Visitor
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2 Messages
Reverse DNS for my IP address is returning SERVFAIL
The reverse DNS for my IP address (in the 71.238.123.0/24 block) is returning SERVFAIL. This is not a request for a custom PTR record, I understand those aren't offered on residential accounts. The issue is that the existing reverse zone is answering inconsistently.
`dig -x <ipaddress> @8.8.8.8` returns status: SERVFAIL, while the same command against @1.1.1.1 returns status: NOERROR. Additionally, a network admin at a site I routinely connect to independently also sees status: SERVFAIL from their own resolver.
This has made fresh ssh connections for work take roughly 30 seconds longer than they should, a problem that only began when I got my new router, so I believe that I'm on a new IP whose reverse zone is broken.
I'm happy to provide the exact IP address privately.
Community Best Answer
dns_woes
Visitor
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2 Messages
4 hours ago
Xfinity was not able to resolve this issue for me, saying that they cannot fix broken PTR records for residential accounts. The best they could advise was to try to get a new IP address by leaving my router offline for a night.
I'm adding this information here in case it helps anybody else that runs into this issue. It seems that the problem is that the reverse DNS zone 123.238.71.in-addr.arpa has a broken delegation. It's delegated to two nameservers: dns1.inflow.pa.bo.comcast.net and dns1.cmc.co.denver.comcast.net. The former didn't respond to queries from my network on IPv4 or IPv6, the latter just returns a referral that lists itself and the former server as the zone's nameservers. With one server unresponsive and the other lame, no resolver can get an authoritative answer, so reverse lookups for any address in 71.238.123.0/24 fail (8.8.8.8 returns SERVFAIL, while 1.1.1.1 returns NOERROR but with no answer).
Fortunately, I had a different router already, so I just switched my xfinity hardware into bridge mode and switched to my other router, which (luckily) got me a new IP address that doesn't have this issue.
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XfinityJeniece
Official Employee
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4.3K Messages
7 days ago
Hey there, @dns_woes, thanks for reaching out through Xfinity Forums regarding your DNS issues. We would be happy to take a look at this issue on our end and help with troubleshooting. Please send us a Direct Message with your full name and your full address.
How to Send Us a Direct Message:
You can see how to send us a direct message here, https://forums.xfinity.com/conversations/guidelines/how-to-direct-messaging-within-the-forum/697ba1e570934d009185c514.
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