This is one of multiple videos discussing a multi area of SPF.
This is both a troubleshooting as well as an explanation of video.
We've been told in this topology that brought of one on the left is not able to ping Rada six on the
right rather one is running G.I. joe p So the command show IP protocols shows us that the only writing
protocol enabled on this Rada is EAI GOP on brought a 6 show IP protocols shows us that 0 SPF is enabled
on rota 6.
We can also see that the router has a loop back address of 6 6 6 6 so quadruple 6 can write a 1 ping
that address and the answer is no pings or failing
all disable IP domain lock up to speed things up and let us to trace to that loop back after the moment
to the trace is going nowhere.
I'll do a debug IP package to see what happens and I'll ping with only one paying to that address so
ping six dot six 266.
Repeat.
1 and let's do that again.
And I'll turn off debugging notice here.
Source one wondered wondered one pinging 66 at 66.
We're told that it's unreadable these other messages or even GOP messages.
The ping is unsuccessful to show IP round shows us that the vector network doesn't exist in the routing
table.
If we try and ping tendered one to five but one that also fails and sodas tendered one that five to
two.
So we can't paying this network all the loop back of wrought a six.
What about the loop back of wrought a five.
So we able to ping the loop back around a five but not the loop back about a six.
And if we trace to tendered wondered five that one the trace fails immediately because the right doesn't
exist in the routing table tendered one dot 4.0 does exist in the routing table so we can paying tendered
wondered for that one as well as tendered wondered forward to.
In other words we can get to this network.
Now again we are running EAI GOP on this router so these rorts have been redistributed from USPS into
EAI GOP let's look at right it too and see if wrote too can ping the loop back of Roorda 6.
It's not able to do that.
So show IP ranch.
We are not seeing that looped back in the routing table so let's have a look at what 5 Ken wrote a 5
paying the loop back of road 6.
The answer is it can.
So show IP wrote it's able to ping the loop back around a 6 the loop back exists as an OSP front in
the writing table of route of 5.
What about brought a 4
paying loop back of wrote a 6 that ping fails.
Show IP round back to loop packet doesn't exist in the writing table.
So let's have a look at route of 5 by using the command show IP protocols and tell me if you can see
the problem by looking at this output.
What do you think is the problem when you look at the sound.
Put and to give you a hint.
I'll do the same command on en route for show IP protocols en route a full there's the output for a
for yes the output for road of 5.
What's the problem with this configuration okay.
So notice the following its routing for areas of 1 and 2 the strata has interfaces in multiple areas
but doesn't have area 0 configured so show run Section 0 SPF shows us that the router is configured
for area 1 and area 2 but is not configured for area 0.
Router 4 is configured for Area 1 it's a requirement in 0 SPF that area 0 be connected to other areas.
In other words this is configured as Area 1 This is configured as Area 2 but Area 2 is not adjacent
or bordering area 0.
That's a problem if we look at router 3 over here.
Show IP protocols we can see that this Rada is configured as an area border router it has interfaces
an area 0 and interfaces in Area 1 to show IP SPF interface brief shows us that gigabit 00 is configured
in area 0 gigabit 0 1 is configured in Area 1 so that looks good but rather 5 isn't configured in that
way.
So show IP SPF interface brief.
Notice it has interfaces in Area 1 and Area 2 but not in area 0.
That's why write a 1 campaign the loop back of route of 4 and the loop back of route of 5 but not the
loop back of road a 6 because
SPF is correctly configured with area 0 and Area 1 Over here.
It works but here we have a problem.
We need to create what's called a virtual link between Rider 3 and route of 5.
So we have to essentially pull or extend area 0 from Rider 3 to write a 5 to make road a 5 an area of
border rider so we will be essentially creating a tunnel where area 0 traverses a cross Area 1 2 write
a 5 area zero is going to be tunneled across Area 1 so that route of 5 becomes an area border rider
which means that area 2 is adjacent to area 0 that is required in 0 SPF.
All areas have to be adjacent to area 0 when you have multiple SPF areas so show run section of SPF.
We can see the configuration of Road 3.
Now when you create your virtual links you have to configure the other side using the Rada I.D. not
the IP address of the rota but the Rada I.D. So the command show IP SPF interface will show us the local
routers Rada I.D. So the right I.D. is 3D or tree to tree to tree.
You can also use the command show IPO SPF and we'll be able to see that draw to I.D. So notice Rada
I.D. 3.0 3 2 3 2 3 on route 5 show IP 0 SPF.
The right idea is 5.5.
At 5.5 so background brought a 3 show run Section 0 SPF
that's the configuration of SPF on Route 3 and that's the configuration of wrought a five some road
a three Roorda or SPF.
One area one.
This is the area that we are traversing the virtual link and the neighbors Roorda I.D. is 5 to 5 at
5.5.
Now there are options where you can set authentication and other options.
I'm not going to do that.
I'm simply going to create the virtual link so Roorda SPF 1 area 1 the virtual link and the right I.D.
that will connect to on this side is 3 to 3 2 or 3 2 or 3.
So show IP or SPF neighbor you can see that a neighbor relationship was established using virtual link
0 we can see that over here.
No election takes place on a virtual link show IP or SPF neighbor on the side we can see something similar
a neighbor relationship has been formed from Brother 3 directly to RADA 5 through the 0 SPF virtual
link.
So logically it's as if these two riders rather three and Rod of five are connected to one another so
Ken wrote a three paying the loop back of wrote a six.
Notice the raft is in the writing table so that looks better and notice a rather three can ping the
loot back of a a six.
And if we go back to write a one write a one can now ping the loop back of wrought a six and when we
do a trace notice it goes to Rod to Rod a three right a four rod of five and wrote a six.
This tunnel is not like a Geo re tunnel it's a no SPF mechanism so traffic still goes via the physical
links and you see every hop in the network which you wouldn't see if you were using Jari the virtual
link is simply used for SPF link advertisements.
So in other words to advertise Roth's so we've now solved the problem.
We've been able to configure the network to allow Rod one to ping brought us six let's have a look at
some more information on router 3 so show IP rot we are learning about that network as an into area
network.
It's coming from a separate area show IP SPF database for area zero.
Notice we have wrought a two rather three and root of five in area zero rather five is shown as DNA.
The neighbour relationship will not age so do not age this neighbour relationship because it's set through
a virtual link so we see rudder link states or LSA type one's net link states or LSA type 2s.
We see summary LSD or LSA type 3s we see something similar for Area 1 and we see external rots in the
0 SPF database
so that was an example of how to configure or SPF of virtual links to solve a problem where you've got
an area separated by a another area which is not area zero you know SPF.
All areas have to touch the backbone area.
In other words area zero.
So here we are extending area zero across Area 1 to meet the OSP f design criteria.
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