EIGRP over Frame-Relay

(Hussein Samir) #2

Hi Rene,

Can we use “frame-relay interface-dlci DLCI NUMBER” command in frame-relay multipoint connection ?

(Rene Molenaar) #3

You could yes, basically all the command does is say “this DLCI number belongs to this interface”.

(Hussein Samir) #4

So how dose the interface map between IP address and dlci number since we have tow router on the same subnet on the other side ?

(Rene Molenaar) #5

Inverse ARP will take care of that. If you use “frame-relay interface DLCI” on a multipoint sub-interface then it will work.

(Hussein Samir) #6

Thanks Rene,

Now it’s clear.

(husam s) #7

could you confirm if this include int he ccie v5 exam or not ! coz its linked with the ccie .

(Rene Molenaar) #8

Hi Husam,

I’ll remove it from the CCIE page, frame-relay is not in CCIE V5 anymore.

Rene

(Adam M) #9

Hi Rene,

I was just wondering, would there be any scenario where multi-point frame relay would be used? The only scenario I could think of is in a home broadband users router where they only need a default route pointing to an interface. They don’t really need to populate their routing tables like a multi-site business would.

(Rene Molenaar) #10

Hi Adam,

Frame-relay is a really old WAN protocol, you won’t see it much anymore.

Two possible scenarios I can think of are:

  1. A business with multiple sites that have to be connected in a full mesh.
  2. A business with a HQ and some remote sites that need connectivity to the HQ.

And for whatever reason, the requirement is to have a single subnet on the frame-relay network.

Frame-relay was never really used for home users. DSL and Cable are more popular.

Rene

(george m) #11

Hey Rene,

I have a quick question regarding the multipoint. I’ve copied the text for the multipoint.

I cannot see how in the configuration you are not specifying that this is a broadcast map and on the below output is show as one. Also the fact that it shows as dynamic, it should show as static?

R1(config)#interface serial 0/0.123 multipoint 
R1(config-subif)#ip address 192.168.123.1 255.255.255.0
R1(config-subif)#no ip split-horizon eigrp 123
R1(config-subif)#frame-relay interface-dlci 102 
R1(config-subif)#frame-relay interface-dlci 103

On the sub-interface we will configure the IP address and we will disable EIGRP split horizon. By default our DLCI numbers will be “attached” to the physical interface. Since we are now using a sub-interface we have to tell the router that the DLCI numbers belong to this sub-interface.

After making these changes you can verify that the frame-relay maps have been updated:

R1#show frame-relay map 
Serial0/0.123 (up): ip 192.168.123.2 dlci 102(0x66,0x1860), dynamic,
              broadcast,, status defined, active
Serial0/0.123 (up): ip 192.168.123.3 dlci 103(0x67,0x1870), dynamic,
              broadcast,, status defined, active
(oscar s) #12

In the text says:
You can choose between multipoint or point-to-point, let’s choose multipoint:

R1(config)#interface serial 0/0.123 multipoint 
R1(config-subif)#ip address 192.168.123.1 255.255.255.0
R1(config-subif)#no ip split-horizon eigrp 123
R1(config-subif)#frame-relay interface-dlci 102 
R1(config-subif)#frame-relay interface-dlci 103

but in previous post you mentioned that frame-relay interface dlci is for point-to point, and frame-relay map ip is for multipoint??

(Rene Molenaar) #13

@George

When we use the frame-relay interface-dlci command, we tell the router that the DLCI number belongs to this sub-interface. This allows inverse ARP to do its work and learn the mappings dynamically. By default, broadcast is enabled.

If you would configure frame-relay maps, that’s when you would see static entries.

@Oscar

On point-to-point interfaces, the only thing you’ll ever need is the frame-relay interface-dlci command since there is only one PVC on this sub-interface.

For point-to-multipoint, you will have to use the frame-relay map command if you want to explicitly configure which IP address is reachable on which PVC. The frame-relay interface-DLCI command will still work if you use Inverse ARP.

Rene

(MICHAEL P) #14

Rene,

I noticed in the frame-relay “eigrp on Multipoint Frame-Relay” you did not do the ping back to R3.
So, when I tried it failed of course. I created in GNS3 a loopback 3.3.3.3 on R3 and advertised it on
EIGRP and it would not ping from router 2(R2). You then have to correct the problem by mapping the DLCI on
router 3, as well. If you do not add the static DLCI mapping to the interface s0/0 on R3 the entire router
is not able to be pinged from R2 to R3. Checking the Routing table shows an EIGRP route (R2) through R1 but
R3 will not respond to the echo request. I scratched my head on that one for a while.

I like using the loopback 0 address for troubleshooting with ping as well. I am sure you were aware of that the
other R3 Static DLCI command was needed but us newbs are not so fortunate. You state that through static frame relay
mapping that adjacencies can be built between router 2 and 3. Can you elaborate on that? As well how would we build
redundancy into this scenario of hub and spoke. If something happens to PVC between either R2 or R3 and R1 then R3
cannot reach reach R2 and visa-versa. How do we map from R2 to R3 so redundancy is accomplished (partial-mesh). EIGRP would then
develop new routes for traffic between R2 and R3. More efficient and at a lower hops with the new adjacencies.

Can you elaborate on redundancy over frame relay and how we develop adjacencies through Frame relay mapping?
Thanks , this was extremely informative on Frame relay and EIGRP. :slight_smile:

thanks
Forrest

(Nirosh R) #15

Hi Rene

1)When there is frame relay connectivity between routers,why do we need EIGRP?

2)R2 know how to reach to R1 as there is PVC between them and R1 know how to reach R3, why cant R2 reply to R3’s ping.

Regards
Nirosh Reddy

(Rene Molenaar) #16

@Forrest That’s right, in that example I only solved the problem for the ping from R3 to R2 by adding a frame-relay map on R2. For the other way around, you should add a map on R3 as well.

The underlying problem here is that EIGRP expects the network to be multi-access, this means that all devices should be able to reach each other directly. In reality, only the hub can reach the spokes directly. You won’t be able to estalish an EIGRP adjacency between R2/R3 directly with only PVCs to the hub.

It’s better to use frame-relay point-to-point everywhere instead. You won’t have issues with split horizon and spoke-to-spoke connectivity.

Trying OSPF instead of EIGRP is also an option. Take a look at this example:

Depending on the OSPF network type, OSPF will use different IP addresses for the next hop which solves the missing frame-relay maps problem.

In the hub and spoke topology, the hub is always a single point of failure. You could solve this by adding a second hub. Two hubs routers on your main network, all spoke routers connected to both hubs. It’s similar to the DMVPN topology with two hubs:

@Nirosh you will need a routing protocol (like EIGRP) to advertise any networks BEHIND the hub or spoke routers. If there is no connectivity between two (spoke) routers, you will have to add some additional frame-relay maps.

Rene

(KONSTANTINOS T) #17

Hi,

My question is if we have to configure also the spoke routers with the same type of logical sub-interface that we use in the hub? In other examples, and I used it as well on GNS3, I configured my hub router with logical sub-interfaces (point-to-point)/(multi-point) but for the spoke routers I always used the physical interface regardless the setup on the hub router. Is this approach correct ? Thus my configuration on the spokes was always done with the "frame-relay map ip ", which I take into account both for the hub router and rest of spokes. Thus I use it as many times as necessary, and the difference is in the . However, in your examples, you use also sub-ifs on spokes, so to conclude what’s the correct approach for the spoke routers? Physical or logical sub-ifs ?

(Lazaros Agapides) #18

Hello Konstantinos!

The spoke routers can be configured to function using a subinterface or using the physical interface for both point to point configurations (each link between routers has its own subnet) or point to multipoint configurations (all routers are in the same subnet). It is a good idea however to use subinterfaces because the numbers used for the subinterface can correspond to the DLCIs of the PVC. It is also a more symmetric configuration having both ends configured in the same way. The functionality will be the same however.

I hope this has been helpful!

Laz

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(Olivier S) #19

Hi Rene,

please when configuring subinterfaces on frame Relay, do we have to configure the main physical interface with frame relay encapsulation and IP address before configuring the subinterfaces with
with different subnets?
thanks
Olivier

(Lazaros Agapides) #20

Hello Oliver

When configuring subinterfaces to function with Frame Relay, it is necessary to first configure the main physical interface with frame relay encapsulation. There is no need to configure an IP address as each subinterface will have its own IP address.

I hope this has been helpful!

Laz

(Olivier S) #21

Thanks Laz, that was really clear.

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