| Author |
I want to clear a few things up about Frame Relay
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| Boulware5 2004-02-18, 11:11 pm |
| Just a few things I'm not totally clear on that I can use some more explaining. This is how I understand it from reading our text book...
1. If the remote router supports Inverse ARP, you don't need to map an IP to a DLCI number, right?
2. A point-to-point Frame Relay connection consists of remote routers on different subnets. Is this correct? And point-to-point connections do not support Inverse ARP, so is that when you have to statically enter them? | |
| worrywarm 2004-02-19, 12:28 am |
| quote:
Originally posted by Boulware5
Just a few things I'm not totally clear on that I can use some more explaining. This is how I understand it from reading our text book...
1. If the remote router supports Inverse ARP, you don't need to map an IP to a DLCI number, right?
2. A point-to-point Frame Relay connection consists of remote routers on different subnets. Is this correct? And point-to-point connections do not support Inverse ARP, so is that when you have to statically enter them?
1. right. | |
| worrywarm 2004-02-19, 12:37 am |
| 2. what you mean point-to-point is the topology or the subinterface type? I don't see any book say that either of them doesn't support IARP?? | |
| Boulware5 2004-02-19, 12:52 am |
| Ok well, the book my class is using is the Course technology CCNA guide to CISCO networks. They several times refer to Frame Relay setups as either point-to-point and multipoint. In it, it says p-to-p connections do not support inverse arp because there is one path available.
What I don't get is the difference between a multipoint and a point-to-point connection. In the diagrams both the p-to-p and multipoint connections have multiple paths. It kind of hints that a point-to-point configuration is where all remote routers are on different subnets. Is this basically the definition of p-to-p configs? | |
| Yankee 2004-02-19, 4:29 am |
| A multipoint frame-relay hub router will use a single physical serial interface with one ip address and mask assigned. This interface can be connected to many remote sites on the same address block assigned (network).
A point-to-point frame-relay hub router will use a single physical serial interface with one or more virtual subinterfaces created. Each subinterface will have its own network assigned and be connected to only one remote site, thus the term point-to-point.
Hope that helps a little,
Yankee | |
| worrywarm 2004-02-19, 10:47 am |
| Yankee's expalanation is exactly accurate. However, in the case of p-t-p subinterface, you still can use IARP, in this case,
The frame-relay interface-dlci command uses dynamic resolution with inverse ARP. If you can¡¯t use inverse ARP, or don¡¯t want to, then use the framerelay map command on the subinterface to perform manual resolution, like this:
Router(config)# interface serial [ slot_#/] port_#. subinterface_#
point-to-point|multipoint
Router(config-if)# frame-relay map protocol_name
destination_address local_dlci_#
[broadcast] [ietf|cisco]
As an example of the configuration,
RouterA(config)# interface serial 0
RouterA(config-if)# encaspulation frame-relay ietf
RouterA(config-if)# no shutdown
RouterA(config-if)# exit
RouterA(config)# interface serial0.1 point-to-point
RouterA(config-subif)# ip address 192.168.1.1 255.255.255.0
RouterA(config-subif)# frame-relay interface-dlci 101
RouterA(config-subif)# exit
RouterA(config)# interface serial0.2 point-to-point
RouterA(config-subif)# frame-relay interface-dlci 201
RouterA(config-subif)# ip address 192.168.2.1 255.255.255.0
...
Can you explain a little bit more of the reason that IARP not working in P-t-P if you still believe so?
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| Boulware5 2004-02-19, 1:32 pm |
| quote:
Originally posted by worrywarm
Can you explain a little bit more of the reason that IARP not working in P-t-P if you still believe so?
Well because my book clearly states that. I guess they are wrong!
Also, a multipoint connection CANNOT have virtual subinterfaces? In my book it shows diagrams of multipoint connections WITH subinterfaces (each subinterface with a different IP). | |
| worrywarm 2004-02-19, 2:15 pm |
| quote:
Originally posted by Boulware5
Well because my book clearly states that. I guess they are wrong!
Also, a multipoint connection CANNOT have virtual subinterfaces? In my book it shows diagrams of multipoint connections WITH subinterfaces (each subinterface with a different IP).
surely a multipoint connection can have virtual subinterfaces, pls see the following example, itoffers an example of using multipoint subinterfaces on a router to set up Frame Relay connections.
RouterA(config)# interface serial 0
RouterA(config-if)# encaspulation frame-relay ietf
RouterA(config-if)# no shutdown
RouterA(config-if)# exit
RouterA(config)# interface serial0.1 multipoint
RouterA(config-subif)# ip address 192.168.1.1 255.255.255.0
RouterA(config-subif)# frame-relay interface-dlci 101
RouterA(config-subif)# frame-relay interface-dlci 102
Notice that in a multipoint connection it's one subinterface with multiple local dlci connects with different serial or subinterfaces on different routers(all of them in the same subnet though). In the case of p-to-p, it's one phsical port to another physical port or one subinterface to another subinterface(only these two use same subnet)
Hope I made myself clear | |
| Boulware5 2004-02-19, 2:28 pm |
| Ok I think I got it. The book is slightly misleading and apparently blatantly wrong when it says IARP can't be used with p-to-p. Maybe the book means that IARP isn't on by DEFAULT on multipoint configs and you have to somehow enable it?
Anyway, I can see probably the major benefit of using a point-to-point config is that it allows you to use a single network for all your routers. | |
| worrywarm 2004-02-19, 3:37 pm |
| quote:
Originally posted by Boulware5
Ok I think I got it. The book is slightly misleading and apparently blatantly wrong when it says IARP can't be used with p-to-p. Maybe the book means that IARP isn't on by DEFAULT on multipoint configs and you have to somehow enable it?
IARP is enabled by default.
Anyway, I can see probably the major benefit of using a point-to-point config is that it allows you to use a single network for all your routers. [/QUOTE]
Point-to-multipoint allows you to use a single subnet for all your nodes in the nw.
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