Sunday, January 20, 2019

Traceroute command

The traceroute command on a Cisco device can be used to identify the path through which a packet reaches its destination. It identifies all routers in the path from the source host to the destination host and can be helpful in troubleshooting network problems. Use this command to find out which router in the path to an unreachable destination should be examined in more detail than the probable cause of the network outage.

In the picture above we can see that we have a network of four routers. The network is working properly. Consider what happens if we issue the traceroute command to R1 to the IP address of the router's R4 Gi0 / 0 interface (
Rl # traceroute
Enter the escape sequence to cancel the operation.

Follow the route to
1 0 ms 0 ms 0 ms
2 0 ms 0 ms 0 ms
3 0 ms 0 ms 0 ms
You can see that the Traceroute command listed the IP addresses of all routers in the path to the destination. Now suppose that the router R3 fails. Now think about the command set:
Rl # traceroute
Enter the escape sequence to cancel the operation.

Follow the route to
1 0 ms 0 ms 0 ms
2! H *! H
3 * *
Note that there is no response from R3 ( With the help of this information we can assume that there is a problem with R3 and investigate the problem. H! The output indicates that the values ​​can not be accessed. Another character that can be displayed in the output command of traceroute is:
Number of milliseconds - round trip time in milliseconds.
* - The probe has taken out
A - Forbidden under administrative law (eg with an access list).
Q Source off (target is too busy).
The user has interrupted the test.
The U-port is not accessible.
The N network is unreachable.

The P-protocol is not reachable.
T -timeout.

 Unknown package type.

Friday, January 18, 2019

Extended ping command

The Ping command in Cisco IOS (and other operating systems) is used to test the availability of devices on a TCP / IP network. Cisco devices also support the advanced ping command, which makes it possible to more closely examine the host's availability and network connectivity. With this command, you can define the source IP address as any IP address on the router, the number and size of the ping packets, different time intervals, and so on.

The expanded ping command is invoked from privileged exec mode by typing ping and pressing Enter. The following arguments can be changed:

Protocol [ip] - Enter the protocol, such as appletalk, clns, ip, short story, apollo, vines, decnet or xns. The default value is ip.
Destination IP Address - Enter the IP address or host name of the host to which ping is to be sent.
Repeat Numbers - Enter the number of ping packets sent to the destination address. 5 by default.

Datagram size - Enter the size of the ping package (in bytes). The default value is 100 bytes.
Timeout in seconds - Enter time intervals. The default value is 2 seconds. The echo response must be received before the time limit expires for ping to succeed.

Advanced Commands - Specify whether to display a series of additional commands. The default value is no. If you specify Yes, additional arguments are displayed.

Source address or interface: Enter the router's interface or IP address to use as source address for ping packets.

Type of service - Indicates the type of service (ToS). This is the quality choice for the internet service. The default value is 0.

Set DF bit in IP header? - Specify whether to set the Do not Fragment (DF) bit for the ping package. If specified, the No fragment option does not allow for fragmentation of the package. The default is no.

Confirm reply data? - Specify whether response data should be checked. The default is no.
Data Pattern - Enter the data pattern. Data patterns are used to fix framing errors and clock problems on serial lines. The default value is [0xABCD].
Loose, Strict, Record, Timestamp, Verbose - Enter the main IP options.

Sweep Size Range - Specify the size of the sent ping eco packages. This parameter is used to determine the minimum sizes of MTUs configured on the node along the way to the destination address. The default is no.

Thursday, January 17, 2019

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. 

Click Here Download:Cisco IOS 

Tuesday, January 15, 2019

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:

Monday, January 14, 2019

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:

Sunday, January 13, 2019

IPv6 Global unicast addresses

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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:

Saturday, January 12, 2019

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


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

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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

Wednesday, January 9, 2019

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.