OSPF metric

•OSPF uses a Metric of  cost=100,000,000/bandwidth(Kbps)

•The default reference bandwdith is 100,000,000 and it  can be changed.

OSPF router type

•We have these types of routers:

–Internal router: All networks (interfaces) connected directly to this router belong to the same area. An internal-router has a single link-state database

–Area Border router: ABR: He has at least 2 connected networks (interfaces) that are in two different areas. ABR will have more than one link-state database, 1 for each area. Its responsibility to exchange topology information between areas

–Backbone router: at least one connected network in area 0 ( can be internal or ABR)

–Autnomous System Boundary router: ASBR: at least one network participating in OSPF, and one network in another routing domain. Its role is to exchange information between OSPF and external routes.

Troubleshooting VTP

•If a switch doesn’t seem to be receiving updated information from a VTP server:

–Either the swtich is in transparent mode. Verify by “show vtp status”

–“there might not be a switch configured as vtp server”

–The link between the switch and the other switches is not in trunking mode. VTP can be advertised only over trunk links. To verify if an interface is trunk or acess

•“show interface type mod/num switchport”

–Make sure the vtp version is compatible with other switches in the VTP domain.

–Make sure the VTP password matches in the vtp domain

–Make sure the VTP domain name match that of the VTP server

VTP configuration

•By default vtp mode is server, management domain is NULL, and there is no password.

•If a switch receives a VTP summary advertisement on a trunk port from any other switch, it will automatically learn the VTP domain name, VLANs and the configuration revision number it hears.

•Before you add a switch to the network, verify that the revision number is set to 0 “show vtp status”

•There is two ways to configure VTP:

–Global config mode

–vlan database mode mostly deprecated

To join a specific VTP management domain, you have to “vtp domain domain-name

Configuring the VTP mode:

–Server mode: multiple VTP servers can coexist in a domain. The servers do not elect primary or secondary, if one server is configured with a new VLAN or VTP parameter, it advertises the changes to the rest of the domain. All other servers synchronize the VTP databases to this advertisement just as any VTP client would

–Client mode: if you want to configure a as VTP server, you start it as a client to learn the latest changes, than you configure it in server mode.

–Transparent mode: this mode is used if a switch will not share the VLAN information with any other switch in the network. VLAN can still be created, deleted or modified, but they are not advertised, however VTP advertisement received by a transparent switch are forwarded out trunk links. Keeping switches in transparent mode can eliminate the chance for duplicate over-lapping VLANs in large network with many network administrators

–“vtp mode {server | client | transparent}

–Vtp password password

On some IOS, you can turn vtp off, by using the command vtp off command. This command allows the switch to act the same as if it is in a vtp transparent with the addition that the switch doesn't forward vtp advertisement on trunk links.
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• http://www.ftp.services

How to configure PPP authentication

I would like to explain in this article how to configure PPP authentication between two routers.
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Let's take a look first at our diagram:

As you see in the image, we have 2 routers connected through serial point-to-point interfaces. The subnet is 192.168.13.0/24.

R3 must authenticate R1, means in order for router R3 to accept PPP connection with router R1, R1 must proove his identity to router R3. And let's say that Router R3 will authenticate R1 by PAP authentication

Let us start with first basic ppp connectivity

Router R3
sh run int s0/0/1
interface Serial0/0/1
ip address 192.168.13.3 255.255.255.0
encapsulation ppp
end

router R1
show run int s0/1/0
interface Serial0/1/0
ip address 192.168.13.1 255.255.255.0
encapsulation ppp
clock rate 2000000
end

So as we said the authentication is PAP, and it is local (means when R3 wants to authenticate router R1, R3 will look in its own local database). So for that purpose, we will create a local username and password on router R3. We will name the user R1User and password is password.
R3(config)#username R1User privilege 1 password password
Now On router R3, we need to tell the router R3 to use local database for ppp authentication.
so first:
R3(config)#aaa new-model
Then we created a list called R1-PPP-AUTH, this list is local authentication list for ppp connectivity
R3(config)#aaa authentication ppp R1-PPP-AUTH local
So now let us attach this list authentication to the ppp connection on the serial interface s0/0/
R3(config-if)#ppp authentication pap R1-PPP-AUTH
R3(config-if)#
%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0/1, changed state to down
R3(config-if)#
As you see that once we configured the ppp authentication, the line protocol goes down on s0/0/1

So what we have to do now is to move the router R1 and configure it to send username and password to router R3, so that router R3 will know that the connection is sent from router R1
R1(config-if)#ppp pap sent-username R1User password password
R1(config-if)#
*Jan 14 10:52:36.919: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/1/0
As you see, once we entered this command on router1, the ppp connection came up.

For PPP CHAP authentication, I will explain it in my ne

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You can also follow our DHCP services and ip services solutions on https://dhcpservices.blogspot.com

I hope this was helpful, and I would like to thank you for reading

5 interview questions for a system administrator

I would like to write a series of questions that can be asked in for a sysadmin position.
First, I would like to introduce myself. My name is anthony, and I am from the team of www.find1job.com. If you are looking for an IT job don't hesitate to post an announce and submit your CV with us http://www.find1job.com/postad/employee/postadv.html


Linux Questions:

How to create a symbolic link ?
ln -s

How to reset a password for a CentOS operating system ?

Boot with the CentOS CD,
Then run ls /dev/sda* to get a list of the drives
mount them, then try to see which one is the / drive (it should contains the /etc directory). change to this drive with chroot, then run passwd command

Windows questions:
How to clean the active directory from a domain controller that had a hardware failure ?
First, if it has one of the 5 roles, I have to seize the roles with another domain controller, then I have to use the ntdsutil command line to remove the failed domain controller form the active directory.

How do I use a domain local group and global group ?
Global group should be related to departments or team. For example, i create a global group for accountants, i create a global group from system admin, another global group for database admin.
Domain local group can be used to assign permissions to ressource (Files,Folders and printers..)
So I assign permission to domain local group (maybe 1 for read only and 1 for read and write), then I add the global group that need access to the specific resource inside that domain local group

 Exchange Server 2010
How to clear the transaction log files for a specific database ?
Backup this datbase

If you are looking for a job as system administrator, or a network administrator. If you are searching a job in IT field. We invite you to post an announce in our recruitment website. It is a totally free website . Our website is not only free for employees, but it is also free for employers. http://www.find1job.com/postannounce.html

I hope this was helpful and I would to thank you for reading.

Get Calendar permissions in Exchange 2010

If you need to give access to a mailbox for a certain user. You can through the Exchange management console give him full access.
How about if you need to give him only a read access to the calendar.
By default everybody in the organization has read free/busy time for the calendar of any mailbox in the organization. How about if you need to give a manager to be able to know what are the meeting, appointments for his employees. You need to give him Reviewer permission on the calendar of his employees.
You cannot do this in Exchange management console, you need to do it in Exchange management shell.
Add-MailboxFolderPermission -Identity "Employee1:\Calendar" -User Manager1 -AccessRights Reviewer

If you are looking for a job as System Analyst, i invite you to post your CV in the website below:
https://www.security-architecture.com/add-cv/

Thanks