I have a KVM host which bridges its eth0 as br0. I have one guest which uses the bridge adapter (rather than NAT) with its own public IP.
If I setup basic firewall rules on the host, it suddenly begins taking a long time to connect to ssh (or other services, such as http) the guest on its IP – whether locally (from the host) or from another host entirely. Long time I mean maybe 20 seconds instead of 1 second. Also its outbound connections take a long time to open as well (connecting from guest to another host).
I simply have all forwarding enabled for simplicity; without that statement no traffic is getting to or from the guest. If I flush all these rules, then connectivity returns to normal.
1. What gives?
2. How to troubleshoot further – is there a way to log all rejections?
These are my rule statements:
*filter# Allow all loopback (lo0) traffic and drop all traffic to 127/8 that doesn't use lo0 -A INPUT -i lo -j ACCEPT -A INPUT ! -i lo -d 127.0.0.0/8 -j REJECT# Accept all established inbound connections -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT# Allow all outbound traffic - you can modify this to only allow certain traffic -A OUTPUT -j ACCEPT# Forward all traffic through the bridge interface -A FORWARD -j ACCEPT# Allow HTTP and HTTPS connections from anywhere (the normal ports for websites and SSL). -A INPUT -p tcp --dport 80 -j ACCEPT -A INPUT -p tcp --dport 443 -j ACCEPT #allow check_nrpe & check_mk -A INPUT -p tcp --dport 5666 -j ACCEPT -A INPUT -p tcp --dport 6556 -j ACCEPT -A INPUT -p tcp --dport 2220 -j ACCEPT# Allow SSH connections # # The -dport number should be the same port number you set in sshd_config # -A INPUT -p tcp -m state --state NEW --dport 22 -j ACCEPT# Allow ping -A INPUT -p icmp -m icmp --icmp-type 8 -j ACCEPT# Log iptables denied calls -A INPUT -m limit --limit 5/min -j LOG --log-prefix "iptables denied: " --log-level 7# Reject all other inbound - default deny unless explicitly allowed policy -A INPUT -j REJECTCOMMIT
Did you setup the services to try to reverse DNS incoming connections (as is the default often with ssh), then proceed to block DNS queries via your firewall rules?
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