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New Contributor

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11 Messages

Saturday, May 11th, 2024 11:41 PM

Router not honoring blocked devices, nor reserved IP addresses

Hi there, we just had a router failure and comcast replaced our Cisco router with a Technicolor CGA4332COM.  Having some weirdness now.

Our printer has needs a static (local) IP address.  So I reserved the proper IP with the printer's MAC address.  Seemed to work OK.  Then I got a call today- printer isn't printing.  Asked the person onsite to browse to the printer's management IP address- no luck.

Upon investigation, I found another device had been issued the IP address that is reserved for the printer.  How does that happen?

In order to remedy the issue, I blocked the device that was issued the "Reserved" IP address.  It still showed online, so I rebooted the router.  That enabled the printer to pick up its proper reserved IP address.  However, the printer does NOT show up in the list of connected devices- it shows up in the "offline devices" pane in the display.  

Then I noticed the device I had blocked was ONLINE after the reboot- it was issued a different IP address.  I double checked- the MAC address is in the blocked list, "Always" block.  And even in the "connected devices" list, the "X" on the far right- where you click to block a device- wasn't there!!  So the router knows it is blocked, but allows it on the network anyway.  Why??

The device with the reserved IP is hardwired ethernet  via an external switch if that makes a difference.  The "blocked" device is on WiFi via our Cisco mesh system which is also ethernet hardwired to the router (via an external switch)- it only does wifi, no DHCP or anything like that.  

So I have three problems in one issue here.

#1- Why does the router issue an IP address that I have set up as "reserved"?

#2- Why does that device with the reserved IP not show up in the connected devices list as being connected?  (Yes, it's connected, I can ping, print, browse the management interface, arp -a shows the mac address of the printer, etc.)

#3- Why is a device that has its MAC in the "Blocked Devices" list allowed on the network?

Thanks.  

Official Employee

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18 Messages

2 months ago

 

buckyswider - Thank you for reaching out! Customers may choose to manually set IP addresses for devices on their network. You must manually set the IP address and DNS server for each device that has a fixed (reserved) address. This must be done on the client computer, printer, etc. network settings. The CBR and BWG gateways can reserve IP addresses within the DHCP. This feature supports Advanced capabilities for these IP addresses including Port Forwarding, Port Triggering, Port Management, and DMZ. To add fixed IP address, in the Comcast Business Gateway Admin Tool, go to Connect Devices. If your device is already listed (on the network), select Edit. Then select the Reserved IP configuration and Save. If your device is not listed, select the ADD DEVICE WITH RESEREVED IP button.  Fill in the Host Name, MAC Address and Reserved IP Address, then Save. Configuring local area network (LAN) IP addressing.

 

New Contributor

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11 Messages

2 months ago

Hi Thomas, thanks for the reply, but did you read my question fully?  Or maybe you're a bot?    I have set a reserved IP address for a device, and the router's DHCP client gave that IP address to a DIFFERENT client.  

Official Employee

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18 Messages

 

buckyswider Apologies, I wanted to ensure I shared the steps so other readers may benefit. Let's take a closer look and troubleshoot together. Can you please send a direct chat message with your full name and complete service address to “Xfinity Support”? To do so, click on the chat icon located at the top right of this forum's page.
 
Here are the detailed steps to direct message us:
• Click "Sign In" if necessary
• Click the "Direct Message” icon (upper right corner of this page)
• Click the "New message" (pencil and paper) icon
• Type "Xfinity Support" in the to line and select "Xfinity Support" from the drop-down list
• Type your message in the text area near the bottom of the window
• Press Enter to send your message

 

New Contributor

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11 Messages

2 months ago

I may have some partial answers- but I'm not sure.

It is possible that the reserved IP address was issued before the address reservation was added to the configuration shortly  after the gateway was replaced.  But the gateway was rebooted many times after that- why didn't the gateway force the client to re-register after the reboot?  DHCP has a function FORCERENEW- which should be implemented any time the router notices an improper client which has a reserved IP that doesn't belong to it.  Possible yes, but after the gateway was replaced I browsed to the management interface of the printer to make sure it was working properly, and it worked then.  So I don't think that's the case, but it may be.

#2- Although DHCP gave the blocked client an IP address, I found a "reports" tab under "Content Filtering".  Running the report showed the MAC of the blocked client and a large number under "Attempts" - like 400, with "Device Blocked" listed.  I would think that blocking a device wouldn't even allow it on the network (i.e. deny the DHCP request) but it looks like it's just blocking all traffic.  Oh well.

Still no idea why the device with the reserved IP isn't showing up as a connected device.  And an arp -a says that the IP is dynamic.  Weird.  

(edited)

Official Employee

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18 Messages

Thank you for your feedback, buckyswider, as it may help other readers which is keeping in spirit with the nature of the Forums.