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.
Questions: 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 REJECT
COMMIT
