H3C Technologies H3C S10500 Series Switches - Manual (Page 131)

120
• Upon receiving the first fragment of an IPv6 datagram with the destination IP address being the
local address, the device starts a timer. If the timer expires before all the fragments arrive, an
ICMPv6 Fragment Reassembly Timeout message is sent to the source.
If large quantities of malicious packets are received, the performance of a device degrades greatly
because it must send back ICMP Time Exceeded messages. You can disable sending of ICMPv6 Time
Exceeded messages.
Follow these steps to enable sending of ICMPv6 time exceeded messages:
To do… Use the command… Remarks
Enter system view system-view —
Enable sending of ICMPv6 Time
Exceeded messages
ipv6 hoplimit-expires enable
Optional
Enabled by default.
Enabling sending of ICMPv6 destination unreachable
messages
If the device fails to forward a received IPv6 packet because of one of the following reasons, it drops the
packet and sends a corresponding ICMPv6 Destination Unreachable error message to the source.
• If no route is available for forwarding the packet, the device sends a "no route to destination"
ICMPv6 error message to the source.
• If the device fails to forward the packet because of an administrative prohibition (such as a firewall
filter or an ACL), the device sends the source a "destination network administratively prohibited"
ICMPv6 error message.
• If the device fails to deliver the packet because the destination is beyond the scope of the source
IPv6 address (for example, the source IPv6 address of the packet is a link-local address whereas the
destination IPv6 address of the packet is a global unicast address), the device sends the source a
"beyond scope of source address" ICMPv6 error message.
• If the device fails to resolve the corresponding link layer address of the destination IPv6 address, the
device sends the source an "address unreachable" ICMPv6 error message.
• If the packet with the destination being local and transport layer protocol being UDP and the
packet’s destination port number does not match the running process, the device sends the source
a "port unreachable" ICMPv6 error message.
If an attacker sends abnormal traffic that causes the device to generate ICMPv6 destination unreachable
messages, end users may be affected. To prevent such attacks, you can disable the device from sending
ICMPv6 destination unreachable messages.
Follow these steps to enable sending of ICMPv6 destination unreachable messages:
To do… Use the command… Remarks
Enter system view system-view —
Enable sending of ICMPv6 destination
unreachable messages
ipv6 unreachables enable
Required
Disabled by default.