Frame Relay inverse arp

[Darren Candlish]

Hi All,

I've a home lab which consists of three 2610xm routers and I have configured two routers back to back with FR subinterfaces. The commands are used are;

R1

frame relay switching

int s0/0

encap FR

no sh

clock rate 64000

frame-relay intf-type dce

int s0/0.1 point to point

ip add 192.168.4.1 255.255.255.252

frame-relay interface-dlci 101

R2

int s0/0

encap FR

no sh

cl ra 64000

int s0/0.1

ip add 192.168.4.2 255.255.255.252

frame-relay interface dlci 101

Everything works great with this config and I know how to configure without lmi too. My question is more for the CCNA exam and fill the gaps in so to speak. The question is when you configure FR with static mappings and inverse arp do you need actual frame relay switches on the other side of the link or can I configure on my home labs routers. I know I am gonna try and configure this as well, but can I configure multipoint on my third router with a different physical interface. Like R1 with s0/0 to R2 s0/0 and R1 s0/1 to R3 s0/0 with subinterfaces. Any feedback is much appreciated it thank you. 

[Peter Paluch]

Hi Darren,

when you configure FR  with static mappings and inverse arp do you need actual frame relay  switches on the other side of the link or can I configure on my home  labs routers. I know I am gonna try and configure this as well, but can I  configure multipoint on my third router with a different physical  interface. Like R1 with s0/0 to R2 s0/0 and R1 s0/1 to R3 s0/0 with  subinterfaces

It can be configured as you suggested but it will not be a true Frame Relay multipoint configuration. When speaking about multipoint connection, you are referring to the ability to reach several neighbors through the same interface, and have them all in the same identical IP subnet. Note that your suggested configuration uses different interfaces to allow R1 to speak to both R2 and R3, which is not multipoint by itself. Also, because of multiple interfaces, your three routers are not going to be interconnected by a single IP subnet.

So, if you want to create a true multipoint interconnection between your three routers so that each can potentially reach the other two via the same serial interface, and thus have all three routers in the same IP subnet, you would need a FR switch indeed.

Please feel welcome to ask further!

Best regards,

Peter

[Darren Candlish]

Hi Peter,

Thank you for answering my question. I configured the multipoint configuration as I suggested and funny enough the FR worked with the same dlci number. I got lmi through and the data link layer seemed to be working fine, but I couldn't ping between devices. You just reminded me that I broke the first rule of routing because I configured different physical interfaces with the same subnet doh. I am glad I made the mistake on my lab and not on the exam. Just when you think you have everything nailed down. I understand now that static mappings is prefered over dynamic and you would always connect to a FR switch from a ISP and not use a cisco router as a switch. Thanks for your response.