Frame Relay

Ok I think i found my biggest point of confusion on the CCNA track.. and its frame relay (not a big shocker there)

I am trying to make my own frame relay lab based off of what the technotes is but i get kinda confused

It seems the first thing I dont understand is the frame relay maps.. so if someone can clarify that, that would be very helpful.

2nd. I thought that you had to use subinterfaces for frame relay?

I know point to point is used for routers on different subnets and point to multipoint is used for routers on the same subnet

http://www.techexams.net/techlabs/ccna/lab_fr.shtml is the link to the technote lab

I just am so confused now.. my setup was going to be 3 routers - 2 routers on diff subnets and one router in the middle as the frame switch.

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Comments

networker050184

You can do frame relay on sub interfaces or physical interfaces. If you put the two end routers on different subnets they will not form an adjaceny. So your two end routers need to have their interfaces on the same subnet. You use the frame relay maps to map the ip address to the dlci for example when you are not using inverse arp.

Netstudent

In addition, the map statement maps the local DLCI to the remote IP. So if you had:

RouterA(DLCI101)

RouterB(dlci102)

RouterA = 192.168.1.1
RouterB = 192.168.1.2

If I-ARP is turned off and you must use the map command, then on RouterA it would be:

frame-relay map ip 192.168.1.2 101 broadcast

And on RouterB the map statement would be:

frame-relay map ip 192.168.1.1 102 broadcast

One more thing that I have found with my gear is that when you use the physical interface only, you can let the interfaces learn of their DLCI's through LMI's coming from the switch. You do not necesarily have to nail down the DLCI on the interface. However if you use subinterfaces, I think you have to use the frame-relay interface-dlci command to nail down the DLCI. If you do not manually put them on the subinterface, then the router will hear the LMI's and start putting all the DLCI's on the physical interface intead of the subinetrface that you want.

Plazma

what about on point to point? Like it appears the frame switch 'router' is configued as point to multipoint as all interfaces/routers have an ip in the same subnet.

is it possible to setup a router/frame switch to do point to point on each interface?

Netstudent

That is not the definition of a multipoint interface. The definition of multipoint is having multiple VC's terminate at that interface. You only have one single p-t-p VC. But you are right that multipoint interfaces will be in the same subnet, but thats the wrong way of looking at it because as you see p-t-p interfaces share a subnet as well.

Plazma

I think i understand it now

each dlci map is like a direct connection to another router, it just goes through the frame switch or router.

if inverse arp is enabled on the frame switch, all you have to do is is setup the mappings on the frame switch

if inverse arp is NOT enabled, you have to setup the mappings on the frame switch AND setup dlci to ip address mapping (similar to setting up static routes)

Netstudent

Plazma wrote:

I think i understand it now

each dlci map is like a direct connection to another router, it just goes through the frame switch or router.

if inverse arp is enabled on the frame switch, all you have to do is is setup the mappings on the frame switch

if inverse arp is NOT enabled, you have to setup the mappings on the frame switch AND setup dlci to ip address mapping (similar to setting up static routes)

Inverse ARP is sent by the endpoint routers, not the switch. If IARP is enabled on the endpoints then you do not need to use map commands on the enpoints. Mapping statements are also configured on the endpoint router, not the switch. Frame-relay routes are configured on the switch.

Plazma

Netstudent wrote:

Plazma wrote:

I think i understand it now

each dlci map is like a direct connection to another router, it just goes through the frame switch or router.

if inverse arp is enabled on the frame switch, all you have to do is is setup the mappings on the frame switch

if inverse arp is NOT enabled, you have to setup the mappings on the frame switch AND setup dlci to ip address mapping (similar to setting up static routes)

Inverse ARP is sent by the endpoint routers, not the switch. If IARP is enabled on the endpoints then you do not need to use map commands on the enpoints. Mapping statements are also configured on the endpoint router, not the switch. Frame-relay routes are configured on the switch.

I get it now.. i was getting my mapping and frame relay route statements mixed up. The frame relay switch si just the 'middle man' that kinda handles the connections from one DLCI to the next