2e6d0815b2
RFC 1191
When a router is unable to forward a datagram because it exceeds the
MTU of the next-hop network and its Don't Fragment bit is set, the
router is required to return an ICMP Destination Unreachable message
to the source of the datagram, with the Code indicating
"fragmentation needed and DF set". To support the Path MTU Discovery
technique specified in this memo, the router MUST include the MTU of
that next-hop network in the low-order 16 bits of the ICMP header
field that is labelled "unused" in the ICMP specification [7]. The
high-order 16 bits remain unused, and MUST be set to zero. Thus, the
message has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 3 | Code = 4 | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| unused = 0 | Next-Hop MTU |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Internet Header + 64 bits of Original Datagram Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
RFC 1185
Packet Too Big Message
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MTU |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| As much of invoking packet |
+ as will fit without the ICMPv6 packet +
| exceeding 576 octets |
IPv6 Fields:
Destination Address
Copied from the Source Address field of the invoking
packet.
ICMPv6 Fields:
Type 2
Code 0
MTU The Maximum Transmission Unit of the next-hop link.
Description
A Packet Too Big MUST be sent by a router in response to a packet
that it cannot forward because the packet is larger than the MTU of
the outgoing link. The information in this message is used as part
of the Path MTU Discovery process [RFC-1191].
Signed-off-by: wangchen <wangchen41@xiaomi.com>
119 lines
3.5 KiB
C
119 lines
3.5 KiB
C
/****************************************************************************
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* net/icmp/icmp_pmtu.c
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <sys/time.h>
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#include <nuttx/clock.h>
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#include "icmp/icmp.h"
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#include "utils/utils.h"
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/****************************************************************************
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* Private Data
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****************************************************************************/
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static struct icmp_pmtu_entry
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g_icmp_pmtu_entry[CONFIG_NET_ICMP_PMTU_ENTRIES];
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: icmpv4_find_pmtu_entry
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*
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* Description:
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* Search for a ipv4 destination cache entry
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*
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* Parameters:
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* destipaddr the IPv4 address of the destination
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*
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* Return:
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* not null is success; null is failure
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****************************************************************************/
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FAR struct icmp_pmtu_entry *icmpv4_find_pmtu_entry(in_addr_t destipaddr)
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{
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clock_t now = clock_systime_ticks();
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int i;
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for (i = 0; i < CONFIG_NET_ICMP_PMTU_ENTRIES; i++)
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{
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if (g_icmp_pmtu_entry[i].pmtu == 0)
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{
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continue;
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}
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if (net_ipv4addr_cmp(destipaddr, g_icmp_pmtu_entry[i].daddr))
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{
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g_icmp_pmtu_entry[i].time = now;
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return &g_icmp_pmtu_entry[i];
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}
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}
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return NULL;
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}
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/****************************************************************************
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* Name: icmpv4_add_pmtu_entry
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*
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* Description:
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* Create a new ipv4 destination cache entry. If no unused entry is found,
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* will recycle oldest entry
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*
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* Parameters:
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* destipaddr the IPv4 address of the destination
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* mtu MTU
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*
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* Return:
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* void
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****************************************************************************/
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void icmpv4_add_pmtu_entry(in_addr_t destipaddr, int mtu)
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{
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clock_t now = clock_systime_ticks();
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int j = 0;
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int i;
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for (i = 0; i < CONFIG_NET_ICMP_PMTU_ENTRIES; i++)
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{
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if ((g_icmp_pmtu_entry[i].pmtu == 0) ||
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(sclock_t)(now - g_icmp_pmtu_entry[i].time) >=
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SEC2TICK(CONFIG_NET_ICMP_PMTU_TIMEOUT * 60))
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{
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j = i;
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break;
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}
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if ((sclock_t)(g_icmp_pmtu_entry[i].time -
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g_icmp_pmtu_entry[j].time) < 0)
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{
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j = i;
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}
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}
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net_ipv4addr_copy(g_icmp_pmtu_entry[j].daddr, destipaddr);
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g_icmp_pmtu_entry[j].pmtu = mtu;
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g_icmp_pmtu_entry[j].time = now;
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}
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