Книга: Iptables Tutorial 1.2.2
In certain cases, the conntrack machine does not know how to handle a specific protocol. This happens if it does not know about that protocol in particular, or doesn't know how it works. In these cases, it goes back to a default behavior. The default behavior is used on, for example, NETBLT, MUX and EGP. This behavior looks pretty much the same as the UDP connection tracking. The first packet is considered NEW, and reply traffic and so forth is considered ESTABLISHED.
When the default behavior is used, all of these packets will attain the same default timeout value. This can be set via the /proc/sys/net/ipv4/netfilter/ip_ct_generic_timeout variable. The default value here is 600 seconds, or 10 minutes. Depending on what traffic you are trying to send over a link that uses the default connection tracking behavior, this might need changing. Especially if you are bouncing traffic through satellites and such, which can take a long time.
- TCP connections
- UDP connections
- ICMP connections
- Untracked connections and the raw table
- Setting up default policies
- Booting into the Default Runlevel
- Booting to a Nondefault Runlevel with GRUB
- Count the Number of Connections
- Displaying Connections
- mode and default
- Reject Newsfeed Connections
- Allow Newsfeed Connections