Brocade Communications Systems 12.4.00a Hierarchy of operation, Setting the MSS value at the global level, Setting the MSS value at the virtual server level

118 ServerIron ADX Security Guide
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Configuring Syn-Proxy
5
•Virtual server lever – configures the TCP MSS value for all virtual ports under a specified virtual
server
•Virtual port level – configures the TCP MSS value for a specified virtual port
•Destination IP – configures the TCP MSS value for pass-through traffic to a specified
destination IP address
NOTE
tcp-mss will work when syn-proxy is enabled. If syn-proxy is turned off, tcp-mss will not take effect.
If the configured mininum MSS is larger than the client's actual MSS value, the ServerIron ADX will
use the client's MSS value in SYN-ACK.
Hierarchy of operation
When multiple levels of the minimum MSS value are configured, the MSS value used by the
ServerIron ADX is determined by the following hierarchy.
1. Virtual Port Level – Values configured at this level take precedence over any other MSS setting
on the ServerIron ADX.
2. Virtual Server level – Only values configured at the Virtual Port level take precedence over MSS
values configured at this level.
3. Global level – Values configured at this level take effect over all SYN-ACK packets generated by
a ServerIron ADX unless the MSS value is configured at one of the levels previous described in
1, 2 or 3.
Setting the MSS value at the global level
To globally set the MSS value for all SYN-ACK packets generated by a ServerIron ADX, use the
following command:
ServerIronADX(config)# tcp-mss 128
Syntax: [no] tcp-mss <mss-value>
The <mss-value> variable specifies MSS value for all SYN-ACK packets generated by the ServerIron
ADX regardles s of the clien t’s MSS valu e. This value can be from 64 to 9216. Make sure that the IP
MTU of the interfaces is always greater than the MSS value.
NOTE
When tcp-mss is configured at the global level, the same value will work for both IPv4 traffic and IPv6
traffic.
Setting the MSS value at the virtual server level
To set the MSS value for all of the ports under a virtual server on a ServerIron ADX, use the
following command:
ServerIronADX(config)# server virtual-name-or-ip v1
ServerIronADX(config-vs-v1)# tcp-mss 128
Syntax: [no] tcp-mss <mss-value>