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Question about gre tunnels (lemmy.goblackcat.com)
submitted 1 year ago by housepanther@lemmy.goblackcat.com to c/linux@lemmy.ml
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Hello, I have a rather complicated need to use a gre tunnel and I am having difficulty getting it working. The tunnel is between my home server and Oracle VM. Below is a picture of the topology with config.

Pings between the home server and Oracle VM over the gre tunnel do not seem to be going through as evidenced by tcpdump. I do notice however that the firewall has the correct state table showing that address translation. I am certain that both machines' firewalls are not dropping packets because iptables is not showing anything dropped. I am at a loss here so I welcome any ideas.

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[-] socphoenix@midwest.social 6 points 1 year ago

I’m unable to read the text I’m the image, can you post your firewall rules?

[-] Parodper@foros.fediverso.gal 2 points 1 year ago* (last edited 1 year ago)

I believe OP has made some mistakes when pasting the text

[Diagram]
Oracle VM: Linux
External IP: 192.0.2.1
Internal IP: 172.16.0.2
 |
 | GRE Tunnel
 v
Home Server: Linux
Internal IP: 172.16.0.2
 |
 |
 v
Firewall: FreeBSD
Internal IP: 172.16.0.1
External IP: 192.0.2.2

[Text]
Home Linux Server GRE config:
$ sudo ip tunnel add gre0 mode gre remote 172.16.0.2 local 192.0.2.1 ttl 255
$ sudo ip link set gre0 up
$ sudo ip addr add 10.100.10.1/24 dev gre0


Home Linux Server GRE config:
$ sudo ip tunnel add gre0 mode gre remote 192.0.2.2 local 192.0.2.1 ttl 255
$ sudo ip link set gre0 up
$ sudo ip addr add 10.100.10.1/24 dev gre0

Firewall:
nat on igb1 inet from ! (igb1) to any -> (igb1:0)
nat on igb0 inet proto gre from 172.16.0.2 to any -> (igb1:0)
rdr pass on igb1 inet proto gre from 141.148.84.178 to (igb1) -> 172.16.0.2
[-] tla@sopuli.xyz 1 points 1 year ago

gre implies you want to run dynamic routing over the tunnel but no routing is configured? If you don't need dynamic routing (why would you on a P2P tunnel?) but do want privacy then use IPsec or SSH instead?

this post was submitted on 27 Aug 2023
20 points (91.7% liked)

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