Configuring Tcp Mss For An Interface; Configuring Tcp Path Mtu Discovery - HP 6125XLG Layer 3-Ip Services Configuration Manual

Step
3. Configure an MTU for the
interface.

Configuring TCP MSS for an interface

The maximum segment size (MSS) option informs the receiver of the largest segment that the sender can
accept. Each end announces its MSS during TCP connection establishment. If the size of a TCP segment
is smaller than the MSS of the receiver, TCP sends the TCP segment without fragmentation. If not, it
fragments the segment according to the receiver's MSS.
If you configure a TCP MSS on an interface, the size of each TCP segment received or sent on the
interface cannot exceed the MSS value.
This configuration takes effect only for TCP connections established after the configuration rather than the
TCP connections that already exist.
This configuration is effective only for IP packets. If MPLS is enabled on the interface, do not configure the
TCP MSS on the interface.
To configure a TCP MSS of the interface:
Step
1. Enter system view.
2. Enter interface view.
3. Configure a TCP MSS for the
interface.

Configuring TCP path MTU discovery

IMPORTANT:
All the devices on a TCP connection must be enabled to send ICMP error messages by using the ip
unreachables enable command.
TCP path MTU discovery (in RFC 1 191) discovers the path MTU between the source and destination ends
of a TCP connection. It works as follows:
1. A TCP source device sends a packet with the Don't Fragment (DF) bit set.
2. A router that fails to forward the packet because it exceeds the MTU on the outgoing interface
discards the packet and returns an ICMP error message, which contains the MTU of the outgoing
interface.
Command
ip mtu mtu-size
Command
system-view
interface interface-type
interface-number
tcp mss value
122
Remarks
By default, no MTU is configured.
The MTU configured for an
interface takes effect on only
packets that are sent to the CPU
for software forwarding,
including packets sent from or
destined for this interface.
Remarks
N/A
N/A
By default, no TCP MSS is configured.