Visitor
•
5 Messages
Very short *WAN* DHCP leases and Internet disconnection on every lease renewal
I've spoken with Comcast first-level phone support, second-level phone support, Advanced Technical Support, and Customer Security Assurance about the problem in the subject, all to no avail. I'm hoping someone here can connect me with the group that can address the issue.
Similar problems have been reported in these forums before. Some of the reports can be found via https://www.google.com/search?as_q=wan+dhcp+lease+only+2+hours&as_sitesearch=forums.xfinity.com
For more than a year, Comcast has been supplying WAN DHCP leases of two hours or less to my equipment. While the short WAN DHCP leases would not be a problem by themselves, it is a problem that every time my equipment renews the WAN DHCP lease, the Comcast equipment drops my Internet connection for many seconds.
Because the short WAN DHCP leases require frequent renewals, my Internet gets disconnected more than 24 times a day. Disconnections occur regularly during my business hours and "freeze" my SSH connections to remote hosts.
Here is a summary of the facts known and diagnosis done to date:
- The WAN disconnect problem is not due to signal issues:
The first thing Comcast first-level support did was send a technician to my house, who replaced a number of connectors and splitters at the premises. As expected due to the nature of the problem, while the connector/splitter work did improve the signal quality (which was acceptable, if not outstanding, to begin with), it made *no* difference to the WAN disconnect issue. - The WAN disconnect problem is not caused by my router:
I have removed the router from the network and reproduced the WAN disconnect problem with a computer connected directly to the cable modem. - The WAN disconnect problem is not caused by my cable modem:
Comcast second-level technical support requested that I test with an Xfinity modem, which I am currently using in place of my cable modem. The short WAN DHCP leases and the WAN disconnect problem are identical using the Xfinity hardware or my cable modem. - The WAN disconnect problem is not related to customer-premise equipment generally:
The problem mysteriously "cured" itself for a time during December 2022, then reappeared in January 2023. My hardware, firmware, and configuration remained the same during that entire time. Obviously, hardware does not spontaneously "heal" and "re-injure" itself in this fashion, so the problem is not local to my premises.
Thank you
user_079458
Visitor
•
21 Messages
2 years ago
The short DHCP leases shouldn't be a problem by themselves. I checked my connection and I can see that the lease times are between 1 and 2 hours. This isn't a problem as the IP doesn't change so when my router does DHCP request and gets a reply - it doesn't do anything but extend the lease time.
In your case it sounds like the DHCP replies coincide with interruption on Xfinity's side. The best way to confirm that is to connect the computer directly to the cable modem, run continuous ping and then run tcpdump with a filter that captures ICMP request/replies from the ping with the DHCP request replies. If you see ICMP requests going on but the ICMP replies stopping when the DHCP request/reply happens - that would indicate a problem on Xfinity's side.
4
0
flatlander3
Problem Solver
•
1.5K Messages
2 years ago
Do you have the ability to disable IPV6 on your equipment for a test?
A long term issue in my market is communication with IPV6 servers. Works for a few days, communication to their IPV6 server is not available for a while (sometimes hours), and it screws up routing. I've tried various ways to overcome this, including requesting DHCP6 over IPV4, but nothing is stable here.
IPV4 only does actually work. At least for what I need to talk to. I'd rather go with a stable connection than a random flake out. When that no longer works for me, another ISP will be my answer. Might be your temporary solution too.
1
0
Jlavaseur
Problem Solver
•
948 Messages
2 years ago
Well I just remembered a trick from back in the day, so right now I have my router set to static ip instead of automatic, static might not be the correct identification, but the box is labeled that, works great, protocol prevents you from trying to inject a random ip address in to the dhcp server, but since I already know the ip, submask and default gateway, you can kind of trick it, it only lasts until Comcast changes your ip, then it breaks, but how long is that, mine is over a year, since the methods you tried involved most likely a dhcp server and client, it might possibly make a difference…
2
0
Jlavaseur
Problem Solver
•
948 Messages
2 years ago
My point is that ip combination is already assigned, you have to use it exactly, any deviation and it will fail, so when Comcast sends out dhcp info on my routers end there is no dhcp client to accept it, like i said it kind of tricks it...
1
0
Jlavaseur
Problem Solver
•
948 Messages
2 years ago
You can’t really go static, because a real static ip falls outside of the dhcp ip server range, it’s just a trick, I just thought a different approach might reveal something or not, I did specify that when the Comcast ip changed it would break….
0
0
user_079458
Visitor
•
21 Messages
2 years ago
I did this on my connection:
tcpdump -i cxl0 -n -vv -e -K ether host [Edited: "Personal Information"] and \(host 9.9.9.9 or port 67 or port 68\)
the cxl0 is my WAN interface and [Edited: "Personal Information"] is the MAC of the WAN interface. Xfinity doesn't filter traffic for neighbors so without it you would see traffic for other people connected to the same segment. After tcpdump was running, I started a ping to 9.9.9.9 and waited for IP to be renewed. These are the lines when it happened:
...
[Edited: "Personal Information"] [Edited: "Personal Information"] > [Edited: "Personal Information"], ethertype IPv4 (0x0800), length 98: (tos 0x0, ttl 63, id 50088, offset 0, flags [DF], proto ICMP (1), length 84)
X.X.X.X > 9.9.9.9: ICMP echo request, id 33674, seq 262, length 64
[Edited: "Personal Information"] [Edited: "Personal Information"] > [Edited: "Personal Information"], ethertype IPv4 (0x0800), length 98: (tos 0x20, ttl 56, id 51793, offset 0, flags [none], proto ICMP (1), length 84)
9.9.9.9 > X.X.X.X: ICMP echo reply, id 33674, seq 262, length 64
[Edited: "Personal Information"] [Edited: "Personal Information"] > [Edited: "Personal Information"], ethertype IPv4 (0x0800), length 342: (tos 0x10, ttl 128, id 34060, offset 0, flags [none], proto UDP (17), length 328)
X.X.X.X.68 > [Edited: "Personal Information"]: BOOTP/DHCP, Request from [Edited: "Personal Information"], length 300, xid 0xa2674ae4, Flags [none] (0x0000)
Client-IP X.X.X.X
Client-Ethernet-Address [Edited: "Personal Information"]
Vendor-rfc1048 Extensions
Magic Cookie 0x63825363
DHCP-Message Option 53, length 1: Request
Client-ID Option 61, length 7: ether [Edited: "Personal Information"]
Hostname Option 12, length 2: "fw"
Parameter-Request Option 55, length 10:
Subnet-Mask, BR, Time-Zone, Classless-Static-Route
Default-Gateway, Domain-Name, Domain-Name-Server, Hostname
Option 119, MTU
[Edited: "Personal Information"] [Edited: "Personal Information"] > [Edited: "Personal Information"], ethertype IPv4 (0x0800), length 358: (tos 0x48, ttl 56, id 35672, offset 0, flags [DF], proto UDP (17), length 344)
[Edited: "Personal Information"] > X.X.X.X.68: BOOTP/DHCP, Reply, length 316, xid 0xa2674ae4, Flags [none] (0x0000)
Client-IP X.X.X.X
Your-IP X.X.X.X
Client-Ethernet-Address [Edited: "Personal Information"]
Vendor-rfc1048 Extensions
Magic Cookie 0x63825363
DHCP-Message Option 53, length 1: ACK
Server-ID Option 54, length 4: [Edited: "Personal Information"]
Lease-Time Option 51, length 4: 7200
Subnet-Mask Option 1, length 4: 255.255.252.0
BR Option 28, length 4: 255.255.255.255
Default-Gateway Option 3, length 4: X.X.Y.Y
Domain-Name Option 15, length 20: "hsd1.ca.comcast.net."
Domain-Name-Server Option 6, length 8: 75.75.75.75,75.75.76.76
RN Option 58, length 4: 4039
Hostname Option 12, length 2: "fw"
[Edited: "Personal Information"] [Edited: "Personal Information"] > [Edited: "Personal Information"], ethertype IPv4 (0x0800), length 98: (tos 0x0, ttl 63, id 50303, offset 0, flags [DF], proto ICMP (1), length 84)
X.X.X.X > 9.9.9.9: ICMP echo request, id 33674, seq 263, length 64
[Edited: "Personal Information"] [Edited: "Personal Information"] > [Edited: "Personal Information"], ethertype IPv4 (0x0800), length 98: (tos 0x20, ttl 56, id 52128, offset 0, flags [none], proto ICMP (1), length 84)
9.9.9.9 > X.X.X.X: ICMP echo reply, id 33674, seq 263, length 64
...
As you can see, 600ms after the last ping reply, my computer sends a DHCP request to renew its IP. Xfinity replies right away with the same IP. 400ms later another ping request goes out and the reply comes immediately. At no point the lines goes down and the lease is extended.
Perhaps if you try the same and show how Xfinity stops replying to the ping requests after the DHCP reply - that would be a good clue that the problem is on Xfinity's side.
(edited)
1
0
EG
Expert
•
109.1K Messages
2 years ago
@user_079458
Please redact MAC addresses and the IP addresses from your post for your privacy. They are considered to be personal information. The posting of personally identifiable information is a violation of their forum guidelines. The forum bot will not allow your post to be seen publically. It flagged your post as "Private".
(edited)
1
0
EG
Expert
•
109.1K Messages
2 years ago
@user_079458
Please also redact the MAC addys and the IP addys from your post that begins with this sentence;
"I wouldn't say a problem solvers as these suggestions are not about solving the problem but more like determining that it is Xfinity that is at fault or not.
I did this on my connection:"
It's still marked "Private".
(edited)
0
0
user_079458
Visitor
•
21 Messages
2 years ago
@flatlander3 The dhcp6 is a different issue. In my case Xfinity stopped responding to dhcp6 solicit requests 20 days ago. Now ipv6 only works if using Xfinity's modem and only if set with bridge mode disabled. It is as if they placed a firewall rule that they will only respond to dhcp6 solicits from they own modem. I tried with my own modem - no response anymore. The Xfinity modem has an ipv6 address on the WAN in all cases. When their modem is configured with bridge mode disabled, I can see how their modem gets a /64 network and starts serving ipv6 ips on the lan interface. Prefix delegation doesn't work anymore. Previously I would get prefix /60 with the dhcp6 reply. Now I started getting "No prefix available"
0
0