Month: January 2013

Wildcard mask – What’s the difference from subnet mask?

What is Wildcard Masking?

Wildcard mask is like any other computer IP address basically a group od zeroes and ones (o and 1). To be short, in wildcard mask all number one (1) mean “I don’t care about that position”, and all zeroes (0) mean “I care about that position in binary address”. Let’s take an example where Access list with wildcardmask will be able to deny fourth subnet and alow next four and so on for all /24 subnets of supernetwork.

In the access-list we put an network;

We know that 255 means 1111 1111 in binary.
We know that 251 means 1111 1011 in binary.

In the line we could change to any other kind of because in this situation our ACL will not care about the bits in the first, second and last octet. We could write it will fit in our example.

One more thing to make myself more clear. If we use deny in ACL, this ACL will not filter only network, but every network in the whole 32bit range from to in which third octet has an zero (0) in 6th position. To filter only those subnets that are part of supernet we would need to use deny because in that way we will say that we care about first and second octet of the address.


| Continue Reading.. |

When I connect to device with telnet or SSH I don’t see logging?

Cisco device will not send log messages to your terminal session by default. That means that you will see log messages in putty only if you are connected to console port but if you connect with telnet or SSH you will not get log messages. Here’s how to resolve this:

There are three types of logging: Console, Monitor and Buffer.
Console logging is seen if you connect to console port directly. Monitor logging is what you will se on your screen when you are connected to CLi in some other way. And the last is Buffer logging that means all the logs that are going into buffer memory to be viewed later in time. Every of the logging type has its own setting on which loggs will be registered.
There are this types of looging levels with their severity numbers where greather number means smaller severity case, from severity 1 to 7:

| Continue Reading.. |

IPv6 – SLAAC EUI-64 Address Format

UPDATE on 22 Mar 2018:
Article is correctly describing what is SLAAC and why is needed and describes how SLAAC uses RFC 2373 to generate interface IPv6 address. The thing is that today RFC 7217 describes an enhanced new way of SLAAC algorithm to improve user security and protect hosts from attacks. Details are available here in my new article about SLAAC.

Stateless autoconfiguration or SLAAC

SLAAC is a method in which the host or router interface is assigned a 64-bit prefix, and then the last 64 bits of its address are derived by the host or router with help of EUI-64 process which is described in next few lines. SLAAC uses NDP protocol to work.ipv6

As the format of the EUI-64 format is seen quite frequently, covering its details seems important too.

| Continue Reading.. |

L2TP – Layer 2 Tunneling Protocol

L2TP Attributes Summary

L2TP tunnelProjected L2TP standard was made available in the year 1999 by means of RFC 2661. It was originated primarily from two different tunneling protocols, named as: Point-to-Point communication protocol and PPTP (Point to Point Tunneling protocol). In other words, L2TP (Layer 2 Tunnel Protocol) is an up-and-coming IETF (Internet Engineering Task Force) standard that came in front with the traits of two on-hand tunneling protocols, named as: Cisco’s L2F  (Layer 2 Forwarding) and Microsoft’s PPTP (Point-to-Point Tunneling Protocol). L2TP protocol is actually an expanded form of the PPP (a significant constituent for VPNs).

| Continue Reading.. |