HP VPN Firewall Appliances Network Management Configuration Guide

693
Configuring the interface MTU
IPv6 routers do not support packet fragmentation. After an IPv6 router receives an IPv6 packet, if the
packet size is greater than the MTU of the forwarding interface, the router discards the packet.
Meanwhile, the router sends the MTU to the source host through an ICMPv6 packet — Packet Too Big
message. The source host fragments the packet according to the MTU and resends it. To reduce the extra
flow overhead resulting from packets being discarded, a proper interface MTU should be configured
according to the actual networking environment.
To configure the interface MTU:
Ste
p
Command Remarks
1. Enter system view.
system-view N/A
2. Enter interface view.
interface interface-type interface-number N/A
3. Configure the interface MTU.
ipv6 mtu mtu-size
Optional.
1500 by default.
Configuring a static path MTU for a specific IPv6 address
You can configure a static path MTU for a specific destination IPv6 address. When a source host sends
a packet through an interface, it compares the interface MTU with the static path MTU of the specified
destination IPv6 address. If the packet size is larger than the smaller one of the two values, the host
fragments the packet according to the smaller value.
To configure a static path MTU for a specific IPv6 address:
Ste
p
Command Remarks
1. Enter system view.
system-view N/A
2. Configure a static path MTU
for a specific IPv6 address.
ipv6 pathmtu [ vpn-instance
vpn-instance-name ] ipv6-address [ value ]
Not configured by
default.
Configuring the aging time for dynamic path MTUs
After the path MTU from a source host to a destination host is dynamically determined (see "Configuring
path MTU discovery"), the source host sends subsequent packets to the destination host based on this
MTU. After the aging time expires, the dynamic path MTU is removed and the source host re-determines
a dynamic path MTU through the path MTU mechanism.
The aging time is invalid for a static path MTU.
To configure the aging time for dynamic path MTUs:
Ste
p
Command Remarks
1. Enter system view.
system-view N/A
2. Configure the aging time for
dynamic path MTUs.
ipv6 pathmtu age age-time
Optional.
10 minutes by default.