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R

Recognized Contributor

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30 Messages

Wed, Feb 24, 2021 9:11 PM

/59 prefix delegation block changed...

I have a /56 static on Comcast Business.  Recently I had a cable modem issue (as determiend by comcast) and the cable modem was replaced.  Everything is working, but I received a different /59  (still inside my /56) so I had to renumber several vlans!  How do I keep this from changing?  

Thank you,


Robert

Responses

New problem solver

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63 Messages

2 m ago

The most recent firmware update (about a week ago), pretty much broke IPv6. Whenever IPv6 routing dies: reboot the cable modem (about once a day) and it will come back. Don't hold your breath to get useful IPv6 support from Comcast, but if you find a fix, let us know ;-).

I had a lengthy discussion with various Comcast support people last year about these IPv6 issues, and the resolution from their IPv6 specialist was that with IPv6, Comcast does not offer static IPs, so you are out of luck. (never mind that the modem IS getting a static prefix, but the modem is messing it up).

Quick technical details:

Comcast assigns a /56 to the modem. One /64 is used for devices directly connected to the modem. Via DHCPv6-PD, a device may request a /59 (used to be /60, but that changed to a /59 last year).

IPv6 addresses are only routed by the modem if the prefix was requested by a device via DHCPv6-PD. You used to get an ICMPv6 Type 1 Code 5 if you used an IPv6 address before you received the DHCP assignment ("Source address failed ingress/egress policy"), but more recently, I have not seen these messages. Packets are dropped silently.

About a week ago, Comcast loaded a new firmware to my modem. (Software Image Name: DPC3941B_3.9p32s1_PROD_sey). With this update, a couple things changed:

* If your modem's prefix was 2001:db8::/56, you used to get 2001:db8:0000:00(c0)|(f0)/59 assigned to your devices. This now changed to 2001:db8:0000:00(00)|(20)|(40)/59. If you get the 2001:db8:0000:0000::/59: that once overlaps with the /64 assigned to the modem's network. 

* After about one day, the modem will respond with "No Prefix Available" messages. This message should be used to indicate that the prefix was assigned to a different device (but it isn't). Two workarounds: Use a different DUID (but now you will get a different prefix) or reboot the modem.


In short: disable IPv6 for a stable network, or pick a different ISP if you need IPv6 for your business.

Recognized Contributor

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30 Messages

2 m ago

@DCT-Michelle :

Hello & thank you for your response.

If every time a new /59 can be handed out, how am I supposed to statically ip my servers (web, dns, mail, etc) and have them work if the subnet can keep changing?  My /56 is STATIC.  How do I make my /59 static as well?  I pay for static ips!

@flybynight : I  have no other ISP option at this point.  I'm thinking I may just do an HE.NET tunnel.  Hopefully that will work better.

Official Employee

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12 Messages

Thank you @rob_hendelman_jr for the additional information and I understand your concerns. Can you please send us a private message by selecting the Comcast Business icon so we can get your account pulled up and take a closer look so we may better assist? 

New problem solver

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63 Messages

2 m ago

he.net works reasonably well (and you will get a static /48). The only issue with he.net is that some services (e.g. Netflix) are blocking them last time I checked. Netflix considers it a VPN as he.net could be used to bypass geo-restrictions.

The Comcast "upper tier" support I spoke with last time this issue came up told me that only IPv4 is "static" and they do not have a "static IPv6" product. I know... frustrating as it appears the modem is to blame here as the modem does receive the same prefix. This "you need to request a prefix to route" is stupid and appears to cause these problems. But then again, AT&T mobile does NAT for IPv6 "just because". Legacy carriers have no incentive to make IPv6 actually work right.

Recognized Contributor

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30 Messages

2 m ago

@Comcast_Alyssa , while I am able to tag you here, I am unable to direct message you.  Your name does not appear in the dropdown box, similar to my earlier problem with the other rep.  Are you able to send me a message that I can reply to?


Thank you,


Robert

Official Employee

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15 Messages

@rob_hendelman_jr No worries about finding a specific agent. Please make sure to just find Comcast Business in the options and then the messaging will follow. 

Recognized Contributor

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30 Messages

2 m ago

@Comcast_Jodie I don't see an "options" for messaging.  Where do I see that & make sure it's set to Comcast Business?


Edit: I reached out to a rep with "Comcast business" next to their name to ask for help.  I'll follow up here if I'm not contacted within the next few days.

(edited)

Official Employee

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15 Messages

@rob_hendelman_jr Ah, okay! Hopefully that works. If doesn't there should be a "message" icon in the upper corner. Then try to search the name Comcast Business to connect with us. 

Contributor

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21 Messages

2 m ago

My IPv6 setup broke around the same time frame.  Despite strong evidence to the contrary, Comcast has claimed the problem is beyond the demarcation line so they can't offer support.

Even if I got this working again there's no guarantee that it would keep working since it's obvious Comcast isn't adequately testing and maintaining their deployed equipment to support IPv6 prefix delegation use-cases for businesses.

So I've pretty much given up trying to get the modem to behave reasonably and I'm considering my alternatives.

New Contributor

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9 Messages

2 m ago

@Comcast Business I am requesting an escalation of the issues outlined in this post. We need engineering to take this issue seriously

Official Employee

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6 Messages

@MikeAce, I can definitely look into this further. I know you were initially having some issues with sending us a PM. Are you able to send us a message using the "chat bubble" icon at the top right-hand side of the site? It should be next to the notifications icon, and your forum icon at the top. 

Recognized Contributor

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30 Messages

2 m ago

@Comcast Business : Agree with MikeAce.  I'd like to know how/when/if this is going to be fixed.  I always viewed Comcast as a leader in the ipv6 space, and tbh, I'm starting to wonder....

New problem solver

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63 Messages

2 m ago

Hello @Comcast_Supportand thank you for responding out to us. I appreciate your response. It is not satisfactory, but thank you for sticking with us to make us feel like you are about out questions and concerns! I am willing to help! In order to get started can you please send me a private message so I can give you my contact information? I am willing to talk to an engineer who is able to fix the problem on the phone as part of my ongoing commitment to make the service I pay to do what I pay for. But I am not willing to spend time on hold, or waste time talking to sone with no ability to fix this problem.

New problem solver

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63 Messages

2 m ago

FWIW: I also noticed that since the firmware update, the modem's DHCPv6 responses set the T1 parameter to 5 seconds. This causes the router to renew the IPv6 prefix every 5 seconds. I guess this is a "hack" to make sure the modem is getting "primed" with the DHCP prefix quickly after it is restarted? 

Recognized Contributor

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30 Messages

2 m ago

I've reached out to @Comcast Business so hopefully I will hear something soon.  If I get it resolved I will post here what the resolution is.  I hope others will do the same.  I think even if we can get a standard way to handle dhcpv6-pd problems handled, that would be a positive step for others who have dhcpv6-pd issues in the future.

Recognized Contributor

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30 Messages

2 m ago

@flybynight : I think your best option is going to be to "private mssage" "Comcast Business".  It seems to me like it is a "role" account and someone may be assigned to you. 

New problem solver

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63 Messages

2 m ago

After having IPv6 drop again last night, I now finally broke down and gave Comcast customer support a try (via phone). Right now we are in the "oh. we do not support IPv6" phase of the call. Will post if something comes out of this.

New problem solver

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63 Messages

2 m ago

Got a call back from the customer service rep that again, Comcast isn't supporting IPv6, and I should ask "my IP guy" for help (her words, not mine). But she did agree to escalate the issue and I do have a ticket number now. 

Official Employee

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137 Messages

@flybynight

Hi there! I'm so sorry you are having issues. I'd be glad to ensure that this gets looked into further. Please click on my handle (ComcastRob) and send a private message with your name, the complete service address (including city, state, ZIP, suite number, etc), and the phone or account number, and any pertinent details-- like the ticket number(s)-- so we can help. 

 

New problem solver

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63 Messages

2 m ago

@Comcast_Robert just sent a message to "Comcast Business". Didn't see Comcast_Robert or ComcastRob as an option in the direct message dropdown.

Official Employee

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4 Messages

Uh-Oh, we apologize about that, but we did not receive your private message. Let's try this again and if it still doesn't work, we will have to further investigate the cause of this. Please try again by clicking the "message" icon in the upper right part of our forum page. Once you click on that, input our shared handle Comcast Business to send us a private message. 

 

We look forward to working with you on this!