Configuring multipoint subinterface so the interface status reflects status of the PVC

On a physical frame-relay interface, if the opposite end goes down, the local interface will remain up/up. When using multipoint subinterfaces this is not the case. When the remote interface goes down (taking the dlci with it), the local ends puts its interface in a down/down state.

R1, R3 and R5 connect via full mesh frame-relay, subnet 190.1.135.0/24

R1 dlci 103 maps to R3 dlci 301
R1 dlci 105 maps to R5 dlci 501
R3 dlci 305 maps to R5 dlci 503

Configure all routers on the physical interfaces.

Here is the outlook so far from R3:

R3#show ip int brief serial 1/0
Interface IP-Address OK? Method Status Protocol
Serial1/0 190.1.135.1 YES manual up up
R3#

Now Let's shut the physical interfaces On R5 and R1:

R5(config)#int s0/0
R5(config-if)#shut

R1(config)#int s0/0
R1(config-if)#shut

R3 still has its interface up/up:

R3#show ip int brief serial 1/0
Interface IP-Address OK? Method Status Protocol
Serial1/0 190.1.135.1 YES manual up up

If we want R3's interface to go down when R5 and R1 are no longer available we need to use multipoint subinterface. Let's create one on R3 and move the config over:

R3(config)#interface Serial1/0
R3(config-if)# no ip address 190.1.135.1 255.255.255.0
R3(config-if)# no frame-relay map ip 190.1.135.1 301
R3(config-if)# no frame-relay map ip 190.1.135.5 305
R3(config-if)#int s1/0.3 multipoint
R3(config-subif)# ip address 190.1.135.1 255.255.255.0
R3(config-subif)# frame-relay map ip 190.1.135.1 301 broadcast
R3(config-subif)# frame-relay map ip 190.1.135.5 305 broadcast
R3(config-subif)# no frame-relay inverse-arp

Bring up R5 and R1 again and now we have:

R3#show ip int brief s1/0.3
Interface IP-Address OK? Method Status Protocol
Serial1/0.3 190.1.135.1 YES manual up up

Shut down R5 and R3 is stil up but look at the debug frame-relay lmi. The status of PVC 305 is 0x0 which is inactive

R3#show ip int brief s1/0.3
Interface IP-Address OK? Method Status Protocol
Serial1/0.3 190.1.135.1 YES manual up up

*Mar 1 08:27:43.170: Serial1/0(in): Status, myseq 115, pak size 45
*Mar 1 08:27:43.170: RT IE 1, length 1, type 0
*Mar 1 08:27:43.170: KA IE 3, length 2, yourseq 115, myseq 115
*Mar 1 08:27:43.170: PVC IE 0x7 , length 0x6 , dlci 301, status 0x2 , bw 0
*Mar 1 08:27:43.170: PVC IE 0x7 , length 0x6 , dlci 302, status 0x0 , bw 0
*Mar 1 08:27:43.170: PVC IE 0x7 , length 0x6 , dlci 304, status 0x2 , bw 0
*Mar 1 08:27:43.170: PVC IE 0x7 , length 0x6 , dlci 305, status 0x0 , bw 0

Now let's shut down R1 and take a look at R3 again, notice pvc 301 is now status 0x0. and the interface is down/down on R3

*Mar 1 08:30:03.170: Serial1/0(in): Status, myseq 129, pak size 45
*Mar 1 08:30:03.170: RT IE 1, length 1, type 0
*Mar 1 08:30:03.170: KA IE 3, length 2, yourseq 129, myseq 129
*Mar 1 08:30:03.170: PVC IE 0x7 , length 0x6 , dlci 301, status 0x0 , bw 0
*Mar 1 08:30:03.170: PVC IE 0x7 , length 0x6 , dlci 302, status 0x0 , bw 0
*Mar 1 08:30:03.170: PVC IE 0x7 , length 0x6 , dlci 304, status 0x2 , bw 0
*Mar 1 08:30:03.174: PVC IE 0x7 , length 0x6 , dlci 305, status 0x0 , bw 0

R3#show ip int brief s1/0.3
Interface IP-Address OK? Method Status Protocol
Serial1/0.3 190.1.135.1 YES manual down down