bossk wrote:
Hi,
I have the following setup
------- ---------------- ----------------- ------------- ----------------
| B |--------| VPN-GW2 |=======| VPN-GW1 | --------| GW |--------| A |
------- ----------------- ------------------ ------------- ----------------
The server GW is in the same net (10.0.1.0/28) as VPN-GW via interface bond0 and connected to the same network (10.0.3.0/24) as server A with interface bond2.
Server A can send packets to server B which can be reached through the VPN.
Now the tricky part if server A sends a packet with a size of 1460 Bytes the VPN-GW1 sends an ICMP fragmentation-needed packet to A which
is not passing the GW, if the FORWARD policy is set to DROP.
I have enabled the following rules
iptables -A FORWARD -i bond0 -o bond2 -j ACCEPT
iptables -A FORWARD -i bond2 -o bond0 -j ACCEPT
and specials rules
iptables -A FORWARD -s 10.0.1.0/28 -d 10.0.3.0/24 -j ACCEPT
iptables -A FORWARD -s 10.0.3.0/24 -d 10.0.1.0/28 -j ACCEPT
If I set the FORWARD policy to ACCEPT then the ICMP fragmentation-needed packet is passing the GW. After I change the FORWARD policy to DROP
that packet is not passing the GW.
Has someone an idea why this happens?
Just a guess, but has VPN-GW1 an IP not in those ranges? Then the icmp
errors have a different source address and are logically dropped. Adding
a rule allowing RELATED traffic in should do the tric, or if you don't
use conntrack, create an explicit rule for these packets.
HTH,
M4
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