Cisco IOS Download

Cisco IOS (short for Internetwork Operating System) is the software used on a majority of CiscoSystems routers and switches. ... Cisco IOS has uses command line interface (CLI), and provides a fixed set of multiple-word commands. 

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IPv6 link-local addresses

IPv6 link-local addresses | Link-local IPv6 addresses have fewer options for how far they can travel: only in a network segment to which a host is connected. Routers do not send packets intended for a link to other links. Each network interface that has the IPv6 protocol enabled must be assigned a link-local IPv6 address. A host can automatically download its own link IP address, or the address can be manually configured.

Shortcut addresses have the prefix FE80 :: / 10. They are mostly used for automatic address configuration and adjacent searches.

Here is a graphical representation of a link IPv6 address:

IPv6 multicast addresses

IPv6 multicast addresses | Multicast addresses in IPv6 are similar to multicast addresses in IPv4. They are used to communicate with dynamic groupings of hosts, such as all routers in the connection (one for many distributors).

Here is a graphical representation of the IPv6 multicast packet:

Multicast IPv6 address

IPv6 multicast addresses begin with FF00 :: / 8. After the first 8 bits, there are 4 bits representing the flag fields indicating the type of particular multicast addresses. The next 4 bits indicate the size of the IPv6 network for which multicast traffic is intended. Routers use the Scop field to determine if multicast traffic can be forwarded. The remaining 112 bits of the address are the multicast group ID.

Some of the possible range values ​​are:

1 - local interface
2 - left-wing
4 - admin-local
5 - Location Local
8 - organizational local
E - global

For example, the addresses beginning with FF02 :: / 16 are multicast addresses that should be on the local connection.

The following table lists some of the most commonly used local multicast addresses:

IPv6 Global unicast addresses

IPv6 Global unicast addresses | Global IPv6 addresses are similar to public IPv4 addresses. As the name suggests, they are routable on the internet. Currently, the IANA has only assigned 2000 :: / 3 addresses to the global pool.

A global IPv6 address consists of two parts:

Subnet ID - 64 bits long. Contains the site's prefix (obtained from a regional Internet registration database) and the subnet (subnet on the site).
Interface ID - 64 bit long. typically from a part of the interface's MAC address.


Here is a graphical representation of the two parts of a global IPv6 address:

IPv6 address format

Unlike IPv4, which uses a decimal point format for every byte interval from 0 to 255, IPv6 uses eight groups of four hexadecimal digits separated by columns. For example, this is a valid IPv6 address:

2340: 0023: AABA: 0A01: 0055: 5054: 9ABC: ABB0

If you do not know how to convert hexadecimal numbers to binary values, here is a table to help you with the conversion:

IPv6 address abbreviation

The above IPv6 address looks scary, right? Well, there are two conventions that can help you shorten the code to write for an IP address:

1. A leading zero can be omitted

For example, the above address (2340: 0023: AABA: 001: 0055: 5054: 9ABC: ABB0) can be abbreviated to 2340: 23: AABA: A01: 55: 5054: 9ABC: ABB0 :.

2. Consecutive fields with zeros can be represented as two colons (: :).

For example, 2340: 0000: 0000: 0455: 0000: AAAB: 1121 may be written as 2340 :: 0455: 0000: AAAB: 1121

NOTE

You can shorten an address only for such an event. The reason is obvious - if you more than doubled the colon, you would not know how many nulls were left out in each part.


Here are some examples to help you understand the concept of IPv6 address truncation:

Long version: 1454: 0045: 0000: 0000: 4140: 0141: 0055: ABBB
Abstract: 1454: 45 :: 4140: 141: 55: ABBB

Long version: 0000: 0000: 0001: AAAA: BBBC: A222: BBBA: 0001
Abstract: :: 1: AAAA: BBBC: A222: BBBA: 1

IPv6 unicast addresses

IPv6 unicast addresses | Unicast addresses represent a single interface. Packets addressed to a unicast address are sent to a specific network interface.

There are three types of IPv6 unicast addresses:

Global unicast - comparable to public IPv4 IP addresses. These addresses are assigned by IANA and used in public networks. You have a prefix of 2000 :: / 3 (all addresses begin with binary 001).
unique local - resembles private IPv4 addresses. They are used in private networks and cannot be routed on the internet. These addresses have the prefix FD00 :: / 8.

Local link - These addresses are used to send packets over the local subnet. Routers do not send packets with this address to other subnets. For IPv6, each network interface that the IPv6 protocol is enabled must be assigned a link-local address. These addresses have the prefix FE80 :: / 10.

More about IPv6 Here:Click here

Types of IPv6 addresses

Unicast - represents a single interface. Packets addressed to a unicast address are sent to a single interface.

Anycast - identifies one or more interfaces. For example, servers that support the same function can use the same unicast IP address. Packets sent to this IP address will be forwarded to the next server. Anycast addresses are used for load balancing. Known as "nearest address".

Multicast - represents a dynamic group of hosts. Packets sent to this address are delivered to many interfaces. Multicast addresses in IPv6 have the same purpose as their counterparts in IPv4.

EIGRP Interview Questions

Debug command

The troubleshooting command displays information about Cisco device operations, traffic generated or received, and any error messages. The information is provided in real time until the user disables debugging or the device restarts.

The debugging operation requires a large amount of CPU resources and should not be used frequently in production environments. It is intended to be used as a debugging tool for a short period of time. You can choose to debug only specific events, such as EIGRP information, received ICMP messages, etc.

Consider the following example:

R1 # debug ip icmp
ICMP packet debugging is enabled
R1 #
R1 #
ICMP: echo response sent, src 10.0.0.2, dst 10.0.0.1

ICMP: echo response sent, src 10.0.0.2, dst 10.0.0.1

In the previous example, you can see that I have enabled debugging only for ICMP events (such as pings). At the output you can see that R1 has responded to the device with the IP address of 10.0.0.1 with two ping response packets.

To disable ICMP event debugging, just type the command with the keyword "no" in front of it:

R1 # no troubleshooting ip icmp
ICMP packet debugging is disabled

To troubleshoot only the RIP messages, we would perform the following command:

R1 # debug ip rip
RIP protocol troubleshooting is enabled
R1 #
R1 # RIP: update v2 was received at 10.0.0.1 on GigabitEthernet0 / 0
172.16.0.0-16 to 0.0.0.0 in 2 jumps
192.168.5.0/24 to 0.0.0.0 in 1 jump
The RIP: v2 update was received at 10.0.0.1 on GigabitEthernet0 / 0
172.16.0.0-16 to 0.0.0.0 in 16 jumps
192.168.5.0/24 to 0.0.0.0 in 16 jumps

You can enable debugging of everything that happens on your device by executing the debug all command (don't use the command on production units because it can produce a large number of results and block the device!)

Remove all command example

To disable this command, type the undebug all command (or all one shortcut).