08-25-2009 10:56 PM - edited 03-06-2019 07:25 AM
Hi every body.
I have this scenario and possible solution :
There are one main side,R1 and two sides, R2 and R3 . Main side R1 is connected to both sides using frame relay in hub and spoke topology.
R1 is connected to frame relay network by s0. R1 and R3 are connected to Frame relay network by sub interfaces point-to point type s0/0.2 and s0/0.3 respectively.
1) Will R2 map the dlci 1 to int s0/0.2?
Here is my understanding, as soon as link between frame relay switch and s0 int of R2 comes up, R2 learns Vc is up and using dlci 2. Since this is only dlci R2 receives from FR switch and there is only one frame relay enabled int s0/0.2, R2 simply concludes this dlci is for int s0/0.2.
Had there been more than two or more dlci on R2 and more than one sun interface point-to-point type, then we would have needed to tell R2 which dlci is for which interface by using the command:
frame-relay interface-dlci
Is my understanding correct?
=========================================
For my second question, please consider the following with the same above mentioned topology in mind.
R1 config
int s0
10.10.10.1/24
frame-relay encapsulation
R2 config
int s0
frame-relay encapsulation
int s0/0.2 point-to-point
ip address 10.10.10.2/24
R3:
int s0
encapsulation frame-relay
int s0/0.3 point-to-point
10.10.10.3/24
==========================
On R1
Vc between R1 and R2 uses dlci dlci 2
Vc between R1 and R3 uses dlci 3
On R2
vc between R2 and R1 uses dlci 1
On R3
Vc between R3 and R1 uses dlci 1
Please note that there is no vc running between R2 and R3.
If i use the command on R2 " ping 10.10.10.3" , it should work. Below are my reasons:
1) When i issue the command ping 10.10.10.3, it matches the entry in routing table at R2
C 10.10.10.0/24 directly connected,s0/0.2
R2 finds the s0/0.2 is sub interface of point-to-point type, therefore only one vc or Dlci is expected on this interface.
Since R2 has dlci 1 on s0/0.2, therefore R2 simply uses this dlci and forwards this ping packet to R1 which in turn forwards it to R3.
Is my understaning correct?
thanks a lot.
Solved! Go to Solution.
08-25-2009 11:06 PM
Hello Sarah,
frame-relay interface-dlci is needed to be able to associate a DLCI to a specific subinterface otherwise the router can learn from LMI of the existence of the DLCI but it cannot associate it to the correct subinterface.
So I don't think it works also the second scenario.
Here you hit a different aspect:
Inverse ARP can handle the OSI L3 resolution problem but it cannot handle the DLCI to subinterface association.
This needs an explicit configuration on the router or all DLCIs will be associated to main interface (I guess)
Hope to help
Giuseppe
08-25-2009 11:14 PM
Yes it does work pretty much like you describe.
You dont need manual mapping on R1, it will find it from inverse-arp.
And yes, then R2 can ping R3 via R1.
One need you need on R2 and R3 is to tell them which DLCI you use as I mentioned in my previous post, the command is:
frame-relay interface-dlci 1
08-25-2009 11:16 PM
I just tested it, you need the frame-relay interface-dlci only on R2 and R3. And then it does work in the second scenario.
08-26-2009 10:58 AM
You are correct Sarah.
With inverse arp disabled it works as described as it's point to point.
Here is an output from the router:
R1#show frame map
Serial0/0/0.1 (up): point-to-point dlci, dlci 102(0x66,0x1860), broadcast
status defined, active
And the debug when a ping goes:
*Aug 26 18:54:32.392: Serial0/0/0.1(o): dlci 102(0x1861), pkt type 0x800(IP), datagramsize 104
*Aug 26 18:54:32.448: Serial0/0/0(i): dlci 102(0x1861), pkt type 0x800, datagramsize 104
*Aug 26 18:54:32.452: ICMP: echo reply rcvd, src 10.0.0.2, dst 10.0.0.1
*Aug 26 18:54:32.452: Serial0/0/0.1(o): dlci 102(0x1861), pkt type 0x800(IP), datagramsize 104
*Aug 26 18:54:32.508: Serial0/0/0(i): dlci 102(0x1861), pkt type 0x800, datagramsize 104
*Aug 26 18:54:32.508: ICMP: echo reply rcvd, src 10.0.0.2, dst 10.0.0.1
*Aug 26 18:54:32.508: Serial0/0/0.1(o): dlci 102(0x1861), pkt type 0x800(IP), datagramsize 104
*Aug 26 18:54:32.564: Serial0/0/0(i): dlci 102(0x1861), pkt type 0x800, datagramsize 104
*Aug 26 18:54:32.564: ICMP: echo reply rcvd, src 10.0.0.2, dst 10.0.0.1
*Aug 26 18:54:32.568: Serial0/0/0.1(o): dlci 102(0x1861), pkt type 0x800(IP), datagramsize 104
*Aug 26 18:54:32.624: Serial0/0/0(i): dlci 102(0x1861), pkt type 0x800, datagramsize 104
*Aug 26 18:54:32.624: ICMP: echo reply rcvd, src 10.0.0.2, dst 10.0.0.1
*Aug 26 18:54:32.624: Serial0/0/0.1(o): dlci 102(0x1861), pkt type 0x800(IP), datagramsize 104
*Aug 26 18:54:32.680: Serial0/0/0(i): dlci 102(0x1861), pkt type 0x800, datagramsize 104
08-25-2009 11:06 PM
Hello Sarah,
frame-relay interface-dlci is needed to be able to associate a DLCI to a specific subinterface otherwise the router can learn from LMI of the existence of the DLCI but it cannot associate it to the correct subinterface.
So I don't think it works also the second scenario.
Here you hit a different aspect:
Inverse ARP can handle the OSI L3 resolution problem but it cannot handle the DLCI to subinterface association.
This needs an explicit configuration on the router or all DLCIs will be associated to main interface (I guess)
Hope to help
Giuseppe
08-25-2009 11:16 PM
I just tested it, you need the frame-relay interface-dlci only on R2 and R3. And then it does work in the second scenario.
08-25-2009 11:14 PM
Yes it does work pretty much like you describe.
You dont need manual mapping on R1, it will find it from inverse-arp.
And yes, then R2 can ping R3 via R1.
One need you need on R2 and R3 is to tell them which DLCI you use as I mentioned in my previous post, the command is:
frame-relay interface-dlci 1
08-26-2009 12:03 AM
Thanks Lucien
My understanding is we don't need inverse arp on sub int ptp. Because there is only one dlci mapped to the interface.
For example in my earlier post, i described a topology.
If i use the command ping 10.10.10.3 on R2, r2 will match it to entry;
C 10.10.10.0/24 directly connected s0/0.2
Next R2 checks which dlci is used on s0/0.2 which is dlci 1
R2 simply sends the ping packet using dlci 1 to R1 which then forwards it to R3.
So i don't see any reason to have inverse arp enabled on s0/0.2 on R2 for ping 10.10.10.3 to work.
Thanks and have a nice day.
08-26-2009 10:58 AM
You are correct Sarah.
With inverse arp disabled it works as described as it's point to point.
Here is an output from the router:
R1#show frame map
Serial0/0/0.1 (up): point-to-point dlci, dlci 102(0x66,0x1860), broadcast
status defined, active
And the debug when a ping goes:
*Aug 26 18:54:32.392: Serial0/0/0.1(o): dlci 102(0x1861), pkt type 0x800(IP), datagramsize 104
*Aug 26 18:54:32.448: Serial0/0/0(i): dlci 102(0x1861), pkt type 0x800, datagramsize 104
*Aug 26 18:54:32.452: ICMP: echo reply rcvd, src 10.0.0.2, dst 10.0.0.1
*Aug 26 18:54:32.452: Serial0/0/0.1(o): dlci 102(0x1861), pkt type 0x800(IP), datagramsize 104
*Aug 26 18:54:32.508: Serial0/0/0(i): dlci 102(0x1861), pkt type 0x800, datagramsize 104
*Aug 26 18:54:32.508: ICMP: echo reply rcvd, src 10.0.0.2, dst 10.0.0.1
*Aug 26 18:54:32.508: Serial0/0/0.1(o): dlci 102(0x1861), pkt type 0x800(IP), datagramsize 104
*Aug 26 18:54:32.564: Serial0/0/0(i): dlci 102(0x1861), pkt type 0x800, datagramsize 104
*Aug 26 18:54:32.564: ICMP: echo reply rcvd, src 10.0.0.2, dst 10.0.0.1
*Aug 26 18:54:32.568: Serial0/0/0.1(o): dlci 102(0x1861), pkt type 0x800(IP), datagramsize 104
*Aug 26 18:54:32.624: Serial0/0/0(i): dlci 102(0x1861), pkt type 0x800, datagramsize 104
*Aug 26 18:54:32.624: ICMP: echo reply rcvd, src 10.0.0.2, dst 10.0.0.1
*Aug 26 18:54:32.624: Serial0/0/0.1(o): dlci 102(0x1861), pkt type 0x800(IP), datagramsize 104
*Aug 26 18:54:32.680: Serial0/0/0(i): dlci 102(0x1861), pkt type 0x800, datagramsize 104
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