Thursday, December 12, 2024
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Alice AUSTIN

Alice AUSTIN is studying Cisco Systems Engineering. He has passion with both hardware and software and writes articles and reviews for many IT websites.

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26 thoughts on “ISP DHCP Server Issue And ARP”

  • After getting past the initial DHCP issue and getting stuck with that lack of ARP response, I did a connection kick via their online portal and it came back. No need for a new router after all 🙂
    I wonder why their ARP responses got stuck in the first place.

  • Change ISP and go with Future Broad Band. You will not disappoint. Static IP and all the enterprise functions you want!

  • We have had similar issues a couple of times with Aussie Broadband, though I don't believe it to be a strictly ISC-DHCP issue, but instead more general.

    We are a corporate customer with AussieBB and we resell their NBN services to a number of our customers.

    We have noticed that sometimes the AussieBB DHCP servers just do bizarre things. (That is not counting the full outages caused by outright failure of AussieBB's DHCP servers as mentioned by KaldekBoch)

    One customer in particular that I remember went offline last November after 2 years of faultless service.

    They are on a business NBN FTTB service, so should have a proper static IP address and not just a sticky IP address.

    For customer firewalls, we deploy a pretty vanilla Debian Linux boxes running Shorewall, additionally if the NBN service is FTTN/FTTB we deploy a basic VDSL modem in bridge mode.

    Side note you should try Shorewall out in one of your videos one day, it rocks for easy to use, but also very very powerful Linux firewalling. (Especially when managed with Ansible)

    Anyway this customers connection just dropped for no apparent reason out of the blue one day.

    I went on site expecting a faulty hardware swap and ended up spending hours there to resolve it.

    The customer was not getting an IP address on their service anymore.

    TSharking traffic I could see DHCP discovers going out, but not getting a DHCP offer responses.

    Lucky as a corporate customer we have direct access to (usually) helpful phone support.

    They confirmed they could see my DHCP discover coming in, but they also confirmed that their DHCP server was NOT sending a DHCP offer response. (Which was what I was seeing with TShark at my end)

    The person I was dealing with could not explain the lack of response.

    We tried all sorts of things over the next nearly 2 hours on the phone.

    Swapped VDSL modem to different model & brand, tried connecting my Windows laptop instead of the Linux firewall to take that out of the equation, tried setting both VDSL modems I had with me to routed mode instead of bridge mode to see if they would get a DHCP response.

    No hardware or OS swapping at my end could resolve things, it was always the same result, DHCP discover going out, but no DHCP offer coming back.

    In the end what resolved the issue was an IP address change on the service.

    The AussieBB tech changed the IP address on the service and everything came up within seconds.

    The VDSL modem could get an IP address in routed mode, my Windows laptop could get an IP address when I bridged the VDSL modem, and finally our Linux firewall got an IP address again.

    When the tech tried changeing the service IP address back to the original address all of a sudden the DHCP offers stopped coming back and we went back to the original symptoms.

    To just resolve the issue I got the AussieBB tech to change the IP address of the service once again, it was only mildly annoying to change a few records at our end for the benefit of getting the customer back online as it was not worth the effort to keep the old IP address.

    The tech was going to raise it with the network engineers for a post-mortem as the problem should never have happened, but I never heard anything back and we never persued it as the customer was back online and it wasn't worth our effort.

    When I discussed it with other guys in our office after the fact it turned out that someone else has had an identical issue with a different service with AussieBB (NBN FTTN).

    And the only resolution there was the same, change the service IP address.

    Definitely something weird with AussieBB's DHCP servers and I have never been entirely happy with them myself.

    DHCP server issues is one of the reasons why at home I use Future Broadband, they basically just resell TPG IP-Line, so no DHCP servers to worry about as their services are statically routed.

    I just set my static IP address and gateway on the WAN interface of my firewall and the service just works. (I also got an additional /29 from them too which is handy to play with sometimes)

  • I've just churned to Launtel today after yesterday's DHCP server outage. Two DHCP server issues in a year with ABB where their entire DHCP service went offline for more than half of Australia! DHCP is not a service to let rot.

  • You should have a backup router to verify. Something as simple as a home wifi router.

  • Table exhaustion for mac's and stuff is a big problem. I wonder if this is their problem, that's a mighty big network /22 for "one" interface. That's 1000 addresses there, a few more networks and a bunch of idiots with weird bridge interfaces with multiple Mac addresses just smells rife to be a problem.

    They could also have some kind of *pon limitations for how many concurrent devices you can "plug in at once".

    Sounds like a pickle, good luck getting in touch with the right people to get it sorted.

  • Have you tried change Mac-adress on external interface. I have seen isps blockning Mac-addresses from Raspberry pi and other known servers.

  • Paul, long time veteran of cable ISPs (25 years). At least for them, in most cases the cable modem is configured to trust any CPE device behind it. And when the offer comes to their IP relay device (a CMTS), the device usually takes advantage of option 82 (circuit ID) and adds the info about what cable modem is attached. The DHCP service then trusts any CPE behind it and responds with the offer. The cable modem also has a security feature to where only one MAC addresses is stored on the CPE side so that users cannot connect 20 devices and get 20 public IP addresses. Not until the cable modem is reset will it refresh that MAC table that it learns from the CPE. Operators can of course choose to increase the amount of CPEs learned if they desire. This may explain the ARP issue that until you "kicked" the connection. not sure what that means, but maybe you rebooted the service provider's modem, ONT, or whatever the ISP gives you for equipment. I know PON operators also leverage DHCP option 82 frequently too to trust unknown CPE, when connected to a "trusted" device they deploy.

  • Would be really interested in how you have your 4G backup setup + SMS!

  • I had the same issue. Use a repurposed riverbed running pfsense and ABB wouldn't pass any traffic. Use their supplied modem (got it free so why not) and …. it works. Couldn't get the cnts to resolve it, so I just bridged the modem they gave me and stuck it inline on the WAN. It works fine, but I don't like it.

  • This is interesting, the dhclient issue must be new because my router is using dhclient and I'm with Aussie. My dhclient is 4.3.3. I would suggest using the website/app and bringing down you link completely and then kicking your link. Aussie use Cisco BRAS systems which has caused them issues in the past (ipv6 dhcp memory leak being one) Maybe the Cisco does not like the extended dhcp packet header.

  • AussieBB Hack here. I called having issues at the beginning. I asked them to remove CGNAT due to port forwarding requirements. It broke my Mikrotik hard and faced similar but not the same issues. I ended up turning the port blocking on and off a couple of times on their troubleshooting app which made it work. I think it may be something with their initial firewalling that drops the packets after their routers. give it a try and and see.

    All in all could you imagine asking this query to telstra…. you'd be 98 years old still trying to explain what a raspberry pi is.

  • What is the 4g modem you are using for your backup. I am looking for one and really not sure which I should get. Also what is the antenna. Like you I have crap mobile reception.

  • Just reading the comments and I saw ABB mentioned – I suddenly had visions of Asea Brown Boveri pushing packets at kiloAmps down cables as thick as a guy's leg at 22kVolts !

  • My mate at ABB said they do DHCP reservations pegged to the MAC address of your wan interface that sticks upon reboot of the router and you can kick your own connection from the Aussie broadband app

  • Any thoughts about moving that 4G external Antenna to the roof? Also please do another video on your SMS setup.

  • very interesting. who knows what tomfoolery they are doing behind the seens to "fix" the issue

  • I just got this latest response… another "change the router" line of bullshit

    "Thanks for all the information you have sent through. I have spoken to my Level 2 about this issue and at this point, we would like to test another router connected to see if the same issue is occurring on another device. If you are still having the same IPv4 issue, we might need to escalate this to our Network team for further investigation."

    Kill me 🙁

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