Comcast XFINITY → Linksys/Comcast DHCP Solution?

I've been working on this problem for the better part of three nights, trying to figure out what's going on and to come up with a solution short of replacing my Linksys BEFSR router or switching to DSL. I think I may have the solution, at least for now.

This problem first cropped up for me, and several other Maryland people on March 28. That day, my connection went dead for hours and I noticed the Linky was reporting an IP address of 0.0.0.0. Repeated attempts to manually renew gave no relief. I also noticed that my Motorola 4100 log showed it losing synch, and upon reboot might take 20 attempts to get a DHCP response from Comcast. I called T/S and got a recording telling me that there were problems in my area and that "some" customers would have no connectivity for a while.

I went to work. When I got home that night, the connection was indeed restored. But I found that about once an hour it would go down. Every time the symptoms were the same. IP in the Link showed that 0.0.0.0 and it might take ten or twenty manual renews before it would snatch a valid IP. Then I'd be up again, and an hour later, back to no connection. This continued steadily until today. If the modem were connected directly to the PC, the PC would get an IP address and be on-line.

Now to the nitty-gritty. What I have discovered, and what may have been completely obvious to everyone else, is that the firmware version I was using on the Linky, 1.40.2, was renewing the DHCP lease once each hour, like clockwork. I'm sure it has been doing this all along, but I never noticed because it would instantly get a response, and I would have no problem. When the Comcast DHCP server began to hiccup, this caused a serious problem because the Linky only tries to renew the lease one time. If it doesn't get a response that time, you have the 0.0.0.0 IP and no connectivity.

So there was a combination of factors contributing to the problem. First, for reasons unknown, the Linksys router on V. 1.40.2 of the firmware insists on renewing the DHCP lease every hour, even though that lease is good for 7 days. Second, the Comcast DHCP server was being flaky and often required a few attempts before responding. Third, the Linky wouldn't ask for the lease more than once so that didn't play well with the second problem. This is why connecting directly to the PC solved the problem. Windows is much more persistent about getting the DHCP info than the Linky is.

I experimented with the latest version of the firmware, 1.42.6. As has been well documented here, that version is much worse, actually attempting to renew the lease every two minutes! Combine that with a flaky DHCP server and you are in deep weeds.

So I've now dropped back to version 1.39 of the firmware. 8 hours later, it hasn't tried a lease renewal yet, and I've been surfing to my heart's content. Tomorrow I'll know if it is going to try to renew after 24 hours, or if will just let the lease go to expiration. In any event, for me the problem is over.

Now the problem would have dissipated anyway, as luck would have it, as of today the Comcast DHCP server is back to responding on the first attempt. But I feel a lot better with a router that doesn't try to renew a 7-day lease every hour or every two minutes, and I know that if the DHCP server breaks again, it won't be causing me problems every hour or every two minutes.

Anyone who is interested can get the downgraded 1.39 software here: ftp.linksys.com/pub/befsr41/befsr-1-39.zip

With all due respect, this problems has been hashed out in numerous posts in the Hardware area.

John

Hmmm, well with all due respect right back, I've been reading those threads for three days without finding a solution as it relates to the Comcast DHCP issues. They deal with the frequent renewal of the 1.40+ firmware versions without respect to what it is doing to certain specific Maryland Comcast users who have been suffering through this since the 28th. And the basic solution being offered is to drop back to 1.40.2, which most of us with the problem have been using from the start. I can also find no discussion of what a Linksys router does when it doesn't get a DHCP response, as opposed to what Windows does, which isn't of much importance to anyone who doesn't have an ISP whose DHCP server isn't working correctly. I also find no discussion of a one hour renewal being a problem, again, because if the DHCP server is working correctly, it isn't.

So my point in bringing this here, instead of there, is that there are specific issues with these firmware versions as they relate to a current issue with Comcast in Maryland. Glad you aren't suffering through it in Troy.

PetD,

Good info, glad to see someone else working on this. I was doing the same thing last night. When I backed off to 1.40.2, I thought everything was fixed but I was watching the lease timer last night and sure enough it keeps renewing, Fortunately, the DHCP server here responds quickly and it's just a minor hiccup. I'll have to read more in the Link board, I thought it was just 1.46.4 causing the problems. I never see anything in either the Link log or the 4100 log showing that it did this.

I'm lucky, at this location I get sync and DHCP almost immediately ( not to rub salt in the wound).

Ron

I have never upgraded my firmware from
1.39,if it isn't broke why upgrade at
all?

Even in the Linksys documentation it
says something like "only upgrade the
firmware if you are having problems".

I too had DHCP problems a week or so
ago but it was nothing on my end,it
was one of Comcast's servers causing
the problems.

Skip

PetDude,

I thought I'd chime it and let you and others know that I've so far been OK as well. But for me, things worked out even without switching to an older version of the firmware. If you remember, I mentioned that under WINS (Windows 98),
I chose (not sure why it wasn't already checked -- may be the first time I called Comcast tech support they told me to uncheck it, go figure!), "USE DHCP FOR WINS RESOLUTION".
Remember I said that that seemed to have made things better... Guess what, last night, things were really good and the connection was stable as prior to March 28th.

So my guess here is that it might have been combination of ny configuration setting (the WINS one) and Comcast DHCP server behaving sporadically... Just a guess.

WINS resolves NetBios names to an IP address. It's only needed if the Network your on is using NetBios and serves no purpose other than matching a Computer or Server name on the network to an IP address.

My point is that it was probably just a coincidence that your performance was better. Checked or Unchecked it shouldn't matter.

Yeah, stant_98, I have to agree with LarryJ5. The WINS resolution setting just has nothing to do with it. At the time you and I were have the discussion about it, the Comcast DHCP server was coming around. By night before last it was much better, by yesterday it was responding to requests immediately. As I said in my post, the problem would have gone away if I (or you)had done nothing, as the DHCP server became responsive again. My concern is not having a repeat performance. If the DHCP server becomes flaky again, and you are still on one of the 1.4+ versions of the firmware, then you are going to have problems. WINS resolution won't help you. It is completely unrelated.

well i am knocking on wood so far i have not had these issues..i also have not upgraded the firmware..and now i suppose i never will..its 1.39 forever lol thanx for the heads up Petdude

I am in S.E. Michigan and I had some DHCP probs with my linky and the new firmware. I noticed that everytime I did get an IP it was the same one. So I configured it for static instead of dynamic. A month later no problems... I don't know if you guys have tried this, or if it is an exception in my area, but it worked for me...

Yep, Gremlin, I did try that, and it also solves the problem, but there is a catch. If your IP does change, you are going to get knocked offline and/or whoever gets assigned your old IP may be in the same boat. The second problem is you are setting yourself up to get your IP changed as well, by not renewing the lease when it expires. A DHCP server won't issue your IP to another user while the lease is valid unless you release it. If you renew it immediately upon release or lease expiration, you are very likely to get the same IP again as the DHCP server will give you back the one you had if it is still available. In your case, by setting up static, once the lease expires the server might just hand your IP to another user, depending upon how it is configured. It is possible to set up the DHCP server so it won't issue an IP that is already being used on the network, but we have no assurance that is the case here. In fact, early on in the transition several users reported here that after setting up as static for a time, they lost connectivity. Also there were posts from people who go knocked off-line when the IP the Comcast DHCP server assigned them was already in use by another user who had it statically set.

Another method would be to set up with a static IP, then release and renew the lease through a power cycle occasionally. I like not having to do anything. The question I still have, and won't know the answer to for a time, is whether the 1.39 firmware will wait to renew until lease expiration. In my mind, that would be perfect.

Of course, all of this is a moot point if the DHCP server that services your node is malfunctioning as was the case in my area on 4/1. I couldn't get an IP address anyway or anyhow for 5 days until someone figured out there was a problem with DHCP! It took numerous phone calls to tech nonsupport and a visit by field techs to verify the problem. Having the router connected or disconnected didn't make a difference. I finally got back online last Saturday and I have had two different IP addresses since then. Would you say that's a problem with DHCP or with Linksys firmware?

I would say its both. If you are using the a version of the firmware greater than 1.39, then you are attempting to renew your IP at least once an hour, and perhaps once every two minutes. Imagine this scenario. You have an IP assigned by the Comcast DHCP good for 7 days. An hour later your router releases the IP. It tries to renew but the malfunctioning DHCP server does not respond on the first try. So rather than continue trying, your router gives you an IP of 0.0.0.0. An hour later, it tries again, and this time has success. Except that your old IP has already been issued to someone else, so you get a new one.

Thanks for such full explanation! I will see how the performance goes, and if Comcast DHCP servers get weird on me/us, I will then install an older version of the firmware.
For some reason, I'd like to make sure of that myself; LINKSYS keeps persisting that the latest firmware is used unless, specifically, unless, it's proven faulty. That's exactly what I'd like to find out for myself if I get that chance. Let's hope though I won't and Comcast resolves the DHCP server issue (I got a feeling they will not as quickly as we all wish).

Thanks again!

Hmmm. I'm on firmware 1.40.2. I agree with you that it makes very little sense to attempt to renew the IP address every two minutes. That's an unnecessary use of bandwidth and it is a huge point of failure in a flaky DHCP environment such as this one. Ultimately, the problem is with Comcast's DHCP server if you disconnect the router and attach directly to the CM's ethernet port. If you can't release/renew and get an IP address then the problem is entirely theirs as long as you have networking setup properly on the client. I know you already know that, I'm just trying to explain the troubleshooting steps I went through. I was able to briefly get an IP address that I assigned statically and that got me limping along at very slow speeds until DHCP was functional on Saturday.

Question: How do you tell that the router is trying to renew it's IP address every two minutes? That seems very lame to me.

mdcompguy, you are renewing once an hour with that version, not once every two minutes. You can tell by going to the Linky's status page and watching the time you have left on your lease. Yours will never show a time of less than 6 days, 23 hours. If you watch, when it hits 6 days, 23:00:00, it will then immediately go back to 7 days, because it renews at that point.

I hear you on the issue of this being a Comcast problem. I don't in any way deny that, it certainly is. But it is the combination of the Comcast DHCP issue with the Linksys constant renewal that is making it unbearable. Like you, there was a short time when I could get no DHCP information at all. The modem would continue to recycle because after 10 attempts it still had no DHCP response. This was the time that the Comcast recording was saying my area was experiencing problems. At some point, however, the modem started to get a DHCP response again and stopped recycling. A check of the logs showed that it was still not getting a DHCP response until it tried multiple times, however. At this point, I could plug the modem into the PC directly and get on line, because as I mentioned earlier, the PC will not give up if it doesn't get a DHCP response on the first attempt.

One thing to keep in mind is that unless you have cloned the MAC address of your PC's LAN adapter into the Linky, you cannot simply unplug the modem from the router and into your PC and have connectivity. When your modem boots, it registers the MAC of whatever it is connected to at that point. If it is connected to another MAC it won't connect. To make it connect, you would simply need to reboot the modem after connecting to the PC and again when it’s back on the router. If you did all that, then I guess your Comcast DHCP server was hard down for longer than mine was!

I lived in Southern Maryland. I have made no changes and magically I was able to keep an IP address for more then 2 minutes. It started to become reliable the morning of April 8, 2002.

I immediately noticed that indeed the DHCP lease will jump back to a full 7 days after about 1 minute and 50 seconds. At the moment it is working. I am afraid to even turn my PC off in fears that all will go to hell again.

I never paid much attention to the DHCP least before March 28 so I really do not have any benchmark. I am going to Linksys and push them on this DHCP 2 minute problem. Thanks to all.

x062pea, you are describing the exact same phenomenon. As of yesterday, the Comcast DHCP server started responding on the first attempt, so everything starts working, even with a two minute or one hour renewal. Looks like you are on 1.40.6. Give 1.39 a try, and relax. Still holler at Linksys, but at least you won't be going through the two-minute drill next time Comcast's DHCP server burps.

use win for dhcp is what comcast tells you to set settings on as i install it. with @home it would usually work whether or not it was checked but it is def. supposed to be checked with comcast

And it definitely doesn't make a bit of difference. By checking this off you are telling your computer to get the WINS server IP from the DHCP server. There is no WINS server IP so you get nothing back. This is quite easily verifiable by doing an ipconfig /all. See? No WINS server. If there was one, you would see a line that said "Primary WINS server.....xxx.xxx.xxx.xxx.

Please try to understand this. WINS resolution provides NetBios names over differing network segments. This is done through NetBios calls. Since Comcast, like any ISP with the slightest concern about security blocks NetBios calls, having a WINS server would be fairly idiotic.

Let's say there was a WINS server. You check off "Use DHCP for WINS resolution". The DHCP server obliges and sends you the address of the non-existent WINS server in fairyland. This registers your computer name and IP with the WINS server in fairyland. Now you happen to be on the same node with me, and I do the same thing. Cool! Now when I go to Network Neighborhood or My Network Places I can see your computer and all your shared devices, you can see mine and we can use each other's stuff! Sound like a bit of a security issue to you?

In reality, since there is no WINS server, and since there is no fairyland (sorry) checking this off does NOTHING. Your computer simply requests a WINS address and doesn't get one. No harm done, no benefit either.

Rody, this is an example of why coming to a forum like this and regurgitating a tier one script isn't usually terribly helpful. Your script says do it that way because that is the Windows default when the IP is set to automatic. They obviously don't want you to mess with what you don't understand, so they show you default settings. Simple as that.

Petdude,

Are you like a walking manual, or something?

Good Job, Man!

PetDude,
PROBLEM IS BACK! Started again tonight, 7:30 pm; at least that was when I ran into it once again.
I'm not sure whether you will get it too; but it's back where I live (Silver Spring, MD)

First, I'm going to try to install that older firmware for the router. Then, hopefully, as you said it won't be ocuring this often

Comcast truly sucks.... I'm soooo sick and tired f it!

Damn!

I hear you stant, I hear you. I won't be home till late, so it will be a while before I know how much my Comcast High Speed Internet service is under-performing this evening.

[text was edited by author 2002-04-10 20:04:18]

I had the same problem. I actually downgraded to 1.40.2 and it started working "better." (didnt need to go ALL the way back to 1.39). I think the servers also improved around here. Its probably a combination of things failing.

Wow. I had not realized that my DHCP renews every hour. Thanks for pointing that out. I was having the 2 minutes renewal blues when I went down to 1.40.2, but I never bothered to check and make sure my DHCP was really going the distance. Well I'm going to try going back to where I started with the 1.39's and see where that gets me.

astrokat, It works better because you only have the opportunity for trouble once an hour now. If you go to 1.39, likely you will have that opportunity only once a week.

Sanguinelust, it was a shock to me as well. So far 3 days on 1.39 so it looks like to me it will go the whole week. Not a darn thing in any of the higher versions I seem to need.

I don't see anything in the higher firm's that appeals to me either. I just figured I would give the newer ones a try to see if they might makes things better with my speed and or connectivity issues. Obviously they do not.
[text was edited by author 2002-04-10 21:33:12]

Apparently, this version isn't renewing after an hour. Here's the info on my Linky Status screen (minus a little bit). I edited out the stuff with x's. I did as you suggested by putting my LAN adapter MAC address in the Linky MAC address clone so I don't need to restart the CM if I change my connection. Other than that, no more problems...for now. Thanks for your suggestion and the info.

Host Name:
Firmware Version: 1.40.2, Oct 23 2001

Login:
Disable

LAN:
(MAC Address: xx-xx-xx-xx-xx-xx)
IP Address: 10.10.10.1
Subnet Mask: 255.255.255.0
DHCP server: Enabled

WAN:
(MAC Address: xx-xx-xx-xx-xx-xx)
IP Address: 68.48.xxx.xxx
Subnet Mask: 255.255.255.0
Default Gateway: 68.48.xxx.xxx
DNS: 68.48.0.5
68.48.0.6
68.48.0.6
DHCP Remaining Time: 6 days 17:44:24

Do not feel bad. Mine problem is back in Southern Maryland. Linksys sent me 1.42.4 but it made no difference. I am trying to convince Linksys to take a more serious look at it. A sniffer did not reveal anything from Comcast that should be causing the Linksys 2-minute DHCP problem (other then poor response). All I see is ARPs, DNS fowarding, and some minor traffic. Nothing that correlates to 2 minutes. I am getting frustated as well. Let me know if that older firmware works. An hour is not all that long either.

Well I had the 2 minute resets with ver. 1.42.6. When I dropped to 1.40.2 I thought my problems were gone because I had not bothered to check after the 2 minute problem disappeared. When Petdude pointed out the 1 hour reset, I checked it out and sure enough I was resetting every hour too. I finally went back to my original, no problem, 1.39 and now everything seems to be working again smoothly. I'm currently closing in on 24 hours, actually I'm only minutes away from 24. I'm sure things will be ok again now as I had no problems with 1.39 before. I suggest you go get 1.39, unless you like renewing every hour.