CCIE Pursuit Blog

August 22, 2007

Frame Relay Inverse-ARP Weirdness

Filed under: Cisco,Cisco Certification,IOS,Lab Tips,Tech Tips — cciepursuit @ 9:05 am

I came across an interesting Frame Relay inverse-ARP issue:

Here’s my intitial configuration (Frame Relay inverse-ARP disabled):
r4(config-if)#do sh run int s0/0
Building configuration…

Current configuration : 136 bytes
!
interface Serial0/0
 description ->r1 FR (spoke)
 no ip address
 encapsulation frame-relay
 shutdown
 no frame-relay inverse-arp
end

Let’s turn on Frame Relay inverse-ARP:
r4(config-if)#frame inv
r4(config-if)#do sh run int s0/0
Building configuration…

Current configuration : 143 bytes
!
interface Serial0/0
 description ->r1 FR (spoke)
 no ip address
 encapsulation frame-relay
 shutdown
 no frame-relay inverse-arp IP 405
end

WTF???  Where did that command come from?  Here’s the IOS version that I’m running:

r4(config-if)#do sh ver | i IOS
Cisco IOS Software, C2600 Software (C2600-ADVENTERPRISEK9-M), Version 12.4(10),
RELEASE SOFTWARE (fc1)

This command was something that I had configured on an earlier lab.  Even though I had turned off Frame Relay inverse-ARP (“no frame inverse”) for the ALL DLCIs, once I re-enabled it, it restored the old configuration that was disabling Frame Relay inverse-arp for DLCI 405 only.  This is a good “feature” to be aware of so it does not bite you in the ass on the exam.  [I should have just defaulted the interface instead of peeling off commands one at a time 🙂 ]

Let’s make sure that Frame Relay inverse-ARP is enabled for all DLCIs:
r4(config-if)#frame-relay inverse-arp IP 405
r4(config-if)#do sh run int s0/0
Building configuration…

Current configuration : 108 bytes
!
interface Serial0/0
 description ->r1 FR (spoke)
 no ip address
 encapsulation frame-relay
 shutdown
end

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