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Frame-realy...MAP or Interface-dlci????
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| I have been using the frame-relay interface-dlci command for my configurations of 50+ routers (mostly 1600s and 2500s).
I see you can also use the frame-relay map command.
As far as I understand it you use the DLCI command on a point-to-point frame, and the map on a point-to-multipoint frame.
Question: What is the difference between point-to-point frame and point-to-multipoint frame?
Is map command better or is DLCI command more appropriate?
I'm just confused right now and would appreciate it if somebody could set me right.
thanks in advance. | |
| MadChef 2002-02-01, 5:25 am |
| A point to point is a logical point to point network; there's only one other host on it. It's sort of a one to one relationship if that makes sense. Point to multipoint is more like a one to many relationship. There's the possibility of having many other hosts on that network and sub inteface. It's also like configuring FR with no sub interfaces.
It's also important to note that you don't HAVE to use a frame map statement on multipoint interfaces. The point of the map statements is to map the layer three address with the layer two address (the dlci). If you had a sub int addressed as 192.168.1.0/24, a map statement would tell the router that on that particular multipoint interface it would dlci 301 to get to .1 and 302 to get to .2, for example. Frame relay inverse arp can be used to achieve those mappings on a dynamic basis, if you like living on the edge and can give up that control. There's no need for this mapping with a point to point sub interface because the router knows that there's only one dlci configured on the interface and there can be only one other end of that interface. So anything on that network just gets sent out that PVC without a need to map a particular address to a particular dlci.
There's no real question as to which command is appropriate since they're used in different situations. The question is really which topology is more appropriate and that depends on your particular situation. Ever since it became available in IOS, most people choose to use point to point since it overcomes the difficulties with split horizen and NBMA that you find with configuring FR on an interface or multipoint interface.
That's my take on it. I'm sure someone will correct me if I misspoke. Let us know if you have other questions.
MadChef | |
| Yankee 2002-02-02, 6:47 am |
| When I first saw this question I was going to point iso to the Caslow book because this involves such a complicated answer, but since MadChef (ya can tell he's been doing some CCIE studying!) did a pretty complete job I figured I would chime in too.
In an physical interface to physical interface config inverse arp dynamically maps the dlci to ip address well. The problem comes in the hub to spoke design where the physical interface on the hub hosts many dlcis and the spoke hosts only one. If you do not statically map with this design, each spoke will be able to communicate with the hub, but spoke to spoke communication fails. The solution is to add the map command for each spoke dlci on each spoke router. Nothing needs to be done on the hub. You can see where this configuration can be cumbersome and difficult to maintain, so we use subinterfaces point to point on both the hub and the spoke with the dlci command to avoid this problem and keep the config as simple as possible.
Hope that helps too,
Yankee | |
| MadChef 2002-02-02, 9:01 am |
| quote:
Originally posted by Yankee
MadChef (ya can tell he's been doing some CCIE studying!)
Only 39 days till the lab. I decided not to put it off....
You're right, Caslow does an excellent job of explaining the ramifications of FR as an NBMA technology and how it affects routing. So if you want to read more iso, get Caslow.
This was posted while doing a practice lab that, incidentally, involves configuring OSPF with FR on point-to-point and multipoint sub interfaces mixed with FR on physical interfaces. Yippee.
MadChef | |
| Yankee 2002-02-02, 9:30 am |
| You'll do just fine on the lab, MC and I'll be waiting for a private message with your number in 40 days 
Are you taking one of Caslow's classes before the lab? I'm trying to decide if it's worth the money. My boss is taking one in a couple of weeks so I'll know more then.
Yankee | |
| MadChef 2002-02-02, 8:36 pm |
| quote:
Originally posted by Yankee
Are you taking one of Caslow's classes before the lab? I'm trying to decide if it's worth the money. My boss is taking one in a couple of weeks so I'll know more then.
No, I'm not. One of my co-workers did and he really got a lot out of it. Course he also hasn't taken the lab yet.
MC |
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