Computer Certification

To pass the Cisco CCNA and CCNP certification exams
as well as becoming a world-class networker
you've got to know how and when to use floating static routes. And if you're wondering what makes them "float" -- read on!

In this example
R1 and R2 are running OSPF over a Frame Relay network
172.12
/24. They're also connected by a BRI ISDN link
172.12
/24. R1 is advertising a loopback network
1.1
/32
via OSPF. We want R2 to have a route to that loopback even if the frame goes down - and here
we'll use a floating static route to make that happen.

R2 sees the route to the loopback interface via OSPF
and can ping that interface successfully.

R2#show ip route ospf

1.0.0.0/32 is subnetted
1
subnets

O 1.1.1.1 [110/65] via 172.12.123.1
0
Serial0


R2#ping 1.1.1.1

Type escape sequence to abort.

Sending 5
100
ICMP Echos to 1.1.1.1
timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5)
round-trip min/avg/max = 68/68/68 ms

This is when it's important to know your administrative distances.... or at least know where to look to see them! The AD of OSPF is 110
which means we can configure a static route to 1.1.1.1 /32
and as long as the AD of the static route is higher than 110
it won't be used unless the OSPF route leaves the routing table. That's why this kind of route is called a "floating" static route - the route "floats" in the routing table and isn't seen unless the primary route leaves the table.

You learned how to write a static route in your CCNA studies
but you also remember that the default AD of a static route is either 1 or 0... and both of those values are less than 110! To change the AD of a static route
configure the desired distance at the end of the ip route command.

R2(config)#ip route 1.1.1.1 255.255.255.255 bri0 ?

<1-255> Distance metric for this route

A.B.C.D Forwarding router's address

name Specify name of the next hop

permanent permanent route

tag Set tag for this route


R2(config)#ip route 1.1.1.1 255.255.255.255 bri0 111

The static route has an AD that's only one higher than that of the OSPF route
but that's enough to make the route "float" and not yet be seen in the routing table.

R2#show ip route

1.0.0.0/32 is subnetted
1
subnets

O 1.1.1.1 [110/65] via 172.12.123.1
0
Serial0

172.12.0.0/24 is subnetted
2
subnets

C 172.12.12.0 is directly connected
BRI0

C 172.12.123.0 is directly connected
Serial0

Let's see the effect on the routing table when the Serial0 interface is closed.

R2(config)#int s0

R2(config-if)#shutdown


12:04:53: %OSPF-5-ADJCHG: Process 1
Nbr 172.12.123.1 on Serial0 from FULL to DOWN
Neighbor Down: Interface down or detached


12:04:55: %SYS-5-CONFIG_I: Configured from console by console

12:04:55: %LINK-5-CHANGED: Interface Serial0
changed state to administratively down


12:04:56: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0
changed state to down


R2#show ip route

1.0.0.0/32 is subnetted
1
subnets

S 1.1.1.1 is directly connected
BRI0

172.12.0.0/24 is subnetted
1
subnets

C 172.12.12.0 is directly connected
BRI0

The floating static route appears in the table
but the ISDN link will not come up until the BRI interface has traffic to send. Let's ping 1.1.1.1 and see what happens. debug dialer was configured on R2 before sending the ping.

R2#ping 1.1.1.1

Type escape sequence to abort.

Sending 5
100
ICMP Echos to 1.1.1.1
timeout is 2 seconds:

12:16:01: BR0 DDR: Dialing cause ip (s=172.12.12.2
d=1.1.1.1)

12:16:01: BR0 DDR: Attempting to dial 8358661

12:16:01: %LINK-3-UPDOWN: Interface BRI0:1
changed state to up.!!

12:16:01: BR0:1 DDR: dialer protocol up!!

Success rate is 80 percent (4/5)
round-trip min/avg/max = 36/37/40 ms

The link comes up and traffic can still reach 1.1.1.1. Once R2 becomes an OSPF neighbor of R1 again
the OSPF route will again become the primary path and the floating static route leaves the routing table.

R2(config)#int s0

R2(config-if)#no shut

R2#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

172.12.123.1 1 FULL/DR 00:01:57 172.12.123.1 Serial0


R2#show ip route

1.0.0.0/32 is subnetted
1
subnets

O 1.1.1.1 [110/65] via 172.12.123.1
0
Serial0

172.12.0.0/24 is subnetted
2
subnets

C 172.12.12.0 is directly connected
BRI0

C 172.12.123.0 is directly connected
Serial0

A floating static route is an excellent "back door" that will keep the ISDN link down while allowing that link to serve as a backup route. Just make sure the ISDN link comes down when you expect it to - always check that with show isdn status!

I was reading The Big Moo: Stop Trying To Be Perfect and Start Being Remarkable this morning
and I’d recommend a copy of this to anyone who wants to improve their career and their future. And that’s all of us
right?


There was one particular line that really stood out to me: Betting on change is always the safest bet available. That describes life perfectly
but it also describes a career in Information Technology perfectly as well. There is no field in the world that has the constant and never-ending changes that IT does. And every single one of us can look at this as a massive opportunity for personal and professional growth.


Is that how you’re looking at it? I remember when I passed my first certification exam
the Novell CAN
back in 1997. Man
I thought I knew it all then! But I quickly learned that you’ve got to keep learning in IT. I also learned that if you’re willing to put in the work and make the sacrifices
there’s no other field with the limitless potential for growth and excellence.


Like everyone else
my career has had its ups and downs
but I always kept learning and growing. Today
I’ve got my dream job
working with studI was reading The Big Moo: Stop Trying To Be Perfect and Start Being Remarkable this morning
and I’d recommend a copy of this to anyone who wants to improve their career and their future. And that’s all of us
right?


There was one particular line that really stood out to me: Betting on change is always the safest bet available. That describes life perfectly
but it also describes a career in Information Technology perfectly as well. There is no field in the world that has the constant and never-ending changes that IT does. And every single one of us can look at this as a massive opportunity for personal and professional growth.


Is that how you’re looking at it? I remember when I passed my first certification exam
the Novell CAN
back in 1997. Man
I thought I knew it all then! But I quickly learned that you’ve got to keep learning in IT. I also learned that if you’re willing to put in the work and make the sacrifices
there’s no other field with the limitless potential for growth and excellence.


Like everyone else
my career has had its ups and downs
but I always kept learning and growing. Today
I’ve got my dream job
working with students and customers just like you – to help you create your own future.


The next 18 months are filled with endless possibilities
particularly with the rapid growth of VoIP and Microsoft Vista on the horizon. There will be those who rationalize their inertia
saying “I’ll never have to support those
so I don’t need to learn them."


There will also be those who see VoIP and Vista as enormous opportunities to learn and advance in their careers and their lives. These people will get started today
learning the fundamentals of Cisco and advancing their networking knowledge in order to be ready for opportunities as they come along.


You can’t start studying and learning when the opportunity arrives – you’ve got to be ready when opportunity knocks. If you’ve been putting off studying for a Cisco or other computer certification – and I know the summer is a really good time for putting off studying – get back on track today.


Because you never know what opportunities are going to come along – but you do know that when they do
you’ve got to be ready to take advantage. After all
opportunity really does knock only once!
ents and customers just like you – to help you create your own future.


The next 18 months are filled with endless possibilities
particularly with the rapid growth of VoIP and Microsoft Vista on the horizon. There will be those who rationalize their inertia
saying “I’ll never have to support those
so I don’t need to learn them."


There will also be those who see VoIP and Vista as enormous opportunities to learn and advance in their careers and their lives. These people will get started today
learning the fundamentals of Cisco and advancing their networking knowledge in order to be ready for opportunities as they come along.


You can’t start studying and learning when the opportunity arrives – you’ve got to be ready when opportunity knocks. If you’ve been putting off studying for a Cisco or other computer certification – and I know the summer is a really good time for putting off studying – get back on track today.


Because you never know what opportunities are going to come along – but you do know that when they do
you’ve got to be ready to take advantage. After all
opportunity really does knock only once!

Planning for success on the CCNA
CCNP
and other Cisco exams is much like taking a trip in your car. You've got to plan ahead
accept the occasional detour
and just keep on going until you get there. But what do you do before you get started?

Create a road map - for success.

If you were driving from one side of the country to another
you certainly wouldn't just get in your car and start driving
would you? No. You would plan the trip out ahead of time. What would happen if you just got in the car and started driving in the hope that you would someday arrive at your final destination? You would never get there
and you'd spend a lot of time wandering aimlessly.

Don't spend your study time and slow your progress by studying for a Cisco exam without planning the trip. Schedule your study time as you would an appointment with a client
and keep that appointment. Make sure that your study time is quality study - turn your TV
iPod
and cell off. If you hit a bump in the road and don't get your certification the first time you take the exam
regroup and create another plan. Study until you get to the point that on exam day
you know that you are already a CCNA or CCNP and you’re just there at the testing center to make it official.

The journey to success is not a straight line. When you look at a chart that shows a company's financial progress
the line never goes straight up. there are some ups and downs
but the overall result is success. The path to your eventual career and certification exam success may not be a direct one
but the important part is to get started - and to get any journey started
you've got to create a road map for a successful arrival at your destination.

* What kinds of certifications should I consider for a PC Specialist career?

As a PC Specialist
people will rely on your specialized computer training and skills to keep the office running smoothly. You must have the following certifications:

• PC Specialist Certificate
• Microsoft Certified Systems Engineer
• Microsoft Certified Professional

* What kinds of certifications should I consider for a Software Engineer career?

The software engineer designs and develops systems to control and automate manufacturing
business
or management processes. To obtain a position as a Software Engineer
you must have:

• A four-year degree in a computer-related discipline is required for most software engineering positions.

• Certification in various software applications is suggested.

• Training programs are available at community colleges
vocational schools
technical institutes and in the Armed Forces.

Earning and maintaining computer certification is a good way for software engineers to keep their skills up to date. In addition to Microsoft
Novell
Cisco and other high-tech companies
the Institute of Electrical and Electronics Engineers (IEEE) Computer Society offers relevant computer certifications.

* What kinds of certifications should I consider for a Systems Analyst career?

These workers figure out how to use computers to get things done. They tell businesses and other organizations which computers and software to buy
and they decide how to get those tools to work together. To qualify on this position
you must have:

• A four-year college degree in computer science
information science
or management information systems.

• Microsoft Certification and Microsoft Certified Professional (MCP)

* What kinds of certifications should I consider for a Systems Engineer career?

Systems engineering is like putting together a puzzle
matching varied pieces together to make one cohesive whole. Here are some certifications you need to comply:

• BS in systems engineering or other related engineering discipline or an equivalent combination of education and work related experience.

• Novell certifications

Earning computer certification at a prestigious educational institution is impressive. But
if you don't have that kind of money
you may take computer certification training courses anywhere and anyway you wish and then pay to take the exams. Passing the exams is what earns computer certification.

* What kinds of certifications should I consider for a Technical Instructor career?

As a technical instructor
you need to be mature and very oriented towards people. To be considered
you must have the following certifications:

• A four-year degree in a computer-related discipline is required for most software engineering positions.

• CompTIA’s Certified Technical Trainer (CTT+) certification.

* What kinds of certifications should I consider for a Wireless Specialist career?

Career certification programs are critical for aspiring Wireless Specialists. Many are looking for programs that have a complete engineering curriculum that concentrates entirely on wireless application. Some of these are the following:

• Certified Wireless Professional includes application for wireless development
its networking elements and security
and embedded systems. Number of hours needed to complete the certification depends on the institution offering the program
but in most cases these certifications requires minimum of 200 hours lecture in class room and an average of 200 hours in laboratory practice.

• Cisco Security Professional Design Certifications merely concentrates on the perimeter security of the data in the web site
largely to avoid being hacked. Different versions of Web security courses such as DVS 1.0 and DPS 1.0 are available for reference.

* What does certified mean?

There are four accepted meanings of the adjective “certified” but only two of which satisfy the needed meaning. To be certified means to be endorsed with authority by an institution or a person with higher position after one successfully meets certain requirements. Another meaning is that a person is qualified to do a certain job as supported by an appropriate document better known and regarded as a Certification.


* What certifications are there?

If you are pertaining to online certifications
there are lots to be traced. To help you find one best certification that fits your ability and interest
you may log on to reliable sites in the internet. For now
the following are the basic IT certifications:

• IT Auditing
• Document Imaging
• E-Commerce
• Internet/Intranet
• Linux
• Networking
• Printing
• Project Management
• IT Security
• Servers
• Service Technician
• Technical Trainer
• Webmaster


* Who benefits from certification?

Primarily the one given a certification benefits more. Being certified means one can properly function on a certain job. This means
companies will easily hire a person with certification especially when certifications come from a reliable learning institution.

In some ways
the company to which a certified person intends to apply for work will also benefit since the performance of the applying employee is being supported with a certification.


* Is certification better than experience?

The answer for that is a big "No." Certification means training. It is impossible for a person to send himself training without experiencing what it is he intends to do. For this reason
we cannot equate certification from experience since they do not share the same purpose. However
if you already have work experience
a certification is a big help for promotion
recognition and pay raises.

On the other hand
companies are not solely after experience but after educational attainments and performances. In other words
having completed a course as proved by a certification is a chance to be hired.


* Which certification program is best for me?

The best certification program for you is the one that fits your interests and capabilities. Those two factors should be considered above all ese when finding the right and best certification program for you.


* How much will getting certified cost?

Almost all training packages from different training institutions are cost effective. The training cost will depend on the training you want to pursue and in which training institution you intend to enroll. Generally
a trainee should prepare to pay between $100 and $400 for each training program.


* How long will certification take?

There are training institutions that offer a 6-month online training program. The usual training timeframe is one year. This length of training may exceed to a maximum of 2 years depending on the program conducted.


* Do I need a college degree to be certified?

You do not need a college degree to be certified. Some certification programs require one to have at least finished high school upon enrolling in a certain course.


* Will certification really help my career?

A certification may help your career. Nowadays
competition in the jobs is getting tougher. For one to stay in his or her job or to be promoted to a higher position
one factor to consider is his or her educational achievements. That is one reason why mastering your field of work by means of studying and training can be a great boost for your career. That is where a certification program can make or break your career advancement.


* Will I have to go somewhere for my certification training?

While you can find local institutions where you can take classes and tests
most training is done online now. You do not need to go somewhere else for your training. You do not even need to attend classes personally for your lessons. Not only is training done mostly online now
but examinations for certification are also given online.

Like TCP
BGP is connection-oriented. An underlying connection between two BGP speakers is established before any routing information is exchanged. This connection takes place on TCP port 179. As with EIGRP and OSPF
keepalive messages are sent out by the BGP speakers in order to keep this relationship alive.

Once the connection is established
the BGP speakers exchange routes and synchronize their tables. After this initial exchange
a BGP speaker will only send further updates upon a change in the network topology.

The IGP protocols that use Autonomous Systems
IGRP and EIGRP
require prospective neighbors to be in the same AS. This is not true with BGP. Routers can be in different Autonomous Systems and still exchange routes. The BGP neighbors do not have to be directly connected
and often are not
but do need to be able to reach the IP addresses they use in their neighbor statements.

A BGP peer that is in the same AS is referred to as an Internal BGP (iBGP) Peer
where a BGP peer in another AS is an External BGP (eBGP) Peer.

A sample iBGP configuration:

Router bgp 100

Neighbor 10.1.1.2 remote-as 100


A sample eBGP configuration:

Router bgp 100

Neighbor 10.1.1.2 remote-as 200

Cisco recommends that eBGP peers be directly connected
where iBGP peers generally will not be.

Before we get too much farther into BGP theory
let’s get a configuration started. You’ll use the router bgp command to configure a router as a BGP speaker. Right after that
the neighbor command will be used to identify this BGP speaker’s potential neighbors. (The terms "peer" and "neighbor" are interchangeable in BGP
but it's the neighbor statement that is used to statically define neighbors. BGP is not capable of discovering neighbors dynamically.)

R1(config-router)#neighbor 172.12.123.3 remote-as 200

While almost all of the neighbor options are just that -- optional -- you do have to specify the BGP AS of the remote router. BGP has no mechanism to dynamically discover neighbors. Remember
BGP speakers do not have to be in the same AS to become peers. To verify that the remote BGP speaker has become a peer
run show ip bgp neighbor.


R1#show ip bgp neighbor

BGP neighbor is 172.12.123.3
remote AS 200
external link

BGP version 4
remote router ID 0.0.0.0

BGP state = Active

Last read 00:01:39
hold time is 180
keepalive interval is 60 seconds

Received 0 messages
0
notifications
0
in queue

Sent 0 messages
0
notifications
0
in queue

Route refresh request: received 0
sent 0

Default minimum time between advertisement runs is 30 seconds

The output here can be a little misleading the first time you read it. The first highlighted line shows 172.12.123.3 is a BGP neighbor
is located in AS 200
and is an external link
indicating that the neighbor is in another AS entirely. The second highlighted line shows the BGP state as Active. This sounds great
but it actually means that a BGP peer connection does not yet exist with the prospective neighbor.

So even though the show ip bgp neighbor output indicated that this is an Active neighbor relationship
that’s not as good as it sounds. Of course
the reason the peer relationship hasn’t been established is that we haven’t configured R3 yet!


R3(config)#router bgp 200
R3(config-router)#neighbor 172.12.123.1 remote-as 100

Verify the peer establishment with show ip bgp neighbor:

R3#show ip bgp neighbor

BGP neighbor is 172.12.123.1
remote AS 100
external link

BGP version 4
remote router ID 172.12.123.1

BGP state = Established
up for 00:01:18

Last read 00:00:17
hold time is 180
keepalive interval is 60 seconds

Local host: 172.12.123.3
Local port: 179 (BGP uses TCP Port 179)

Foreign host: 172.12.123.1
Foreign port: 11007
The peer relationship between R1 and R3 has been established.

Now that you know how the neighbor relationship itself is built
you need to start learning the many options of the neighbor command. You’ll have to master these to become a CCNP and CCIE!

Passing the BSCI exam and earning your CCNP is all about knowing the details
and when it comes to EIGRP SIA routes
there are plenty of details to know. A quick check in a search engine for "troubleshoot SIA" will bring up quite a few matches. Troubleshooting SIA routes is very challengin in that there's no one reason they occur.

View the EIGRP topology table with the show ip eigrp topology command
and you'll see a code next to every successor and feasible successor. A popular misconception is that we want these routes to have an "A" next to them - so they're active. That's what we want
right? Active routes sound good
right?

Well
they sound good
but they're not. If a route shows as Active in the EIGRP topology table
that means that DUAL is currently calculating that route
and it's currently unusable. When a route is Passive ("P)
that means it's not being recalculated and it's a usable route.

Generally
a route shown as Active is going to be there for a very short period of time by the time you repeat the command
hopefully that Active route has gone Passive. Sometimes that doesn't happen
though
and the route becomes SIA - Stuck In Active.

A route becomes SIA when a query goes unanswered for so long that the neighbor relationship is reset. From experience
I can tell you that troubleshooting SIA routes is more of an art form than a science
but there are four main reasons a route becomes SIA:

The link is unidirectional
so the query can't possibly be answered.

The queried router's resources are unavailable
generally due to high CPU utilization.

The queried router's memory is corrupt or otherwise unable to allow the router to answer the query.

The link between the two routers is of low quality
allowing just enough packets through to keep the neighbor relationship intact
but not good enough to allow the replies through.

To sum it up
routes generally become SIA when a neighbor either doesn't answer a query
or either the query or reply took a wrong turn somewhere. I told you it wasn't the easiest thing to troubleshoot!

When you're working on your BCMSN exam on your way to CCNP certification
you'll read at length about how Cisco routers and multilayer switches can work to provide router redundancy - but there's another helpful service
Server Load Balancing
that does the same for servers. While HSRP
VRRP
and CLBP all represent multiple physical routers to hosts as a single virtual router
SLB represents multiple physical servers to hosts as a single virtual server.

In the following example
three physical servers have been placed into the SRB group ServFarm. They're represented to the hosts as the virtual server 210.1.1.14.

The hosts will seek to communicate with the server at 210.1.1.14
not knowing that they're actually communicating with the routers in ServFarm. This allows quick cutover if one of the physical servers goes down
and also serves to hide the actual IP addresses of the servers in ServFarm.

The basic operations of SLB involves creating the server farm
followed by creating the virtual server. We'll first add 210.1.1.11 to the server farm:

MLS(config)# ip slb serverfarm ServFarm

MLS(config-slb-sfarm)# real 210.1.1.11

MLS(config-slb-real)# inservice

The first command creates the server farm
with the real command specifying the IP address of the real server. The inservice command is required by SLB to consider the server as ready to handle the server farm's workload. The real and inservice commands should be repeated for each server in the server farm.

To create the virtual server:

MLS(config)# ip slb vserver VIRTUAL_SERVER

MLS(config-slb-vserver)# serverfarm ServFarm

MLS(config-slb-vserver)# virtual 210.1.1.14

MLS(config-slb-vserver)# inservice

From the top down
the vserver was named VIRTUAL_SERVER
which represents the server farm ServFarm. The virtual server is assigned the IP address 210.1.1.14
and connections are allowed once the inservice command is applied.

You may also want to control which of your network hosts can connect to the virtual server. If hosts or subnets are named with the client command
those will be the only clients that can connect to the virtual server. Note that this command uses wildcard masks. The following configuration would allow only the hosts on the subnet 210.1.1.0 /24 to connect to the virtual server.

MLS(config-slb-vserver)# client 210.1.1.0 0.0.0.255

SLB is the server end's answer to HSRP
VRRP
and GLBP - but you still need to know it to become a CCNP! Knowing redundancy strategies and protocols is vital in today's networks
so make sure you're comfortable with SLB before taking on the exam.

To pass the CCNP exams
you’ve got to master Quality of Service
and the first step in doing so is knowing the differences between the different QoS types.

Now this being Cisco
we can't just have one kind of QoS! We've got best-effort delivery
Integrated Services
and Differentiated Services. Let's take a quick look at all three.

Best-effort is just what it sounds like - routers and switches making their "best effort" to deliver data. This is considered QoS
but it's kind of a "default QoS". Best effort is strictly "first in
first out" (FIFO).

An entire path from Point A to Point B will be defined in advance when Integrated Services are in effect. Integrated Services is much like the High-Occupancy Vehicle lanes found in many larger cities. If your car has three or more people in it
you're considered a "priority vehicle" and you can drive in a special lane with much less congestion than regular lanes. Integrated Services will create this lane in advance for "priority traffic"
and when that traffic comes along
the path already exists. Integrated Services uses the Resource Reservation Protocol (RSVP) to create these paths. RSVP guarantees a quality rate of service
since this "priority path" is created in advance.

Integrated Services is defined in RFC 1613. Use your favorite search engine to locate a copy online and read more about this topic. It's a good idea to get into the habit of reading RFCs!

Of course
if you've got a lot of different dedicated paths being created that may or not be used very often
that's a lot of wasted bandwidth. That leads us to the third QoS model
the Differentiated Services model. Generally referred to as DiffServ
there are no advance path reservations and there's no RSVP. The QoS policies are written on the routers and switches
and they take action dynamically as needed. Since each router and switch can have a different QoS policy
DiffServ takes effect on a per-hop basis rather than the per-flow basis of Integrated Services. A packet can be considered "high priority" by one router and "normal priority" by the next.

Believe me
this is just the beginning when it comes to Quality of Service. It's a huge topic on your exams and in the real world's production networks
and as with all other Cisco topics
just master the fundamentals and build from there - and you're on your way to CCNP exam success!

To earn your CCNP certification and pass the BCMSN exam
you've got to know what HSRP does and the many configurable options. While the operation of HSRP is quite simple (and covered in a previous tutorial)
you also need to know how HSRP arrives at the MAC address for the virtual router - as well as how to configure a new MAC for this virtual router. This puts us in the unusual position of creating a physical address for a router that doesn't exist!

The output of show standby for a two-router HSRP configuration is shown below.

R2#show standby

Ethernet0 - Group 5

Local state is Standby
priority 100

Hellotime 3 sec
holdtime 10 sec

Next hello sent in 0.776

Virtual IP address is 172.12.23.10 configured

Active router is 172.12.23.3
priority 100 expires in 9.568

Standby router is local

1 state changes
last state change 00:00:22

R3#show standby

Ethernet0 - Group 5

Local state is Active
priority 100

Hellotime 3 sec
holdtime 10 sec

Next hello sent in 2.592

Virtual IP address is 172.12.23.10 configured

Active router is local

Standby router is 172.12.23.2 expires in 8.020

Virtual mac address is 0000.0c07.ac05

2 state changes
last state change 00:02:08

R3 is in Active state
while R2 is in Standby. The hosts are using the 172.12.123.10 address as their gateway
but R3 is actually handling the workload. R2 will take over if R3 becomes unavailable.

An IP address was assigned to the virtual router during the HSRP configuration process
but not a MAC address. However
there is a MAC address under the show standby output on R3
the active router. How did the HSRP process arrive at a MAC of 00-00-0c-07-ac-05?

Well
most of the work is already done before the configuration is even begun. The MAC address 00-00-0c-07-ac-xx is reserved for HSRP
and xx is the group number in hexadecimal. That's a good skill to have for the exam
so make sure you're comfortable with hex conversions. The group number is 5
which is expressed as 05 with a two-bit hex character. If the group number had been 17
we'd see 11 at the end of the MAC address - one unit of 16
one unit of 1.

The output of the show standby command also tells us that the HSRP speakers are sending Hellos every 3 seconds
with a 10-second holdtime. These values can be changed with the standby command
but HSRP speakers in the same group should have the same timers. You can even tie down the hello time to the millisecond
but it's doubtful you'll ever need to do that.

R3(config-if)#standby 5 timers ?

<1-254> Hello interval in seconds

msec Specify hello interval in milliseconds

R3(config-if)#standby 5 timers 4 ?

<5-255> Hold time in seconds

R3(config-if)#standby 5 timers 4 12

Another important HSRP skill is knowing how to change the Active router assignment. I'll show you how to do that
and how to configure HSRP interface tracking
in the next part of my CCNP / BCMSN exam tutorial!

Defined in RFC 2281
HSRP is a Cisco-proprietary protocol in which routers are put into an HSRP router group. Along with dynamic routing protocols and STP
HSRP is considered a high-availability network service
since all three have an almost immediate cutover to a secondary path when the primary path is unavailable.

One of the routers will be selected as the primary ("Active"
in HSRP terminology)
and that primary will handle the routing while the other routers are in standby
ready to handle the load if the primary router becomes unavailable. In this fashion
HSRP ensures a high network uptime
since it routes IP traffic without relying on a single router.

The hosts using HSRP as a gateway don't know the actual IP or MAC addresses of the routers in the group. They're communicating with a pseudorouter
a "virtual router" created by the HSRP configuration. This virtual router will have a virtual MAC and IP adddress as well.

The standby routers aren't just going to be sitting there
though! By configuring multiple HSRP groups on a single interface
HSRP load balancing can be achieved.

Before we get to the more advanced HSRP configuration
we better get a basic one started! We'll be using a two-router topology here
and keep in mind that one or both of these routers could be multilayer switches as well. For ease of reading
I'm going to refer to them only as routers.

R2 and R3 will both be configured to be in standby group 5. The virtual router will have an IP address of 172.12.23.10 /24. All hosts in VLAN 100 should use this address as their default gateway.

R2(config)#interface ethernet0

R2(config-if)#standby 5 ip 172.12.23.10

R3(config)#interface ethernet0

R3(config-if)#standby 5 ip 172.12.23.10

The show command for HSRP is show standby
and it's the first command you should run while configuring and troubleshooting HSRP. Let's run it on both routers and compare results.

R2#show standby

Ethernet0 - Group 5

Local state is Standby
priority 100

Hellotime 3 sec
holdtime 10 sec

Next hello sent in 0.776

Virtual IP address is 172.12.23.10 configured

Active router is 172.12.23.3
priority 100 expires in 9.568

Standby router is local

1 state changes
last state change 00:00:22

R3#show standby

Ethernet0 - Group 5

Local state is Active
priority 100

Hellotime 3 sec
holdtime 10 sec

Next hello sent in 2.592

Virtual IP address is 172.12.23.10 configured

Active router is local

Standby router is 172.12.23.2 expires in 8.020

Virtual mac address is 0000.0c07.ac05

2 state changes
last state change 00:02:08

We can see that R3 has been selected as the Active router ("local state is Active")
the virtual router's IP is 172.12.23.10
and R2 is the standby router.

There are some HSRP values that you'll need to change from time to time. What if we want R2 to be the Active router instead? Can we change the MAC address of the virtual router? I'll answer those questions in the next part of this HSRP tutorial!