Configuring Tcp Attributes; Configuring Tcp Mss For The Interface; Enabling The Syn Cookie Feature - 3Com MSR 50 Series Configuration Manual

Configuring TCP
Attributes
Configuring TCP MSS for
the Interface
Enabling the SYN Cookie
Feature
# Configure an IP address for the interface Ethernet 1/0.
[RouterB] interface ethernet 1/0
[RouterB-Ethernet1/0] ip address 2.2.2.1 24
[RouterB-Ethernet1/0] quit
Configure the host
■
# Set the IP address of the network interface card (NIC) connected to Router A to
1.1.1.1, the subnet mask to 255.255.255.0, and the gateway address to 1.1.1.2.
After the above configurations, if you ping the subnet broadcast address
(2.2.2.255) of interface Ethernet 1/0 of Router A on the host, the ping packets can
be received by interface Ethernet 1/0 of Router B. However, if you disable the ip
forward-broadcast command, the interface Ethernet 1/0 of Router B cannot
receive the ping packets.
An interface's TCP MSS determines whether the TCP packets of the interface need
to be fragmented. If the size of a packet is smaller than the TCP MSS, the packet is
not fragmented; otherwise, it will be fragmented according to the TCP MSS.
Follow these steps to configure TCP MSS of the interface:
To do...
Enter system view
Enter interface view
Configure TCP MSS of the
interface
n
So far the interfaces that support this configuration include: Layer 3 Ethernet
interface, serial port, ATM interface, POS interface, dial port, Tunnel interface,
virtual Ethernet interface and virtual interface template.
As a general rule, the establishment of a TCP connection involves the following
three handshakes:
1 The request originator sends a SYN message to the target server.
2 After receiving the SYN message, the target server establishes a TCP
semi-connection in the SYN_RECEIVED state, returns a SYN ACK message to the
originator, and waits for a response.
3 After receiving the SYN ACK message, the originator returns an ACK message.
Thus, the TCP connection is established.
Malicious attackers may mount SYN Flood attacks during TCP connection
establishment. They send SYN messages to the server to establish TCP
connections, but they never make any response to SYN ACK messages. As a result,
Use the command...
system-view
interface interface-type
interface-number
tcp mss value

Configuring TCP Attributes

Remarks
-
-
Required
TCP MSS is 1460 bytes by
default.
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