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New Member


3 Messages

Sun, Dec 16, 2018 11:00 PM

IPv6 networking functional outbound, but inbound traffic is lost

We have a prefix deligation, it is 2603:3026:138::/56


Our Barracuda F80 router has four ports.  port 4 is connected to the Comcast Gateway (cable modem).


The F80's configuration assigns a static IP address to port 4 of 2603:3026:138::1.  The F80 also has the default gateway  (::/0) address the same as the Ipv6 address of the Cable Modem's interface ( 2603:3026:138::80b2:34ff:fe4a:37b3)


To clarify:

            2603:3026:138::80b2:34ff:fe4a:37b3                                 2603:3026:138::1

Internet-------> Cable Modem--->CM Interface--->CM Switch<----F80 Port4<----F80 Router



The Barracuda F80 is able to ping such addresses as 2001:4860:4860::8888 and it gets a reply.


However, if I go to a web site such as and try to ping my F80's port 4 IP address, I don't get a reply


If I ping the Cable Modem's IP address (the really long one above), I get a reply


If I login to the Cable Modem and use the troubleshooting tools and ping the IP address of port 4 of the router, that works just fine as well.


Apparently, the cable modem is having trouble routing packets destined for the 2603:3026:138::/56 network to port 4 of my router (2603:3026:138::1).


I suspect it needs to know that 2603:3026:138::1 is the gateway for the 2603:3026:138::/56 network and for some reason it isn't realizing this.    It is almost as if the Comcast Modem isn't doing IPV6 autoconfiguration correctly or something....or perhaps my router is at fault.




I just got off the phone with tech support and the nice lady had me put our Cable modem into Psedo Bridge mode.   However, there is no routing information on how to route packets onto Comcast's network in this configuration, and I am therefore unable to make it work.


It also broke IPv4 routing as well.  So I am not sure Psedo Bridge mode is the answer.


How do I resolve this?


Thank you









Official Employee


56 Messages

4 y ago

Sorry to learn you are having a problem with routing traffic. I would like to review the configuration of your Comcast Business Gateway to see what is going on. Please send me a private message with your Comcast Business account number, along with your name and complete service address. 

New Member


1 Message

2 y ago

What was the resolution to this? I have a Barracuda F80 Firewall with Comcast Business Internet as well and have never been able to get the /56 prefix working. My issues are the exact ones described previously.

Problem solver


348 Messages

2 y ago

Hi there, thank you so much for taking the time to reach out to the Digital Care Team here through the forums. You have reached the right team to help get this taken care of. Can you please send us a private message with your name, the full address, and phone/account number?