Frame Relay and subinterface and Multipoint

zillah

Single physical interface can have two logical subinterfaces.

Also we can have multiple PVCs per physical interface or per logical subinterface on a router.

Configuring a multipoint interface (physical) or a multipoint subinterface (logical), allows one interface or subinterface to be associated with more than one DLCIs.

When interface or subinterface associated with more than one DLCIs,,,Does it still consider as point-to-point or multipoint ?

keenon

zillah wrote:

Single physical interface can have two logical subinterfaces.

Also we can have multiple PVCs per physical interface or per logical subinterface on a router.

Configuring a multipoint interface (physical) or a multipoint subinterface (logical), allows one interface or subinterface to be associated with more than one DLCIs.

When interface or subinterface associated with more than one DLCIs,,,Does it still consider as point-to-point or multipoint ?

to answer question 1 you can have as many as you want

answer 2 is multiple per physical interface,1 on each logical (sub)interfaces

zillah

1 on each logical (sub)interfaces

What does 1 mean ?

keenon

one

zillah

answer 2 is multiple per physical interface,1 on each logical (sub)interfaces

Sory,,,my understanding to what you said that the configuration should be:

multipoint for physiacl interface.

point-to-point for subinterface.

Am I right ?

EdTheLad

By default when you configure a serial port with FR encapsulation this interface will be multipoint.You can configure multiple dlci's on this interface but all devices connected must be on the same subnet.
This config can cause problems with routing protocols due to split horizon
and broadcasts so cisco developed the subinterface as a workaround.
You can configure multiple subinterfaces on each serial port and you can
choose what type the subinterface is i.e. ptp or multipoint.
The multipoint subinterface will work with exactly the same behaviour as if it was the serial interface, the point to point will work a little different with
routing protocols.

zillah wrote:

Also we can have multiple PVCs per physical interface or per logical subinterface on a router.

Yes, you can have multiple pvc's per physical interface,generally you wont configure these, as the LMI should detect them from the attacted FR switch.On the subinterface, if its ptp you have one dlci, if its multipoint you can have numerous but as stated generally you wont configure as automatically detected.All you need to do is configure your encapsulation and IP address and everything else should be dynamic, LMI will detect available dlci's, inverse ARP will learn which IP addresses map to which dlci's

zillah wrote:

When interface or subinterface associated with more than one DLCIs,,,Does it still consider as point-to-point or multipoint ?

It makes no sense to configure a ptp subinterface with more than one dlci,
this subinterface is connected to a single end device, it is not part of a nbma network so therefore only one dlci is required.A serial port is always multipoint,a subinterface is either as explained above!

zillah

Thanks ed_the_lad for that. I was looking for this:

It makes no sense to configure a ptp subinterface with more than one dlci

See my discussion here and let me know if you agree with the guy that he replied....(see the link below same question)

http://www.broadbandreports.com/forum/remark,14802925

EdTheLad

aryoba wrote:

I understand you are talking about Multipoint. As I previously mentioned, usually the big pipe (that was "configured as Multipoint") has multiple subinterfaces which each subinterface go to specific remote Frame Relay with specific PVC value as point-to-point connection. In other words, the big pipe multipoint was configured as multiple independent point-to-point subinterfaces.

He's calling the serial interface the big pipe,after you create subinterfaces
the big pipe really doesnt exist anymore.The subinterfaces can be configured as either ptp or multipoint.

aryoba wrote:

The network design is hub and spoke (point to multipoint) where the big pipe of T3 or E3 is configured as "multipoint" and the smaller pipe T1 or E1 is configured as "single point" (or just point).

Normally the E3 would be configured with multiple subinterfaces,these subinterfaces generally will be ptp i.e. each subinterface will have a different ip subnet address.
You could also create a multipoint subinterface which means remote devices must be on the same ip subnet.

aryoba wrote:

However each of the branches see the headquarter as point-to-point connection. At the same time, the headquarter sees branches as multipoint-to-point connection. This is possible due to the big pipe of T3 or E3 is usually configured as multiple single point-to-point connections to each branches with specific PVC values.

Depending on how you configure the branches influences on how the branches see the headquathers.You could configure the branches multipoint which means they see the headquarters as multipoint and the same goes for ptp.These settings ptp and multipoint are local settings and have no influence on the remote side.The main thing you need to realise is that when a port is configured multipoint it is considered to be a nbma network.This multipoint port can have multiple dlci's but all remote devices connected to these dlci's must be on the same logical subnet.
When you create a ptp interface this behaviour is just like a ptp serial interface.You select a unique ip address and the remote side must be on the same subnet.The difference is that you can create multiple subinterfaces and hence one FR serial interface can have multiple IP networks.
It's your choice how to configure the remote devices, it all depends on exactly what you require.If this was the only connect to this remote device you dont need a subinterface.It's best practice however to create subinterfaces as this gives you scalability incase you want to add another
subnet in the future.In the example you gave the remote devices can be configured either ptp or multipoint either will work.

zillah wrote:

1- I have to configure interface 0/0 for both RTC and RTB in the link above as point-to-ponit,,,,Am I right ?

You can configure the interfaces either ptp or multipoint once they
are on the same subnet as the desintaion endpoint,both will work.However in this example i would create a subinterface and configure it ptp.

zillah wrote:

2- I have to configure subinterface 0/0.1 for RTA as multipoint.

Yes,because as you can see RTA,RTB,RTC are all on the same IP network.

zillah wrote:

3- Subintercae 0/0.1 on RTA has got two DLCIs, which mean it has got two PVC,,,,Am I right ?

Correct

zillah wrote:

4- Right now on RTA we have two subinterfaces (0/0.1 and 0/0.2).

Suppose we have 3 subinterfaces on RTA (0/0.1, 0/0.2, 0.03) 0/0.1 to RTC and 0/0.3 to RTB and 0/0.2 to RTD,,,----in this scenario still we have to configure each interface (not subinterface) on RTB and RTC and RTD as point-to-point,,,and each subinterafeces (not interface) on RTA as point-to-point as well ,,,Am I right ? What is the difference between these two scenario

If you had 3 subinterfaces on RTA, this would mean that each remote device is configured on a different IP subnet.The subinterfaces on either end could be ptp or multipoint depending on exactly what you want.
In this case since the remote device only needs to connect with RTA, i would config a ptp subinterface.If however the remote device needed to connect to both RTA and another branch router on the same IP subnet i would configure a multipoint subinterface.If the remote device need to connect to RTA and another branch router on different IP networks i would create multiple ptp subinterfaces.

Remember when creating your FR network a routing protocol will probably be running on top of it so the choice you make about ptp and multipoint will have an effect on your routing protocol.

zillah

Thanks ed_the_lad for this effort