A link state request requesting full LSA information from the neighboring Rada the neighboring Rada
will send what's called a linked state update which is a packet that contains links that advertisements
and as mentioned is typically sent in response to a linked 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 state acknowledgements acknowledge or confirm
receipt of the link state update.
Message an autonomous system is a grouping of rorters under common administrative domain.
So let's assume that the rot is contained within the blue portion or running of SPF within a single
autonomous system.
They may be connecting to other orders under another administer of domain or another company's control
that is running up for example o SPF is an IGP Ontario Gateway Protocol.
In other words it's used within an autonomous system so within your organization you may have multiple
routers running SDF within the same autonomous system for scalability OSP if networks are broken up
into areas.
Now there's debate about this but Cisco would recommend never more than 50 routers within a single SDF
area.
In your studies in the future you may come across different figures but that's a good rule of thumb
to use 0 SPF uses a hierarchical model in that you always have a SPF area 0 when you have more than
one area.
It is possible to run a SPF in 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 2 will traverse the backbone so what you do is you break up your network into multiple
areas following the physical topology with the view to optimize summarization and reduce routine table
updates and links state advertisements.
Certain types of LSA can be contained within an area so the flooding of LSA is throughout the network
is stopped by breaking up the network into multiple areas routers that border the backbone area and
another area are known as Area border routers or a B Rs the 3 rod is highlighted here or a bypass because
they have one interface in area zero and another interface in another area.
One of the advantages of AP RS is that they allow for summarization of routes if aerial 1 contains ruts
10 1 1 0 up to 10 1 100 0 and an area 2.
We have need to extend to 1 0 up to 10 to 100 0.
An area 3 10 3 1 0 up to 10 3 100 0.
Those routes can be summarized on a Rs so you could say these 100 rods will be summarized as a single
rod on this ADR so slash 60 lost is used.
To summarize these hundred drops the same could be done yeah.
10 to 00 such 16 is a summary of these ruts.
And lastly 10 3 0 0.
That 16 is a summary of these rocks.
This does require careful planning and good IP design.
This Rada is known as an autonomous system Bodo Rada or ACR.
It borders two autonomous systems.
In this case we've got rip on the left hand side and 0 SDF on the right hand side.
Even if all of these rowdies including the rip Rada were within your organization this Rada would still
be known as an ISP or because its connecting one routing process up to another writing process.
In this case of SPF.
So from an O SPF point of view this is an autonomous system.
Order Roorda these six riders all have interfaces within area zero and therefore 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 rafters in the backbone are used to allow the traffic to flow from area one to Area 2
0 SPF 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 roads are known as internal
routers they are internal to their specific areas ISP for orders use hellos 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 rider
recognizes itself listed in the hello packet received from a neighbor.
Others are sent using multicast address 2 2 4 0 0 5 and contain the following information for neighbor
relationships to be formed.
It's important to remember that certain parameters have to match on both riders.
Now the first field containing a hello is the router I.D. a router I.D. identifies the specific router
and is used in various scenarios in SPF including the election of a designated Raptor or backup designated
Rata a router I.D. is chosen per router based on the highest IP address of any configured interface.
When SPF is enabled on the router or on the highest loop back interface active on the router when 0
SPF is enabled or it can be manually specified using the Rada I.D. command so to demonstrate that you
have a rod Rado 1 show off the interface brief will show me the relevant interfaces on the strata and
what I'm going to do is I'm going to shut down all the interfaces and show you that OSP is not able
to select a router I.D. If the interfaces are all shut down
so show IP interface brief again shows me that all of my interfaces are administratively shut down global
config mode topping the command Rada in this case 0 SPF and a protest I.D. will allow me to enable a
if on this router the process I.D. allows for the differentiation of multiple OSP if instances running
on the same Rata that can become important in multiple protocol label switching environments or NPL
place environments for this course you'll only run a single Oh SPF process on a router but note multiple
processes can be enabled on our audit now notice what the road is says no Ruda I.D..
Oh SPF process one failed to allocate a unique Rada I.D. and therefore cannot start topping.
Come on do show IP protocol shows that the routing protocol in use is 0 SPF 1 but the Rada I.D. is 0
0 0 0.
0 SPF is not running correctly on this route to show IP interface brief lets enable this interface so
interface is 0 0.
No shut.
So what I'll do is I'll remove SPF and then I'll rename below SPF
notice there's no complaint to show IP protocols shows me that the Rada I.D. is 10 1 1 1 to show of
the interface brief shows me that this IP address has become the Rada I.D..
The reason why is the Rada I.D. is chosen based on the highest IP address of any active interface.
When their writing process is enabled.
So if I enabled for instance these two interfaces
as follows and then top to command do show IP interface brief
you'll see that these interfaces the first Ethan interface and the two serial interfaces are up up do
show IP protocols schools shows that the Rada I.D. is 10 1 1 1 I've just changed the encapsulation back
to its default so I still see and the interfaces come up again.
But what I'd like you to see is that the Rada I.D. still remains as 10 1 1 1 and I can do that command
again to show IP protocols notice the Rada I.D. 10 1 1 1 I can do this Come on clear IP 0 SPF process
to clear the 0 SPF process and let's see if that makes any difference.
So show IP protocol and as you can see the Rada I.D. remains the same but if I removed I was P.F. and
then rename old or SPF
noticed the Rada ideas changed to 10 1 5 1 So what the Rada has done is it looked for the highest IP
address on any active interface.
When 0 SPF was enabled this time when 0 SPF was enabled 10 1 5 1 was the highest IP address on any active
physical interface so it was chosen as the Rada I.D..
Now what happens if we enable the loop back you'll notice the loop back has the lowest IP address one
is far lower than 10 so no shot that you show IP protocol you can see the Rada I.D. stole 10 1 5 1 0
do it again.
Right I.D. is still 10 1 5 1 but if I remove 0 SPF and then re enable it
notice the Rada ideas now quadruple 1
so the rule again 0 SPF Rada I.D. is chosen based on the highest IP address of any physical interface
that is active when the SPF process is enabled.
But if there is a loop back that is active the loop back overrides the physical interfaces and the loop
back is used as the Rada I.D. loop ex have the advantage that they never go down unless manually shut
down.
This has multiple advantages including stability.
If my Rada I.D. was originally 10 1 1 1 and the right to reloaded assuming that there were no loop backs
enabled the Rada idea would have changed to 10 1 5 1.
So the Rada I.D. number could have changed but with the loop back the Rada I.D. would remain as quadruple
1.
As long as there were no other loop ex configured on the strata so it doesn't matter what the physical
interfaces or safety it recommended to set the Rada I.D. manually using this command and set it to a
relevant loop back.
In this case I'm just going to set it to some arbitrary value to show you that you can set it to 1 9
2 1 6 8 1 not 1 which is not an IP address on my local rata to show IP protocol allows me to see that
the Rada I.D. is 1 9 2 1 6 8 1 1.
Now it's recommended practice to set the Rada I.D. to one of the loot banks on your Rada.
So I'm going to set the Rada I.D. to quadruple 1
as you can see yeah.
The Rada ideas changed to quadruple 1 the hello packet then contains the hello and did intervals which
must be the same on both rowdies is otherwise an adjacency or neighbour relationship will not be formed.
It then contains the list of neighbours that the rotten knows about.
That's our rotten nose.
If there's two way communication because it recognises itself in the list of neighbours that it receives
in the hello packet it then contains the area I.D. which must also match on both fraud as it then contains
a rod of property which can be used in designated route and backup designated Rada elections.
It then contains the designated Rada or D or IP address backup designate Rada or DDR IP address.
We're going to talk more about designated routers and backup designated routers in a moment.
It then contains the authentication password.
Now there are various ways to set up authentication including clear text and Indy five hashing.
We'll talk more about those later.
The authentication password needs to be the same.
Otherwise the relationship will not be formed.
And then lastly 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.