When you are using frame relay on a physical interface or p2m subintf,
Map statement tells the router which PVC/DLCI to use when
sending packets to a destination ip address.
for example,
frame map ip 10.10.10.1 200
frame map ip 20.20.20.1 201
These statements tell the router that to send packets to
10.10.10.1, use the PVC that is configured for DLCI 200.
But,
To get to 20.20.20.1, this time, send the packet to the PVC that is
configured to 201.
These statements are there because unlike a true point to point serial
interface, you actually have multiple logical connections (PVCs) on this 1
physical interface. Because of this, you need to help the router
distinguish which PVC should be used to get to one of the many remote sites.
Now when you use a subinterface, what happens is that the router configures
a logical interface, under the physical interface that is treated like a
point to point serial link. In this type of of situation, you do not need
to do any map statements because, in theory, there can be only one remote
end router. Compared to when you just use the physical interface and have 5
PVCs terminated on the physical. The only additional thing you have to do
on the subintf is that you use the interface dlci xxx command under the p2p
subintf to tell it which DLCI this subintf belongs to.
If you want to do a comparison, we can use a common telephone.
you have 1 phone line coming into the house into 1 phone. Even though you
have only 1 phone/phone line(physical serial interface), by utilizing the
different phone numbers, you can call many different people because for each
diff phone number(DLCI), phone and the phone company will create a
logical/virtual connection(PVC) to the other phone...
so instead of saying frame map ip 10.10.10.1 200, we have
phone map john 555.1212
phone map bill 555.2525,
which means, to talk to john on the phone, use the number 555.1212
And later, what you do is just run a single line (p2p subintf) to john's
house direct and you run a single phone line to Bill's house direct. In
this situation, all you need to do is just mark (intf dlci xxx) somewhere on
the phone line which of the phone lines goes to john's and which one goes to
Bill's.
hope this helped and I did not ramble on stuff that did not make sense.
Paul
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=18928&t=18917
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