I’m on at least 2 blocklists at this point for the crime of not having reverse DNS set up. I don’t know how rDNS works. No amount of reading Wikipedia is helping me understand what I have to do.
I have a domain at a registrar which gives me bog standard DNS.
I have Apache running on my network.
I have PiHole running on my network.
My understanding is that rDNS is not set up at my registrar, but somewhere in my network. What do I do?
I have an ISP issued fiber modem that goes straight into my pfsense box. For IPv4 I have NAT and Firewall, for v6 it’s just the firewall. It should be noted that I’ve been hosting with this setup for years and it wasn’t a problem until I got this ISP at this location. I’ve had this ISP elsewhere without problems and another ISP here where it also wasn’t a problem.
The traceroutes getting dropped was a misconfiguration in my firewall on my part, it should work now!
My friend across town can now ping me successfully but going to my website still gives him ERR_CONNECTION_TIMED_OUT in browser.
EDIT ----------
I got another troublesome user to run a quick test with the new firewall config. Also can’t reach my website. Pings DO time out for him! Traceroute expectedly also fails, last hop was cpe.ae20-0.khk7nqp8.dk.costumer.tdc.net [87.61.121.169]
From my side, I now see 3 ???s between the CPE and your IP address, which is also responding, so that’s great.
Can your friend do something like curl -vvv https://drkt.eu or whatever to see if the time out happens before/after SSL handshake etc.? Also, do they have any firewalls / security appliances configured to filter content? I’d be curious to see dig or nslookup result, ping or traceroute result, and curl -vvv result, just to understand where it is breaking down.
Also, do you have a login to your ISP’s equipment? Are you able to set it to bridge mode to bypass it altogether? Just throwing ideas out there, to see if there is anything else on the go. That cpe device is also pretty curious for sure.
Office friend still can’t ping me. The campus friend can ping me but can’t reach my website. I never trusted campus friend to be on a clean network so it’s a bit fruitless to test his connection.
My ISP’s equipment is entirely a modem right now, bridging straight to my pfsense router. It’s not doing any weird filtering.
Here are the results of those from office friend
Server: unifi.localdomain
Address: 192.168.0.1
Non-authoritative answer:
Name: drkt.eu
Addresses: 2a05:f6c7:8039::1337
89.150.135.135
Tracing route to drkt.eu [89.150.135.135]
over a maximum of 30 hops:
1 <1 ms <1 ms <1 ms unifi.localdomain [192.168.0.1]
2 1 ms <1 ms <1 ms 5.186.33.65.static.fibianet.dk [5.186.33.65]
3 4 ms 4 ms 3 ms 89.150.66.104
4 4 ms 4 ms 4 ms ae2.core01-tkbg.bb.fibianet.dk [89.150.64.25]
5 * * * Request timed out.
6 3 ms 3 ms 3 ms 89.150.69.66
7 2 ms 4 ms 2 ms 217.74.211.104
8 3 ms 4 ms 4 ms 194.182.97.132
9 4 ms 4 ms 3 ms ae22-0.khk7nqp7.dk.ip.tdc.net [195.215.109.46]
10 4 ms 4 ms 4 ms ae1-0.khk7nqp8.dk.ip.tdc.net [83.88.12.15]
11 3 ms 4 ms 4 ms cpe.ae20-0.khk7nqp8.dk.customer.tdc.net [87.61.121.169]
12 * * * Request timed out.
13 * * * Request timed out.
14 * * * Request timed out.
15 * * * Request timed out.
16 * * * Request timed out.
17 * * * Request timed out.
18 * * * Request timed out.
19 * * * Request timed out.
20 * * * Request timed out.
21 * * * Request timed out.
22 * * * Request timed out.
23 * * * Request timed out.
24 * * * Request timed out.
25 * * * Request timed out.
26 * * * Request timed out.
27 * * * Request timed out.
28 * * * Request timed out.
29 * * * Request timed out.
30 * * * Request timed out.
Trace complete.
* Rebuilt URL to: https://drkt.eu/
* Trying 89.150.135.135...
* TCP_NODELAY set
* connect to 89.150.135.135 port 443 failed: Timed out
* Failed to connect to drkt.eu port 443: Timed out
* Closing connection 0
curl: (7) Failed to connect to drkt.eu port 443: Timed out
— UPDATE
Office friends pinged me 4 times, all timed out on his end. His IP showed up in my state table and I captured these 2 packets
State table:
Interface Protocol Source -> Destination State Packets Bytes
WAN icmp 5.186.33.87:1 -> 89.150.135.135:1 0:0 4 / 4 240 B / 240 B
Packet capture: (the only 2, despite the 4 pings, and they have bad checksums?) All 8 expected packets show up but all do have bad checksums. I’m seeing a LOT of bad checksums. A known working connection from fourth friend did not show bad checksums in this same test.
5.186.33.87 > 89.150.135.135: ICMP echo request, id 1, seq 43476, length 40
12:38:19.843890 d0:50:99:81:48:17 > 4c:6d:58:4a:97:d4, ethertype IPv4 (0x0800), length 74: (tos 0x0, ttl 64, id 21715, offset 0, flags [none], proto ICMP (1), length 60, bad cksum 0 (->1dc0)!)
89.150.135.135 > 5.186.33.87: ICMP echo reply, id 1, seq 43476, length 40
12:38:20.219177 d0:50:99:81:48:17 > 4c:6d:58:4a:97:d4, ethertype IPv4 (0x0800), length 43: (tos 0x0, ttl 64, id 32958, offset 0, flags [none], proto ICMP (1), length 29, bad cksum 0 (->3f6d)!)
He went to my domain while I was collecting packets from ANY protocol filtering his IP
It’s a bit long, so here’s the cap file https://u.drkt.eu/iiUsH7.cap
I’ve learned that the bad checksums are to to be ignored because it’s the NIC that’s responsible for it, so tcpdump sees the wrong checksums and it doesn’t matter. I have also learned that the Apache container actually does see the incoming connections. Here’s an example of my working connection and his connection.
Looks like connection are being made, so it isn’t routing after all!
Looking at the first recording, based on the different packet length, I’d guess it is doing SSL handshake properly; whereas the second one seems to be all 0 length and so something is not working out. At least on a cursory glance, your settings seems to be pretty permissive, so unless your friend’s using a super old system, it shouldn’t be an issue. Do you know what OS your friend is using, and if it has up-to-date root certificates? Are they on a system with openssl cli available? Judging by the unifi network, probably? Try openssl s_client -connect drkt.eu:443 -prexit (and ctrl + c to quit after it stops) and see if you can see any oddities with the SSL handshake process.
He’s running Windows 10, unfortunately- but wouldn’t SSL errors show up in Apache logs? His IP appears 0 times in all apache error and access logs dating back 8 months (the beginning of recorded logs).
Here’s another example of a working request to https://drkt.eu, and his non-working request respectively.
These are captured on both my gateway and the Apache LXC container. The captured packets are identical as far as tcpdump is aware on both of these systems. As far as I can tell, unless there are shenanigans at the firewall WAN NIC, this is how the packets arrive to my firewall.
And I don’t think this is asymmetrical routing if I understand it correctly, as I only have one firewall. My interfaces are configured correctly according to that netgate article.
Sorry I got slammed by work last couple of days and didn’t check back.
I wonder if it could be asymmetrical routing by your ISP? You mentioned your setup was okay before but it doesn’t work since you changed location.
I think your friend with the UniFi network has a static IP. Can you try traceroute to their IP and see if the route is similar to the one taken by their ISP? I’m not sure if this is how you’d test for asymmetrical routing but if nothing else the symptoms sound similar.
Typically, in a TCP connection, you’d SYN, SYN+ACK, ACK, then transfer actual data over. In the successful sequence, you see this happening as expected.
In the unsuccessful sequence, it seems to be stuck in SYN, SYN+ACK, but there is no ACK that follows (Flags [.]).
Where is the second one captured? On the user’s system, or on your system? Something in between is determining the packet isn’t intended for the destination and dropping it. It may be a firewall, it may be something else.
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I have an ISP issued fiber modem that goes straight into my pfsense box. For IPv4 I have NAT and Firewall, for v6 it’s just the firewall. It should be noted that I’ve been hosting with this setup for years and it wasn’t a problem until I got this ISP at this location. I’ve had this ISP elsewhere without problems and another ISP here where it also wasn’t a problem.
The traceroutes getting dropped was a misconfiguration in my firewall on my part, it should work now!
My friend across town can now ping me successfully but going to my website still gives him ERR_CONNECTION_TIMED_OUT in browser.
EDIT ----------
I got another troublesome user to run a quick test with the new firewall config. Also can’t reach my website. Pings DO time out for him! Traceroute expectedly also fails, last hop was cpe.ae20-0.khk7nqp8.dk.costumer.tdc.net [87.61.121.169]
From my side, I now see 3
???s between the CPE and your IP address, which is also responding, so that’s great.Can your friend do something like
curl -vvv https://drkt.euor whatever to see if the time out happens before/after SSL handshake etc.? Also, do they have any firewalls / security appliances configured to filter content? I’d be curious to seedigornslookupresult,pingortracerouteresult, andcurl -vvvresult, just to understand where it is breaking down.Also, do you have a login to your ISP’s equipment? Are you able to set it to bridge mode to bypass it altogether? Just throwing ideas out there, to see if there is anything else on the go. That
cpedevice is also pretty curious for sure.Office friend still can’t ping me. The campus friend can ping me but can’t reach my website. I never trusted campus friend to be on a clean network so it’s a bit fruitless to test his connection.
My ISP’s equipment is entirely a modem right now, bridging straight to my pfsense router. It’s not doing any weird filtering.
Here are the results of those from office friend
— UPDATE
Office friends pinged me 4 times, all timed out on his end. His IP showed up in my state table and I captured these 2 packets
State table:
Packet capture:
(the only 2, despite the 4 pings, and they have bad checksums?)All 8 expected packets show up but all do have bad checksums. I’m seeing a LOT of bad checksums. A known working connection from fourth friend did not show bad checksums in this same test.He went to my domain while I was collecting packets from ANY protocol filtering his IP It’s a bit long, so here’s the cap file https://u.drkt.eu/iiUsH7.cap
I’ve learned that the bad checksums are to to be ignored because it’s the NIC that’s responsible for it, so tcpdump sees the wrong checksums and it doesn’t matter. I have also learned that the Apache container actually does see the incoming connections. Here’s an example of my working connection and his connection.
We’re making progress!
Looks like connection are being made, so it isn’t routing after all!
Looking at the first recording, based on the different packet length, I’d guess it is doing SSL handshake properly; whereas the second one seems to be all 0 length and so something is not working out. At least on a cursory glance, your settings seems to be pretty permissive, so unless your friend’s using a super old system, it shouldn’t be an issue. Do you know what OS your friend is using, and if it has up-to-date root certificates? Are they on a system with
opensslcli available? Judging by the unifi network, probably? Tryopenssl s_client -connect drkt.eu:443 -prexit(andctrl + cto quit after it stops) and see if you can see any oddities with the SSL handshake process.He’s running Windows 10, unfortunately- but wouldn’t SSL errors show up in Apache logs? His IP appears 0 times in all apache error and access logs dating back 8 months (the beginning of recorded logs).
Here’s another example of a working request to https://drkt.eu, and his non-working request respectively.
Thinking about this some more, could it be asymmetric routing?
If so, does this help?
Replying to both of your comments:
These are captured on both my gateway and the Apache LXC container. The captured packets are identical as far as tcpdump is aware on both of these systems. As far as I can tell, unless there are shenanigans at the firewall WAN NIC, this is how the packets arrive to my firewall.
And I don’t think this is asymmetrical routing if I understand it correctly, as I only have one firewall. My interfaces are configured correctly according to that netgate article.
Sorry I got slammed by work last couple of days and didn’t check back.
I wonder if it could be asymmetrical routing by your ISP? You mentioned your setup was okay before but it doesn’t work since you changed location.
I think your friend with the UniFi network has a static IP. Can you try traceroute to their IP and see if the route is similar to the one taken by their ISP? I’m not sure if this is how you’d test for asymmetrical routing but if nothing else the symptoms sound similar.
See this page here that explains the
Flags: https://opensource.com/article/18/10/introduction-tcpdumpTypically, in a TCP connection, you’d SYN, SYN+ACK, ACK, then transfer actual data over. In the successful sequence, you see this happening as expected.
In the unsuccessful sequence, it seems to be stuck in SYN, SYN+ACK, but there is no ACK that follows (
Flags [.]).Where is the second one captured? On the user’s system, or on your system? Something in between is determining the packet isn’t intended for the destination and dropping it. It may be a firewall, it may be something else.