC mode. To disable debugging output, use the no form of this command.
debug ip http all
no debug ip http all
Syntax Description : This command has no arguments or keywords.
Command Default : Disabled
Command Modes
- Privileged EXEC (#)
- Command History
b. debug ip http authentication
To troubleshoot HTTP authentication problems, use the debug ip http authentication command in privileged EXEC mode. To disable debugging output, use the no form of this command.
debug ip http authentication
no debug ip http authentication
Syntax Description: This command has no arguments or keywords.
Command Modes:
- Privileged EXEC (#)
- Command History
c. debug ip http ezsetup
To display the configuration changes that occur during the EZ Setup process, use the debugip http ezsetup command in privileged EXEC mode. To disable debugging output, use the no form of this command.
debug ip http ezsetup
no debug ip http ezsetup
Syntax Description: This command has no arguments or keywords.
Command Modes:
- Privileged EXEC
d. debug ip http secure-all
To generate the following output, use the debug ip http secure-all command in privileged EXEC mode:
- The debugging information generated by
the debug ip http secure-session command - The debugging information generated by
the debug ip http secure-state command - Debugging information for each call to the SSL driver, for use primarily by Cisco support personnel
To disable this debugging, use the no form of this command.
debug ip http secure-all
no debug ip http secure-all
Syntax Description: This command has no arguments or keywords.
Command Default: Disabled.
Command Modes:
- Privileged EXEC
e. debug ip http secure-session
To generate debugging information about each new secure HTTPS session when it is created, use the debug ip http secure-session command in privileged EXEC mode. To disable this debugging, use the no form of this command.
debug ip http secure-session
no debug ip http secure-session
Syntax Description: This command has no arguments or keywords.
Command Default: Disabled.
Command Modes:
- Privileged EXEC
How to configure a router using Command line Interface (CLI) to change the router to different modes
To aid in the configuration of Cisco devices, the Cisco IOS XE command-line interface is divided into different command modes. Each command mode has its own set of commands available for the configuration, maintenance, and monitoring of router and network operations. The commands available to you at any given time depend on the mode you are in. Entering a question mark (? ) at the system prompt (router prompt) allows you to obtain a list of commands available for each command mode.
The use of specific commands allows you to navigate from one command mode to another. The standard order that a user would access the modes is as follows: user EXEC mode; privileged EXEC mode; global configuration mode; specific configuration modes; configuration submodes; and configuration subsumes.
When you start a session on a router, you generally begin in user EXEC mode, which is one of two access levels of the EXEC mode. For security purposes, only a limited subset of EXEC commands are available in user EXEC mode. This level of access is reserved for tasks that do not change the configuration of the router, such as determining the router status.
In order to have access to all commands, you must enter privileged EXEC mode , which is the second level of access for the EXEC mode. Normally, you must enter a password to enter privileged EXEC mode. In privileged EXEC mode, you can enter any EXEC command, because privileged EXEC mode is a superset of the user EXEC mode commands.
Most EXEC mode commands are one-time commands, such as show or more commands, which show the current configuration status, and clear commands, which clear counters or interfaces. EXEC mode commands are not saved across reboots of the router.
From privileged EXEC mode, you can enter global configuration mode . In this mode, you can enter commands that configure general system characteristics. You also can use global configuration mode to enter specific configuration modes. Configuration modes, including global configuration mode, allow you to make changes to the running configuration. If you later save the configuration, these commands are stored across router reboots.
From global configuration mode you can enter a variety of protocol-specific or feature-specific configuration modes. The CLI hierarchy requires that you enter these specific configuration modes only through global configuration mode. As an example, this chapter describes interface configuration mode, a commonly used configuration mode.
From configuration modes, you can enter configuration submodes. Configuration submodes are used for the configuration of specific features within the scope of a given configuration mode. As an example, this chapter describes the subinterface configuration mode, a submode of the interface configuration mode. ROM monitor mode is a separate mode used when the router cannot boot properly. If your system (router, switch, or access server) does not find a valid system image to load when it is booting, the system will enter ROM monitor mode. ROM monitor (ROMMON) mode can also be accessed by interrupting the boot sequence during startup.