Brocade Virtual ADX Security Guide (Supporting ADX v03.1.00) - Manual (Page 79)

Brocade Virtual ADX Security Guide 67
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Translation timeouts
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Translation timeouts
The NAT translation table contains all the currently active NAT translation entries on the device. An
active entry is one the Brocade Virtual ADX creates for a private address when the client at that
address sends traffic.
NAT performs the following steps to provide an address translation for a source IP address:
• NAT looks in the translation table for an active NAT entry for the translation. If the table
contains an active entry for the session, the Brocade Virtual ADX uses that entry.
• If NAT does not find an active entry in the NAT translation table, NAT creates an entry and
places the entry in the table. The entry remains in the table until the entry times out.
Each NAT entry remains in the translation table until the entry ages out.
After the configuration of a NAT timeout the following occurs:
• Existing entries of the modified protocol remain in the translation table.
• If existing session entries send or receive packets then the timeout value is updated to the new
configured value.
• If existing session entries do not process any traffic they will continue to age out in accordance
with the old timeout value.
• When the timeout (age of the session) expires, forward and reverse sessions in the Brocade
Virtual ADX are deleted with no further actions. If traffic is received on this flow the Brocade
Virtual ADX drops the packets because it will not find sessions related to that particular flow.
Configuring the NAT translation aging timer
Use the ip nat translation command to alter the NAT translation aging timer.
The NAT translation table contains all the currently active NAT translation entries on the device. An
active entry is one that the Brocade Virtual ADX created for a private address when that client at
that address sent traffic to the Internet. NAT performs the following steps to provide an address
translation for a source IP address:
• The feature looks in the NAT translation table for an active NAT entry for the translation. If the
table contains an active entry for the session, the Brocade Virtual ADX uses that entry.
• If NAT does not find an active entry in the NAT translation table, NAT creates an entry and
places the entry in the table. The entry remains in the table until the entry times out.
Virtual ADX(config)#ip nat translation tcp-timeout 1800
Syntax: [no] ip nat translation dns-timeout | finrst-timeout | icmp-timeout | syn-timeout |
tcp-timeout | udp-timeout secs maximum
Syntax: [no] ip nat translation max-entries number-of-entries
The dns-timeout keyword indicates connections to a Domain Name Server (DNS). The default is
120 seconds.
The finrst-timeout keyword identifies TCP FIN (finish) and RST (reset) packets, which normally
terminate TCP connections. The default is 120 seconds. This timer is not related to tcp-timeout,
which applies to packets to or from a host address that is mapped to an global IP address and a
TCP port number (PAT feature). The finrst-timeout applies to packets that terminate a TCP session,
regardless of the host address or whether PAT is used.