Werden Hosts IP-Fragmentierung durchführen?

7

Ich habe gehört, dass Router alleine fragmentieren. Wenn ein Host mit einem Ethernet-Kabel mit dem Netzwerk verbunden ist, wie bleibt die MTU-Größe bei 1500? Wird der Host selbst fragmentieren und nur 1500-Byte-Nutzdaten im Ethernet-Kabel senden?

ethernet ipv4 ipv6 protocol-theory Jinga
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Hat dir eine Antwort geholfen? Wenn ja, sollten Sie die Antwort akzeptieren, damit die Frage nicht für immer auftaucht und nach einer Antwort sucht. Alternativ können Sie Ihre eigene Antwort bereitstellen und akzeptieren.
Ron Maupin

Antworten:

8

IPv6-Fragmentierung

Nur IPv6-Hosts können fragmentieren (siehe RFC 2460 - IPv6-Spezifikation, Abschnitt 4.5 ):

4.5 Fragment Header


   The Fragment header is used by an IPv6 source to send a packet larger
   than would fit in the path MTU to its destination.  (Note: unlike
   IPv4, fragmentation in IPv6 is performed only by source nodes, not by
   routers along a packet's delivery path -- see section 5.

IPv4-Fragmentierung

IPv4 - Hosts optional kann fragmentieren (ref RFC 1122 - Internet - Host - Anforderungen, Abschnitt 3.3.3 ) und IPv4 - Router muss Fragmentierung führen.

Zitieren von RFC 1122 - Internet Host-Anforderungen, Abschnitt 3.3.3 :

3.3.3  Fragmentation

         Optionally, the IP layer MAY implement a mechanism to fragment
         outgoing datagrams intentionally.

Zitieren von RFC 1812 - IP Router-Anforderungen, Abschnitt 4.2.2.7

4.2.2.7 Fragmentation: RFC 791 Section 3.2


   Fragmentation, as described in [INTERNET:1], MUST be supported by a
   router.

Beispiel :

Es ist ziemlich einfach zu veranschaulichen, wie Hosts fragmentieren ... zum Beispiel einen Internet-Host mit einer sehr großen Ping-Größe (> 1500 Bytes) anpingen ...

In Terminal 1:

[mpenning@Bucksnort ~]$  ping -c 1 -s 65507 4.2.2.2

In Terminal 2:

[mpenning@Bucksnort ~]$ sudo tshark -n -i eth0 icmp
  1   0.000000 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=0)
  2   0.000058 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=1480)
  3   0.000071 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=2960)
  4   0.000081 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=4440)
  5   0.000094 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=5920)
  6   0.000105 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=7400)
  7   0.000116 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=8880)
  8   0.000124 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=10360)
  9   0.000133 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=11840)
 10   0.000143 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=13320)
 11   0.000152 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=14800)
 12   0.000162 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=16280)
 13   0.000172 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=17760)
 14   0.000181 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=19240)
 15   0.000191 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=20720)
 16   0.000201 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=22200)
 17   0.000211 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=23680)
 18   0.000221 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=25160)
 19   0.000230 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=26640)
 20   0.000240 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=28120)
 21   0.000250 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=29600)
 22   0.000259 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=31080)
 23   0.000269 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=32560)
 24   0.000278 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=34040)
 25   0.000288 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=35520)
 26   0.000298 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=37000)
 27   0.000308 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=38480)
 28   0.000318 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=39960)
 29   0.000327 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=41440)
 30   0.000337 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=42920)
 31   0.000352 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=44400)
 32   0.000361 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=45880)
 33   0.000372 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=47360)
 34   0.000384 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=48840)
 35   0.000394 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=50320)
 36   0.000403 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=51800)
 37   0.000411 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=53280)
 38   0.000419 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=54760)
 39   0.000428 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=56240)
 40   0.000437 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=57720)
 41   0.000446 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=59200)
 42   0.000455 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=60680)
 43   0.000466 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=62160)
 44   0.000477 192.0.2.3 -> 4.2.2.2 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=63640)
 45   0.000486 192.0.2.3 -> 4.2.2.2 ICMP Echo (ping) request
 46   0.044402 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=0)
 47   0.044439 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=1480)
 48   0.044899 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=2960)
 49   0.044910 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=4440)
 50   0.044916 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=5920)
 51   0.045149 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=7400)
 52   0.045399 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=8880)
 53   0.045409 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=10360)
 54   0.045415 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=11840)
 55   0.045649 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=13320)
 56   0.045899 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=14800)
 57   0.045908 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=16280)
 58   0.045915 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=17760)
 59   0.046148 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=19240)
 60   0.046163 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=20720)
 61   0.046402 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=22200)
 62   0.046421 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=23680)
 63   0.046650 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=25160)
 64   0.046668 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=26640)
 65   0.046901 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=28120)
 66   0.046918 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=29600)
 67   0.047151 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=31080)
 68   0.047171 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=32560)
 69   0.047399 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=34040)
 70   0.047418 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=35520)
 71   0.047424 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=37000)
 72   0.047650 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=38480)
 73   0.047900 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=39960)
 74   0.048149 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=41440)
 75   0.048165 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=42920)
 76   0.048172 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=44400)
 77   0.048178 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=45880)
 78   0.048398 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=47360)
 79   0.048650 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=48840)
 80   0.048667 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=50320)
 81   0.048674 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=51800)
 82   0.048900 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=53280)
 83   0.048922 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=54760)
 84   0.049150 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=56240)
 85   0.049174 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=57720)
 86   0.049398 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=59200)
 87   0.049649 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=60680)
 88   0.049671 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=62160)
 89   0.049677 4.2.2.2 -> 192.0.2.3 IP Fragmented IP protocol (proto=ICMP 0x01, 
   off=63640)
 90   0.049683 4.2.2.2 -> 192.0.2.3 ICMP Echo (ping) reply
Mike Pennington
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Die meisten modernen Betriebssysteme führen die IPv4-Pfad-MTU-Erkennung durch und setzen daher das Flag "Nicht fragmentieren" auf alle ausgehenden Pakete.
BatchyX
Also, wenn auf dem Host., Wenn ich ein sehr großes Paket pinge, fragmentiert es zum Standard-Gateway?
Jinga
1
@BatchyX, die Frage ist nicht, ob Hosts PMTUD ausführen, sondern ob sie fragmentieren können.
Mike Pennington
@Jinga, das ist richtig; Wenn Sie mit einer großen Ping-Größe pingen und eine Fragmentierung anfordern, wird der Ping in die MTU Ihres lokalen Links fragmentiert.
Mike Pennington
2
@BatchyX, PMTUD kommt hier nicht in Frage. Zu Ihrer Information, meine Linux-Server rufen den ganzen Tag mit SNMP ab und DF ist für diese UDP-Frames nicht festgelegt. Daher ist Ihre Aussage, dass DF für alle Frames festgelegt wird, offensichtlich falsch. Bitte hören Sie auf, das Problem mit irrelevanten PMTUD-Informationen zu verwechseln.
Mike Pennington