They link state request requesting fool elysée information from the neighboring Rodda the neighboring
Radi will send what's called a link State Update which is a packet that contains links state advertisements.
And as mentioned is typically sent in response to link state request.
This contains detailed information about the link state database rather than just an overview of it
which was contained in the database description links that acknowledgements acknowledge or confirm receipt
of the link state update message.
Now an autonomous system is a grouping of rodders under communist Ministry of domain.
So let's assume that the rod is contained within the loop portion of running OSPF within a single autonomous
system.
They may be connecting to other routers under another administer of domain or another company's control
that is running rUK for example OSPF is an IGP on T-Ray gateway protocol.
In other words it's used within an autonomous system.
So within your organization you may have multiple routers running OSPF within the same antonymous system.
For scalability OSPF networks are broken up into areas.
Now there's debate about this but Cisco would recommend never more than 50 routers with a single OSPF
area.
In your studies in the future you may come across different figures but that's a good rule of thumb
to use OSPF uses her Rockhill model in that you always have OSPF areas zero when you have more than
one area.
It is possible to run OSPF in a another area.
Let's say Area 1 but that's only true if you have a single area.
If you've got multiple areas you have to have Area zero which is known as the backbone area.
All traffic from one area to area one to another area let's say Area T will traverse the backbone.
So what you do is you break up your network into multiple areas following the physical topology with
a view to optimize summarization and reduce routing table updates and link state advertisements.
Certain types of LSA can be contained within an area so the flooding of elysées throughout the network
is stopped by breaking up the network into multiple areas routers that border the backbone area and
another area unknown area of border routers for AVR.
The three routers highlighted here are ABRSM because they have one interface in area zero and another
interface in another area.
One of the advantages of AB RS is that they allow for a summarization of routes.
If Area 1 contains Rutz 10 1 1 0 up to 10 1 100 0 and an area t.
We have networks 10 to 1 0 up to 10 to 100 Ceara and Area 3 10 3 1 0 up to 10 3 100 0.
Those routes can be summarized on AB rs.
You could say these 100 Rutz will be summarized as a single wrocht on this AVR says Lesch 60 Maust is
used to summarize these 100 drafts.
The same could be done here 10 to 007 16 is a summary of these ruts and last 10 3 0 0 is that 16 is
a summary of these rocks.
This doesn't require careful planning and good IP design.
Misrata is known as an autonomous system border Rodda for SDR.
It borders two autonomous systems.
In this case we've got rep on the left hand side and OSPF on the right hand side.
Even if all of these routers including the router where within your organization this router would still
be known as an ISP or because it's connecting one routing process up to another writing process.
In this case OSPF So from an OSPF point of view this is an autonomous system for the router.
The six routers all have interfaces within area zero and therefore are known as backbone routers.
When traffic is sent from one area to another area it has to traverse the backbone to reach the destination.
So these three Raptor's in the backbone are used to allow the traffic to flow from area one to area
to OSPF once again requires a good design with all areas connecting to the backbone area as traffic
flows from one area to another area through the backbone area.
These highlighted routers are known as internal routers.
They are internal to they specific areas.
OSPF routers use Halo's to form neighbor relationships or adjacencies the hello protocol once again
establishes and maintains neighbor relationships by ensuring bi directional.
In other words two way communication between neighbors.
Bi directional communication occurs when a router recognizes itself listed in the packet received from
a neighbor or S. using multicast address 2 2 4 0 0 5 and contain the following information.
Whenever relationships to be formed it's important to remember that certain parameters have to match
on both routers.
Now the first field contained in a hollow is the router ID a router ID identifies the specific router
and is used in various scenarios in OSPF computing the election of a designated router or backup designated
Rodda a router ID is chosen per router based on the highest IP address of any configuring to face when
OSPF is enabled on the router or on the highest loopback interface active on the router.
When OSPF is enabled or it can be manually specified using the Rodda ID command.
So to demonstrate that you have Harada Rotto one show at the interface brief will show me the relevant
interfaces in Misrata.
What I'm going to do is I'm going to shut down all the interfaces and show you that OSPF is not able
to select a router ID if the interfaces all shut down.
So show IP interface brief again shows me that all of my interfaces are masterly shut non-global config
mode popping the command Rodda this case OSPF and a Proteus ID will allow me to enable OSPF on this
router.
The process ID allows for the differentiation of multiple OSPF instances running on the same router
that can become important in multi protocol labels switching environments or imperialis environments.
For this cause you'll only run a single OSPF process on a router but note multiple processes can be
enabled on erotic.
Now notice what the Rhodes's know Rodda ID OSPF process one fail to allocate a unique Urara ID and therefore
cannot start topping the come on do show IP protocol shows that the routing protocol in use is OSPF
one but the Rodda ID is 0 0 0 0 OSPF is not running directly on this route it show IP interface brief
lets enable this interface interface 00.
No shut.
So what L.D. is all remove Is.
And then I'll re-enable OSPF
notice there's no complaint to show IP protocols shows me that the Rodda ID is 10 1 1 1 to show ID to
face brief shows me that this IP address has become the Rodda ID.
The reason why it is the Rodda ID is chosen based on the highest IP address of any active interface.
When the writing process is enabled safe enabled for instance these two interfaces
as follows.
And then top the Kim on do show the interface brief.
You'll see that these interfaces the fast Ethan interface and the two serial interfaces all up up do
show Ickey protocols still shows that the Rodda ID is 10 1 1 1 just change the encapsulation back to
its default.
So I still see and the interfaces come up again.
But what I'd like to see is that the Rodda Id still remains as 10 1 1 1 and I could do that command
again to show IP protocols.
Notice the Rodda IDs 10 1 1 1 I can do this come on clear IP OSPF process to clear the OSPF process.
Let's see if that makes any difference.
So show IP protocol and as you can see the Rodda I.D. remains the same.
But if I remove OSPF and then re-enabled OSPF
noticed the Rodda idea has changed to 10 1 5 1.
So what the Rodda has done is it looked for the highest IP address on any active interface.
When OSPF was enabled this time when OSPF was enabled 10 1 5 1 was the highest IP address on any active
physical interface.
So it was chosen as the Rodda ID.
Now what happens if we enable the loopback.
You'll notice the loopback has the lowest IP address.
One is far lower than 10 so no shut that you show IP protocol.
You can see there ATA IDs stole 10 1 5 1 0 good again wrong ideas still 10 1 5 1.
But if I remove OSPF and then re-enable it
noticed serrata ID is now quadruple one.
So the rule again OSPF route ID is chosen based on the highest IP address of any physical interface
that is active.
When the OSPF process is enabled.
But if there is a loopback that is active the loopback overrides the physical interfaces and the loopback
is used as the Rodda ID loop BAC's have the advantage that they never go down a list manually shut down.
This has multiple advantages including stability.
Mahratta ID was originally 10 1 1 1 and the router reloaded assuming that there were no loop checks
enabled the Rodda ID would have changed to 10 1 5 1.
So the Rodda ID number could have changed back the loopback ID would remain as quadruple one as long
as there were no other loop BACS configured on this router.
So it doesnt matter what the physical interfaces are set to.
Its recommended to set the Rodda ID manually using this command and set it to a relevant loopback.
In this case I'm just going to set it to some arbitrary value to show you that you can set it to 1 2
1 6 8 1 and 1 which is not an IP address from a local wrote it to show IP protocol allows me to see
that the to ID is 1 2 1 6 8 1 to 1.
Now it's recommended practice to set the Rodda I.D. to one of the loot banks on your Rodda.
So I'm going to set the Rodda I.D. to quadruple one
as you can see yeah the Rodda IDs changed to quick ripple one the hello packet then contains the hello
and did intervals which must be the same on both routers.
Otherwise an adjacency or neighbor relationship will not be form.
It then contains the list of neighbors that the router knows about.
That's our data knows if there is two way communication because it recognizes itself in the list of
neighbors that it receives in the hollow packet it then contains the area ID which must also match on
both routers.
It then contains a router property which can be used in designate a rotten backup designated Rodda elections.
It then contains the designate Harada or D or IP address backup designate Harada or DDR IP address.
We're going to talk more about designator rodders and backup designated routers in a moment.
It then contains the indication password.
Now there are various ways to set up a syndication including clear text and in the five Hession.
We'll talk more about those later.
The indication password needs to be the same otherwise the relationship will not be formed.
And then Lawsie the stub area flag needs to be the same the step area flag denotes whether this is a
stub area or a normal area.
We'll talk more about stub areas once again in later slides.