3Com 4210G Series, Configuration Manual, Page: 306 / 1133

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successively sent exceeds the capacity of the token bucket, the additional ICMPv6 error packets
cannot be sent out until the capacity of the token bucket is restored.
Follow these steps to configure the capacity and update interval of the token bucket:
To do… Use the command… Remarks
Enter system view
system-view
—
Configure the
capacity and
update interval of
the token bucket
Ipv6 icmp-error
{
bucket
bucket-size | ratelimit
interval
} *
Optional
By default, the capacity of a token bucket is 10
and the update interval is 100 milliseconds. That
is, at most 10 IPv6 ICMP error packets can be
sent within 100 milliseconds.
The update interval “0” indicates that the
number of ICMPv6 error packets sent is not
restricted.
Enable Sending of Multicast Echo Replies
If hosts are capable of answering multicast echo requests, Host A can attack Host B by sending an
echo request with the source being Host B to a multicast address, then all the hosts in the multicast
group will send echo replies to Host B. Therefore, to prevent such an attack, a device is disabled from
replying multicast echo requests by default.
Follow these steps to enable sending of multicast echo replies:
To do… Use the command… Remarks
Enter system view
system-view
—
Enable sending of multicast
echo replies
ipv6 icmpv6
multicast-echo-reply enable
Not enabled by default.
Enabling Sending of ICMPv6 Time Exceeded Packets
A device sends an ICMPv6 time exceeded packet in the following cases.
z
If a received IPv6 packet’s destination IP address is not the local address and its hop count is 1,
the device sends an ICMPv6 time-to-live count exceeded packet to the source.
z
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 time exceeded packet is sent to the source.
If large amounts of malicious packets are received, the performance of a device degrades greatly
because it has to send back ICMP time exceeded packets. You can disable sending of ICMPv6
time-to-live count exceeded packets.
Follow these steps to enable sending of ICMPv6 time exceeded packets:
To do… Use the command… Remarks
Enter system view
system-view
—
Enable sending of ICMPv6
time exceeded packets
ipv6 hoplimit-expires enable
Optional
Enabled by default.