13.2 DHCP - excluding router IPs

Shouldn't the solution also have us exclude existing static assigned IPs, i.e. R1, R4, and R6's IPs?  I've always practised excluding any IP that would be statically assigned.  In this case, we're given a range, but we also have the existing router IPs that I think should be excluded.

Comments

  • Totally agree with you. After reading the config guide for dhcp, it seems like there is another way to ignore BOOTP packets:

    ip dhcp bootp-ignore

    Does anyone know the differences between "ip dhcp bootp-ignore" and "no ip bootp server"?

    Eric

  • Totally agree with you. After reading the config guide for dhcp, it seems like there is another way to ignore BOOTP packets:

    ip dhcp bootp-ignore

    Does anyone know the differences between "ip dhcp bootp-ignore" and "no ip bootp server"?

    Eric

     

    May be it is a bit late for reply but "ip dhcp bootp-ignore" is used when you have both bootp & DHCP server in the network so a reuest made by dhcp server can be answered by DHCP server as well, so that you can configure it to selectively ignore bootp requests.

     

    Cheers

    Inder Vaid

  • This might help from the config guide:

     



    Address Conflicts


    An address conflict occurs when two hosts use the same IP address.
    During address assignment, DHCP checks for conflicts using ping and
    gratuitous Address Resolution Protocol (ARP). If a conflict is detected,
    the address is removed from the pool. The address will not be assigned
    until the administrator resolves the conflict.

    http://www.cisco.com/en/US/docs/ios/ipaddr/configuration/guide/iad_dhcp_svr_cfg_ps6441_TSD_Products_Configuration_Guide_Chapter.html

     

    So bascially those addresses will not be used in the pool as long as they respond to ARP or can be pinged.

     

    Regards,

     

  • Based on the wording of the task 'configure router as dhcp server for hosts on vlan x, but to ignore BOOTP packets' - well that says to me to configure the DHCP server right there to ignore BOOTP. It does not say to me disable the bootp service in global configuration.

     

    I suppose it could be possible that both are correct though.

     

    I also have a bit of a problem with the lease time specified since lease times are defined but the way the DHCP protocol is written a 24 hour lease time configuration really means 12 hours. It may be a case where I 'know too much' and then end up getting it wrong though.

  • Hi,

      If you speak about "ip dhcp bootp ignore" vs "no ip bootp server", these achieve the same thing. As for the lease, do you make reference to the fact that the client will try and renegotiate its IP address on half of the lease time? Even if the server does not respond it still keeps it for the lease time.

    Good luck with your studies!

  • Can anyone explain the logic of excluding the VLAN 58 default router's IP address in task 13.4, not excluding the default routers (R6 & R4) in task 13.2?

  • Hi,

      By default, the Cisco DHCP routers pings each address before allocating it to a client, regardless if the client is directly connected or through a relay; generally speaking it is stillr ecommended to exclude known IP address from the DHCP range, so this should be the case for both 13.2 and 13.4, it makes no sense to exclude it just in one case.

    Good luck with your studies!

  • Hi Cristian.

    That brings up an interesting question.  In the real lab, would you exclude the default router IPs and any other routers on the local segment, or would you not?

    Thanks for your response.

    Erick

  • Hi,

      I would, again, ask the proctor if task is not clear to exclude some addresses or not, but i think it should be: i would say, hey Mr Proctor, i know the IOS will ping any IP address before it rents it to a client, but should i exclude these IP addresses just to be on the safe side?

    Good luck with your studies!

  • Thanks a bunch Cristian.  I appreciate the response.

    Erick

  • If you speak about "ip dhcp bootp ignore" vs "no ip bootp server", these achieve the same thing.

    Slightly disagree because "no ip bootp server" disables the bootp service but still allow dhcp service to run and bootp request can also be served by dhcp server therefore for this task to ignore the bootp request on the dhcp server "ip dhcp bootp ignore" is necessary.

  • hey Mr Proctor, i know the IOS will ping
    any IP address before it rents it to a client, but should i exclude
    these IP addresses just to be on the safe side?

    I can almost hear the proctor saying- "Do what you think is best." to
    this question. I
    think in this particular case there would be no harm in excluding the
    addresses as you suggested however as pointed out by some of the other
    posts is not entirely necessary due to the built-in addressing conflict
    feature you've also mentioned.

    I think either way would be correct. If in doubt as opposed to get
    the "Do what you
    think is best" reply, you can choose to apply both solutions and as long as
    it doesn't break any task requirement/restrictions.

    A typical case
    would be for example OSPF authentication for a given area- should I do
    it under the interface or under the process? If the task doesn't really
    specify and you can't decide you could even apply both solutions and it
    wouldn't be incorrect. You will
    certainly be wasting some precious time as I doubt any task would
    require you do both as opposed to just make sure authentication is
    enable, but I guess this would be the peace of mind price to pay for the
    most paranoid and insecure ones out there- myself included at times.

    So
    to exclude or not to exclude? In this particular case, I think the task
    requirements are pretty clearly and I personally wouldn't. However, if doing
    so would give you extra peace of mind to move on with the other
    task/lab, exclude them...

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