DHCP problems

I am a network engineer who runs a company that builds country wide Internet distribution systems.

My home network is a /22 network centered on a MikroTik 4100 router connected to an ARRIS S33 Modem. I use 8 wifi hot spots in a MESH network, all operating in Bridge mode. The controllers of this MESH are connected to the MikroTik by Enet (Gb). The WIFI hotspots provide no services other than access. Everything is controlled by the router. The MikroTik has a DHCP client on the ether 1 interface which should get a real IP address from the Comcast DHCP server. It does from time to time. Oddly, the lease on the address tends to be 1 hour. At the end of that 1 hour lease, the DHCP client process no longer gets an address from the Comcast servers and the network goes offline thinking it has no valid configuration.

If I go into the router and hand code in the Address that was previously assigned by the DHCP server, and add a default route pointed at the gateway your server provided, I can bring the network back up. To the router, this looks like I have a STATIC address. This will last until the DHCP client of the router acquires a new address from Comcast Sometimes this is months later, sometimes 2 weeks, sometimes 4 hours.

A little while ago we had a short outage in our area. When your network came back up, the MikroTik acquired an address from the Comcast server with a 4 day lease time. At the end of this 4 days, the network went offline. When I went to check it, the MikroTik acquired a new address, this time with the same 1 hour lease time. After the lease expired, no new lease was given and I reprogrammed the router as I explained above.

Any ideas what could be going on?

Responses

CCEthan

Official Employee

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1.4K Messages

3 years ago

Hi, @macrhino1. You have quite the setup going and sounds awesome! In this situation, we first like to do all the basic checks of signal and area to make sure there is not more than one issue and go from there. Can you send a private message with your name and address?

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5. Press Enter to send it. An official employee, such as myself or whoever is first available, will respond. Thanks!

(edited)

macrhino1

New Poster

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11 Messages

3 years ago

Thank you Ethan. I have done this on Twitter. This went back and forwards until they washed their hands of it. I have posted their last message to me. It does not make any sense to me. Here is the last response from Xfinity with my comments in brackets.

"I'm sorry - to clarify, our DHCP server is set to send an IP to a modem, itself. Your MicroTik router from earlier is a subnetting issue and beyond the demarcation of a residential ISP. [I don't understand how a DHCP address is a subnetting issue]

The technician noted that the resolution of the troublecall was for home networking, and our networking engineers would be unable to assist. As a residential ISP we're not able to help with this. [I did not ask for help in home networking, I wanted someone to work with who had access to the DCHP server.]

I would reach out to support from MicroTik, as our DHCP servers are only assigning external IP addresses to the modem on the account, and your router deals with any subnetting lease times within the scope of residential services. DHCP lease request is client side. [The Arris S33 is a level 2 device. The address from Comcast is assigned to my router, not to the modem. "Subneting lease times??" ]

If the registered modem on the account is getting the IP, then that's as far as Comcast is able to go on the residential services. I do see that a myriad of agents have tried to assist in the scope that we're able to help with, and even then, our engineering team is not able to assist with subnetting. [The registered modem is not "Getting the IP" and I do not know what they mean about subnetting. I can't see how this has anything to do with subnetting.]

I'm sorry that we've reached an impasse here, but if there's anything further my team and I can answer, I'm happy to do so! Once again, we really think a business account would better fit your needs, as those accounts are equipped to handle further dives into the demarcation that you're seeking. Let me know if you have any further questions. -Meagan [This also does not make any sense at all]

Here is a previous response:

Ok, I have an update! I touched base with my support team, explained the situation, and had them read everything over. The general conclusion was that the residential system is working as intended, and that the current ask is outside of what residential services can provide--and you'd be more suited with having a business service installed as a home-based business account, as that can provide the features you need for this particular instance. There are technical and network restrictions when it comes to residential internet services: https://comca.st/37fDD2F [I have no idea what the "Current ask" is. I want a reliable DCHP allocation with sensible lease times. I do not know what features I am supposedly requesting. This seems like an upsell ]

You may still receive contact from the networking team that the tech supervisor wrote up, though they may advise of the same situation described above. If you'd like to contact business services, and inquire about an in-home set-up, their number is (800) 391-3000.

IN this exchange I was told :

1. I am asking too much ( I am not asking for anything Comcast does not do for any other residential customer)

2. This is a modem problem. (Modem worked fine, and in spite of that I replaced the modem. Nothing changed)

3. They said they can’t help configure my router (yet no one has asked for help in configuration, nor would I let them.)

4. They said this is a subnetting issue. (not possible)

5. Concast sent a hardware tech to the house, both he and his supervisor knows the issue is not with me. (They have told me as much)

6. They said I was running a business out of my house. (Not true)

7. They send me a link implying I am not using the service correctly. (Acceptable use policy. Nothing in that link applies to this problem. )

8. They say “we can’t help you configure your home equipment (Yet I have never asked for this and quite frankly I doubt that many of the people responding to me could configure a Mikrotik 4011.)

Perhaps you will understand why I am loathe to go through this again. I would simply like to have someone on Xfinity's side who actually understood networking. I am fully prepared to say this is my problem but someone needs to tell me in ways that do not defy basic networking.

(edited)

XfinityJoeTru

Official Employee

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7K Messages

Thanks for replying with the details. We apologize for any less than satisfactory experience. We strive to improve all customer experiences, and we never want customers to feel the way you do. Unfortunately, we (tech support) have no control over the DHCP server when it comes to lease timing for a dynamic IP address. Business services were mentioned because there, you can purchase static IP's and not have the IP leases and dynamic changes. For most home internet users, our dynamic IP lease times never impact the average every day internet user. We would love to help you, but our troubleshooting demarcation does not reach engineer level, or network specialist level, and since your internet is not experiencing trouble with connectivity, performance, or reliability under normal home uses, we have limitations in how we can help. We appreciate your understanding, and thank you for choosing Comcast as your service provider.

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3 years ago

macrhino1

New Poster

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11 Messages

The problem is not lease times per se. If the lease times were one hour and they were renewed, there would be no problem. The problem is that the lease expires and the DHCP server does not renew the lease. I don't care what the lease times are. I just want the DCHP server to work the way DHCP servers are supposed to work. I want nothing more than is supplied to every other residential customer.

What is really frustrating is that I am paying for service that I am not getting and the only way to fix my problem is to pay 3X of what I am paying now for business class service. This is akin to buying a Toyota, having engine trouble and being told, No one here can fix this so you need to buy a Lexus since Lexuses do not have that problem. Why is it that someone who does have access to the DHCP server can not help?

Imagine being a customer and getting this as a response:
"If it happens that quickly then it was automatically assigned a short-term DHCP but after that it should just be renewing dynamically as usual. What is your suggestion that you think will fix it from our end? -JEG"

!!!!!??? What is my suggestion for fixing it from your end? This is a question asked of someone who does not know your internal network config or how you are providing DHCP to end users.
The AMAZING part for me is that you have someone on my end with both the Knowledge and equipment to provide DCHP logs in DEBUG mode and TCP dumps. No one has asked for these logs.

I understand your limitations as techs. I run a company that owns an ISP in New Mexico and we support 300+ systems from our offices using your business class service. Why can't I be put in touch with someone who has the ability to discuss this and troubleshoot the problem?

3 years ago

XfinityJoeTru

Official Employee

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7K Messages

Again, we sincerely apologize for the experience you've been having trying to get the support you need. I can offer to submit a ticket for you to our Advanced Repair Team, and there one of our Tier 2 support techs will contact you to further discuss your issue and any options we have. To get started on that, Please send us a message with your full name and service address to Xfinity Support. To send us a message, you'll need to sign into the Forums if you are not. Then you'll need to locate and click on the "Direct Message" Icon located in the upper right corner of this page. Next, click the "New Message" (paper & pencil) icon and type "Xfinity Support" in the to line and select "Xfinity Support" from the drop-down list. You can proceed to type your message in the text area near the bottom, and press enter to send the message.

3 years ago

Jlavaseur

Problem Solver

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948 Messages

3 years ago

So, it’s either a dhcp assigned ip or manual assigned ip, my understanding you can’t do both simultaneously, so if you assign a manual ip, which you seem to have done, the dhcp server won’t assign a ip, plus manual ips and dhcp server ips, fall in different ip ranges, unless it’s a reserved ip, just my thoughts

EG

Expert

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107K Messages

@jlavaseur

I believe that they are referring to the WAN / public IP address that is assigned by the Comcast DHCP server.

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3 years ago

Jlavaseur

Problem Solver

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948 Messages

@EG maybe i don't understand correctly, he said this: The MikroTik has a DHCP client on the ether 1 interface which should get a real IP address from the Comcast DHCP server. Then he claims: If I go into the router and hand code in the Address that was previously assigned by the DHCP server, and add a default route pointed at the gateway your server provided, I can bring the network back up. To the router, this looks like I have a STATIC address. This will last until the DHCP client of the router acquires a new address from Comcast Sometimes this is months later, sometimes 2 weeks, sometimes 4 hours. , but once the Comcast IP changes, the *hand coded* is no longer valid, thus breaking his connection, am i missing something?

3 years ago

macrhino1

New Poster

•

11 Messages

Ok let's try this one more time. The way this should work is that the Mikrotik uses a DHCP client to acquire a public address from Comcast DHCP server. This happens from time to time, usually with a 1 hour lease time. This lease, being a WAN connection, causes the Microtik to insert a default route into the routing table using the gateway provided by the DHCP server.

When the 1 hour runs out, the DHCP client ATTEMPTS to get another lease, since the old one has expired. It should get a new lease, most likely with the same IP address as the last one, but this is not guaranteed. In any case, IF the DHCP client was to get the new lease, the router would change the table, if needed, and the connection would be fine.

BUT THIS DOES NOT HAPPEN. The DHCP client, more often than not, fails to get the new lease. The network, having no route out, goes OFFline. AT THAT TIME, if I go in, while the network is offline, and manually insert the old lease and manually insert the old entry to the routing table, the network goes back online. This "PSUEDOSTATIC" addressing would not be necessary if the system were working as it should.

It is not serious that I should wait weeks for the DHCP server to respond, being offline the whole time. If the system was working the way it should, I would NEVER have to reprogram the router.

Is this clear now?

3 years ago

diamondlake

Visitor

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1 Message

@macrhino1 Hi there -- I am having the exact same issue myself. I have a Motorola modem which more often than not fails to renew the WAN side IP address via DHCP and then the network goes offline until I perform a hard reboot of the modem. I am wondering if you made any progress on your problem? I am also wondering if you have any devices plugged into the switch ports on the actual modem? I have tried support and had a technician out to verify the signal, etc. but I am getting no where.

3 years ago

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DHCP problems

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