Open shortest path first or SPF 0 SPF is an industry standard powerful routing protocol used in many
networking environments in the world today.
The word open means that it's an open standard.
This is a great advantage to using 0 SPF because of vendor interoperability.
You can make Cisco routers with Nortel routers HP routers and others and be assured their rights will
be exchanged between the different vendors shortest path first or SPF also known as the Dykstra algorithm
named after the developer who published the algorithm in 1959 is used by SPF to determine the shortest
path or best route to a destination.
So what we're going to cover is firstly an overview of SPF and we look at the features of OSP.
I'd like to show you how to set up a network using a single O SPF area.
I going to show the importance of loop backs and how they determine the Rada I.D. We'll look at quite
a few configurations and setups and oh SPF including multiple area of SPF and authentication 0 SPF once
again is a link state routing protocol and will flood links that advertisements or else essays throughout
the network or area describing firstly the links attached to Arata.
In other words the writing interfaces and the state of those links the state meaning a description of
an interface and its relationship to neighboring routers is the interface up or is the interface down
that description would include for example the IP address of the interface the subnet mask the type
of network to which it is connected and the rudders that are connected to that network and so forth
the collection of all of these linked states forms the top a logical database or linked state database
routers form neighbor relationships by sending out hello messages using either multicast address 2 2
4 0 0 5 or unique costs.
LSA is once again a flooded throughout the network or area and the links state database is created from
these links that advertisements or LSD OSB if once again uses the shortest path first algorithm or Dykstra
is algorithm to determine the best path to each destination.
Now there's a bit of debate about this.
Engineers will often discuss where in the OS and model various protocols reside.
SPF resides directly on top of IP or SPF does not use or UDP for transporting of updates and information
it resides directly on top of IP OSB if is referenced in the IP header with protocol I.D. 89 DCP reference
with protocol 86 and UDP protocol I.D. 17 and thus some would debate that ISP if resides at Layer 4
for this course however we are going to say that OSP resides at Layer 3 directly on top of IP.
Also at Layer 3 for a lot of us in the real world this isn't a major concern but maybe from a theoretical
point of view.
He has a wide shot capture showing various SPF packets so as an example this first one is from Iran
too with an IP address of 10 1 1 1 Going to the well-known multicast address for 0 SPF 2 2 4 0 0 5 so
that's the address used by ISP for hellos on for instance and Ethan its segment and you can see in the
output here at Layer 2 We've got the source MAC address of the router sending information to an IP version
for multicast address.
In this case the well-known multicast address for a wispy if Adelaide to the ether type is 0 800 in
hexadecimal.
In other words referencing IP
at layer three.
We've got the source IP address once again of 10 1 1 1 and destination of 2 2 4 0 0 5.
You can see this is an IP version of full packet and you can see here.
The protocol I.D. is 0 SPF in hexadecimal referenced as 0 x 5 9 using a Windows calculator.
We consider to use hexadecimal set the value of fifty nine and then change it to decimal and you can
see the protocol I.D. is eighty nine.
So at least three hours P.F. is referenced with protocol I.D. 89.
The source once again is 10 1 1 1 destination is the multicast address 4 0 SPF residing directly on
top of IP is 0 SPF so notice we have Ethernet IP 0 SPF 0 SPF does not use TTP or UDP as a transport
it uses IP you can see the 0 SPF header version two of our SPF you can see that this is a hello packet.
In other words Type 1 you can see it's for area 0 0 SPF areas can be referenced either as single decimal
numbers like 0 or in dotted IP decimal notation as in 0 0 0 0.
It's like saying tomorrow or tomorrow it's the same thing you can see the sources 10 1 1 1 you can see
it's a hello packet is information like the network mosque the hello interval the a priority the route
a date interval to the designated road is to the back of designate a road is who the active neighbour
is and so forth.
We're going to cover a lot of this information in the upcoming slides the important thing to note is
once again is that oh SPF resides directly on top of IP.
If we look at the next message we're out at 10 1 1 2 is sending a database description to rout at 10
1 1 1.
You'll see once again that there is no TCO or UDP or SPF is reference with protocol i.e. eighty nine
in an IP vision for header always before this course resides at layer 3.
But as mentioned is a bit of debate about exactly where it resides Arata sends links that advertisements
to advertise the state of the link immediately when the state changes or periodically by default.
Every 30 minutes the databases will be synchronized with the State of the links ISP of routers from
neighbor relationships and the list of neighbors is stored in the adjacency table or SPF neighbor table
so topping the command show IPO SPF neighbors will show you adjacent neighbors or SPF uses multicast
addresses 2 2 4 0 0 5 and 2 2 4 0 0 6 which are linked local multicast.
In other words those multicast cannot hop across the road.
The writers have to be directly connected always fearful store all routes learned in the OSP of topology
database or link state database link state database contains all routers and attached links in the area
or network all OSB of routers in the same area share the same database.
Best Routes are then put into the writing table also known as the forwarding table.
There are various packet types used in ours.
The first type is A Hello packet which is used firstly to dynamically discover neighbours and secondly
to form neighbor relationships and maintain those neighbor relationships.
The awesome default intervals for hellos on broadcast multimedia segments such as Ethernet the interval
is 10 seconds.
The second default interval is 30 seconds which is used on non broadcast segments such as serial links.
An MBA may non broadcast multi axis environments such as frame relay 0 SPF has what's called a dead
interval or dead timer which is four times the hello interval by default.
If you change the hello interval 0 is fearful automatically change the date interval to value 4 times
the hello interval on a specific interface.
So how close are used to discover neighbours.
And if a hello is not received within the date interval the neighbour relationship is torn down because
it's deemed that the neighbour is no longer available.
The second type of packet is what's called a database description written as DDR or DVD which is used
to exchange brief versions of each link state advertisement SPF is a linked state writing protocol riders
exchange information about the state of links through link state advertisements.
When an initial relationship is formed between two two SPF routers they will exchange database descriptions
giving each other an overview of what the database contains.
If parts of the database are missing on one router it will send a link state request requesting full
LSA information from the neighboring router 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 links state database rather than just an overview of it
which was contained in the database description link state acknowledgements acknowledge or confirm receipt
of the link state update.
Message.