Our next topic is oh, SPF areas and O S P f l s a types
now, always VF, as I mentioned earlier breaks a large topology and I've drawn, not drawn out our little network Archer Apology on the board
into smaller, easier to configure sections. Call called areas.
So over here between router 123 and four, we have areas. Zero. This is rather one.
So between router one router to rather three and rather four on this land, we have area zero. Area zero is the backbone area.
Meaning you must have area zero to run. Oh, SPF
and all other areas must be directly connected to area zero. Which means all inter area traffic must flow through area zero.
So, you see, I have area one between router one and router to one. And I have area 51 between voter to and switch
eight or behind. Router to I have area 51.
Any traffic between area 51 area one has to pass through area zero. If I did not community areas, you know, and for example, I made this area 10 and there was no air Area zero inter area traffic would fail.
So all traffic must pass through area zero, which is the backbone to make it to another area.
A router that borders area zero and another area is called an area of order router or an A B R.
Once again, a router that borders to areas.
One of them has to be area zero. So a router bordering area zero and another area is called an area border outer. In this case, we have router to and rather one as our area of border routers.
Now, let's say a router to a one, for
just this discussion sake was connected to the Internet. So a router that takes us out of our network to another network is called and A S B R or an autonomous system boundary router.
A router that connects your network to an external network is called an autonomous system boundary router.
Now let's say we have
Well, we can look at Router three and router for here,
Router three and Router four. Since the only existing area zero are going to be called the area internal routers. So their internal to just one area
coming over here to Elsa types
they are Five different types of Ellis is that are relevant to your C, C and course there are others, but you don't need to know them right now.
The 1st 1 is your outer l A c
Every router in in an O SPF topology
produces one router. L s a
the router. L s a is the l s A. I described initially
when I started the SPF lecture. The router l essay describes the router links
the networks I p networks connected to those links
the neighboring routers and the metric to those routers
or the cost of the link to those routers.
The 2nd 1 is the network L S E.
The network Ellis is only produced by the D. R
so it will only be produced
on multi access links like Ethernet and the d R will produce one network. L s A. To describe
the i p address of the network and all the attacks routers and older attaching routers by their outer ID's.
So the Network L essay describes the network with its I P address
and all the routers connected to that network by their outer ID's on the network. L s is only produced by the D. R of the network.
Next comes the network summary Jealousy, the network summary. Elsa is produced by a bee. Ours, remember a be ours. Our routers that border area zero and another area
in our topology router one and router to are going to be a be ours.
Now, the networks Emery Elsa takes the network from one area of the I P network from one area and injects it into another area, and vice versa.
So Router One will produce a network summary, Elsa for area zero and injected into area one
and produce the network Somebody else a four area one and injected into area zero. So remember the originating router for a network summary L s A has to be an A B r or an area border router.
The 4th 1 is an autonomous system boundary Router Summary. L s a
The S B r summary Elsa is again produced
Well, for the years, we are some real estate. We would have to say that our Internet connection is not here
is less for 10. Our internet connection is on router three. Router tree now becomes autonomous system Boundary router or S V. R
now and is beer summary. LSD basically points to the location of the SBR, which is on Router three and is We are Somebody else's are also produced by
E be ours or area boater routers and injected into non backbone areas or non transit areas. Since Area 51 area one do not have other areas connected somewhere behind router to a one. These are non transit areas,
so and is we are summary Ellis say it points to the location off Router three or Router three's a router I D. And entry is injected by the A B ours router to and rather one into non transit areas to let routers away here know where the SBR is.
Lastly, the external Elsa
the external l s A actually carries all the networks that are external to euro SPF domain. So all the networks on the Internet
you would hope you would not import the whole Internet routing table into euro SPF. But selected networks
went out or three injects those networks into
the SPF dome in and will do so using an external L. S A.
This concludes our area and l s a lecture. Now we move on to the lab