Setting Mtu For An Interface; Setting Tcp Mss For An Interface; Configuring Tcp Path Mtu Discovery - HPE FlexNetwork MSR Series Comware 7 Layer 3 - Ip Services Configuration Manuals

Setting MTU for an interface

When a packet exceeds the MTU of the output interface, the device processes it in one of the
following ways:
•
If the packet disallows fragmentation, the device discards it.
•
If the packet allows fragmentation, the device fragments it and forwards the fragments.
Fragmentation and reassembling consume system resources, so set the appropriate MTU for an
interface based on the network environment to avoid fragmentation.
To set the MTU for an interface:
Step
1. Enter system view.
2. Enter interface view.
3. Set the MTU for the interface.

Setting 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 set the 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 set the
TCP MSS on the interface.
To set the TCP MSS for the interface:
Step
1. Enter system view.
2. Enter interface view.
3. Set the TCP MSS for the
interface.

Configuring TCP path MTU discovery

IMPORTANT:
All 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 1191) discovers the path MTU between the source and destination
ends of a TCP connection. It works as follows:
Command
system-view
interface interface-type
interface-number
ip mtu mtu-size
Command
system-view
interface interface-type
interface-number
tcp mss value
210
Remarks
N/A
N/A
By default, the MTU is not set.
Remarks
N/A
N/A
By default, the TCP MSS is not set.