Yet another ping problem with Virtual IPs

[rebi]

Blimey! Case got quite weird ... but seems like nothing related to pfSense :)

Of course, I had tried this first from two machines but they were my laptop and another desktop machine at home (HPs if that matters) ... so, after I spent quite some time looking at packets without any clues, while trying to capture yet another one, I run the ping from a server console (data center) that was handily open and it worked ok. That's how I got suspicious ... then ping from the router itself (my home) was ok, ping from a windows server (office network) was ok, ping from a colleague's laptop (his home) was NOT ok. Today I asked the same colleague to do the same test from his laptop in the office network ... it was ok :) So, after talking with him I figured out we used different models same vendor routers at home (mine is using vendor's firmware, his is openwrt-based if that matters) as well as places where I tested and it worked, routers were pfSense and Mikrotik (and probably Cisco in the data center).

So, I'll assume it's something to deal with that vendor routers and won't bother researching it any more ... unless someone thinks it's too weird to be passed over :)

Edit: I've just tested with an OpenVPN connection to the office (using redirect-gateway def1) and it's working ok, so it seems problem is somewhere in these routers NAT implementation or whatever it is (it's not firewall as I've already tested disabling it).

[stephenw10]

So those initial ping requests that fail never arrive at the pfSense WAN?

Steve

[rebi]

bummer ... they all arrive on WAN but I can only see the successful ones on LAN.
I'm not sure I understand what's going on ... :/

[stephenw10]

Ok so to be clear you ping a VIP from somewhere external and, for example, you see 4 failed pings then a successful one at the client end.
In packet captures on pfSense you see all 5 ping requests arrive on the WAN but only one leaves the LAN?

And nothing is blocked in the firewall?

It's hard to imagine what could cause that. All of those pings on all the VIPs are forwarded to the same internal IP/MAC right?

Steve

[rebi]

Yes, whenever I alternate the pings first time I have between 1 and 4 failed pings and these pings are captured as requests on WAN but not LAN ...
And to confirm what my theory is ... I can't reproduce it today as I'm in the office

I promise to give it a second thorough look when I get back home. Indeed, it's hard to imagine what would cause that ...

[stephenw10]

You would see that if for some reason the first 4 ping requests were blocked by the firewall, you should see that in the log though.
Otherwise I'd try to see if they are being misrouted somehow. Though since everything is going to one internal IP it can't be something like a missing ARP record.

Steve

[rebi]

d'oh, I guess I'm not skilful enough to find exactly what's going on ... but will summarize whatever I've experienced so far:

Environment summary:
I have a virtualized environment in a data center - single server with a single network cable which carries a bunch of IPs. A pfSense VM serves as firewall, router, ids (monitoring-only) and OpenVPN server. All other VMs are behind this VM in local networks (virtual vmbr devices). Except one of the IPs which is set as WAN, the rest are set up as Virtual IPs of type "IP alias". Since one of the VMs is a reverse proxy to various web services in the internal network, its local IP is set up as 1:1 NAT to the virtual IPs in use. An ICMP rule on the WAN allows ICMP echo requests.

The problem:
Let's assume IP1 and IP2 are virtual IPs with set up 1:1 NAT to the reverse proxy VM local IP.
The following behaviour is experienced:

• ping IP1 - works
• ping IP2 - not working between 1 and 4 pings then starts replying
• ping IP2 - works
• ping IP1 - not working between 1 and 4 pings then starts replying
• latter happens every time I alternate the IPs when pinging

Findings:
The above behaviour is confirmed to happen from 3 different places where the only thing in common is the usage of TPLink router (official firmwares - one is OpenWRT-based, rest are using TPLink firmware). Strangely enough, it doesn't happen when pinging from router's diagnostic page. I see everything working as expected in lots of different networks, incl. behind a mobile TPLink 4GLTE MiFi router.

Current packet captures observations:

• ping IP1 - works
  Here I can see requests from my IP and replies from IP1 in the packets
• ping IP2 - not working between 1 and 4 pings then starts replying
  WAN packet capture - For all pings that do not go through I see "No response seen to ICMP request" in for the request packet (in latest Wireshark)
  Firewall logs - nothing
  LAN packet capture - I only see the successful ICMP requests and responses and I do not see these marked with "No response seen to ICMP request"
• ping IP2 - works
  Again, I can see requests from my IP and replies from IP2 in the packets

[stephenw10]

Try adding portforwards for ICMP to the same VM. They will override the 1:1 NAT.

If the pings arrive on WAN but never leave LAN something must be preventing that. Possibly it's unable to create a state on LAN as one exists from the previous ping.

Steve

[rebi]

Port forwards didn't help.

Here's what I've found with states:
I filtered states by ICMP and whenever I ping from my office network, I got states immediately created whenever I execute the pings. However, when alternating the pings from my home network I don't see the second state immediately, it gets created after a while.

So I did the following test:
I opened 2 command prompts and executed simultaneous continuous pings. I did this from both networks. While it worked ok from my office network, I can only see one of the pings working from my home network - the other one gives "Request timed out" until I cancel the other one and then in a few seconds it starts working. The second pair of states was never created for the second ping from my home network while both pairs were always created for the pings from my office network.

[Derelict]

@rebi said in Yet another ping problem with Virtual IPs:

Yes, whenever I alternate the pings first time I have between 1 and 4 failed pings and these pings are captured as requests on WAN but not LAN ...

Show me.

[stephenw10]

I can only see it varying by source address if you have some other rule(s) in place using those.

Steve

[rebi]

@Derelict

What would be the ethical way of doing it?

Thanks!

[rebi]

@stephenw10

Nope, except the default rules all I have is 4 rules which allow OpenVPN (UDP to "This Firewall"), ICMP and HTTP/HTTPS (TCP to Reverse Proxy Internal IP) + 2 1:1 rules for the Virtual IPs.

Thanks!

[stephenw10]

If it was some sort of ARP issue I'd expect to see pfSense ARPing for the target in the LAN side pcap. But I can't see how that could happen since the internal VM is already in the table as the target for the previous forward.

You can PM the pcaps to us if you need to.

Steve

[rebi]

@stephenw10 Thank you!
I'm not sure how to send one on this particular forum software (nodebb) ... seems like there are chats instead of regular PMs which are restricted

[Derelict]

How, exactly, are the 1:1 NATs configured?

[rebi]

@Derelict

Interface External IP Internal IP Destination IP
WAN VIP1 192.168.101.2 *
WAN VIP2 192.168.101.2 *

[Derelict]

That is not 1:1 NAT. That is 2:1 NAT.

[stephenw10]

Yes. The port forwards should override that if there is some problem there but only inbound. There might still be conflicting outbound NAT causing an issue.

Try disabling the 1:1 NAT rules and using port forwards only there.

Steve

[Derelict]

Or put another address on the target server and 1:1 NAT the VIPs to their own addresses.