Hi Brian,

I ran into these nasty frame relay mappings during an initial lab set-up and was wondering why they are there, (even with inverse-arp disabled), and what they are actually doing. I was able to remove them only after writing my configuration to memory, and then performing a reload of the router.

Router(config-if)#do show frame map
Serial0/0 (up): ip dlci 113(0x71,0x1C10)
              CISCO, status defined, inactive
Serial0/0 (up): ip dlci 105(0x69,0x1890)
              CISCO, status defined, active
Serial0/0 (up): ip dlci 104(0x68,0x1880)
              CISCO, status defined, active
Serial0/0 (up): ip dlci 103(0x67,0x1870)
              CISCO, status defined, active



Hi Josh,

This is actually an error relating to AutoInstall over Frame Relay. When the router boots up and does not have a configuration file saved in NVRAM, it attempts to run autoinstall to automatically find an IP address and download a config. The first thing the router does is to detect the encapsulation on its WAN interfaces, which in this case is Frame Relay. Once the router finds that it’s running Frame Relay, it attempts to send a config request via TFTP. In order to do this it needs an IP address, so it sends a BOOTP request out all DLCIs. Since the router doesn’t know what the unicast IP addresses are on the other ends of the circuits, it creates IPv4 mappings to for all circuits and includes the “broadcast” keyword on them. This allows the router to encapsulate the BOOTP request out all DLCIs.

If you haven’t actually configured IP helper-address or a BOOTP server, the operation will fail. The result of this that we see is that when Frame Relay is re-enabled on the interfaces the mappings to reappear. In some versions of IOS this can be fixed by removing Frame Relay and re-applying it, for example:

router#config t
router(config)#interface s0/0
router(config-if)#encapsulation ppp
router(config-if)#encapsulation frame-relay

In most versions however this does not work. Therefore the way to fix this is just to have the router not do autoinstall on bootup. Since the router does autoinstall because it doesn’t have a config saved in memory, the only way to 100% fix it is to save your config to NVRAM (wr m), and to reload.

About Brian McGahan, CCIE #8593, CCDE #2013::13:

Brian McGahan was one of the youngest engineers in the world to obtain the CCIE, having achieved his first CCIE in Routing & Switching at the age of 20 in 2002. Brian has been teaching and developing CCIE training courses for over 10 years, and has assisted thousands of engineers in obtaining their CCIE certification. When not teaching or developing new products Brian consults with large ISPs and enterprise customers in the midwest region of the United States.

Find all posts by Brian McGahan, CCIE #8593, CCDE #2013::13 | Visit Website

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9 Responses to “Understanding Frame Relay Mappings to”

  1. ovais says:

    Dear Brian and all, i figured another way to remove these mappings, these mappings also usually appear when in some way our frame-relay config is not correct, like when we make multipoint interfaces and have more then one dlci so router confuses which dlci to be applied on which multipoint interface and thus creates this mapping ( this is what i observed in my practice lab, anyhow if its wrong kindly tell us ), so to remove it without reloading the router u need to do this

    int se 1/0
    no encaps
    encaps frame-relay
    no keepalive
    no shut

    now since router will not run keepalives it will not run any dlci and so mappings arent there ;-)

  2. ovais says:

    One thing more, may be someone might also say that there might be a drawback of turning off keepalives since we will not be able to learn our dlci(s), what i think is that as an administrator we need to know what dlci are assigned to us, so we will know the dlci(s) anyway, and regarding the status of other device we could employ end to end keepalives also, what you guys think ?

  3. Some versions you can remove them by stopping and starting Frame Relay (no encap, encap). As for LMI keepalive if the exam question asks you to disable it, disable it. If they don’t say anything about it, don’t touch it ;)

  4. ovais says:

    Ok Brian, thanks for the feedback :-)

  5. Adult Ühler says:

    Thank you for this. Helped sort my problem out. I did CCNA back in school, but my teacher had not passed the final and he gave us all the answers for all the exams. So I don’t know as much as I should do :) .

  6. Wonderful site, I truly discovered it to be informative. I am looking forward to visiting once again to ascertain what is brand new.

  7. [...] Check for mappings in frame-relay. I lost points on PIM related tasks for leaving them on the router (great explanations here). [...]

  8. Sabeer says:

    Hi Brian.. that was a nice explanation. Thank You!!!!!!!!!!!


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