av peterh » 2020-03-12 15:19
Ett exempel på hur man tar reda på största tillåtna mtu mellan 2 noder. det bortre "exempel.helge"
Lokala interfacet ser ut så här i denna burk :
en1: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1460
ether d8:bb:2c:bb:43:fe
inet6 fe80::1c56:ee95:4e4b:86af%en1 prefixlen 64 secured scopeid 0x8
inet 192.168.68.109 netmask 0xffffff00 broadcast 192.168.68.255
nd6 options=201<PERFORMNUD,DAD>
media: autoselect
status: active
Dvs MTU = 1460
Ping kommandot i en fullvuxen implementation har switchar för
-paketstorlek ‘-s’
-antal ping ‘-c’
-Set don’f fragment ‘-D’
Se nedan ping —help
usage: ping [-AaDdfnoQqRrv] [-c count] [-G sweepmaxsize]
[-g sweepminsize] [-h sweepincrsize] [-i wait]
[-l preload] [-M mask | time] [-m ttl] [-p pattern]
[-S src_addr] [-s packetsize] [-t timeout][-W waittime]
[-z tos] host
ping [-AaDdfLnoQqRrv] [-c count] [-I iface] [-i wait]
[-l preload] [-M mask | time] [-m ttl] [-p pattern] [-S src_addr]
[-s packetsize] [-T ttl] [-t timeout] [-W waittime]
[-z tos] mcast-group
Apple specific options (to be specified before mcast-group or host like all options)
-b boundif # bind the socket to the interface
-k traffic_class # set traffic class socket option
-K net_service_type # set traffic class socket options
-apple-connect # call connect(2) in the socket
-apple-time # display current time
Genom att sända paket med ökande storlek samtidigt som man
förbjuder fragmentering kan man få reda på största möjliga mtu :
--- exempel.helge ping statistics ---
1 packets transmitted, 1 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 11.882/11.882/11.882/0.000 ms
[MacBook-Pro:~] peter% ping -s 1430 -D -c 1 exempel.helge
PING exempel.helge (212.85.78.142): 1430 data bytes
1438 bytes from 212.85.78.142: icmp_seq=0 ttl=249 time=11.531 ms
--- exempel.helge ping statistics ---
1 packets transmitted, 1 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 11.531/11.531/11.531/0.000 ms
[MacBook-Pro:~] peter% ping -s 1431 -D -c 1 exempel.helge
PING exempel.helge (212.85.78.142): 1431 data bytes
1439 bytes from 212.85.78.142: icmp_seq=0 ttl=249 time=15.457 ms
--- exempel.helge ping statistics ---
1 packets transmitted, 1 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 15.457/15.457/15.457/0.000 ms
[MacBook-Pro:~] peter% ping -s 1432 -D -c 1 exempel.helge
PING exempel.helge (212.85.78.142): 1432 data bytes
1440 bytes from 212.85.78.142: icmp_seq=0 ttl=249 time=9.256 ms
--- exempel.helge ping statistics ---
1 packets transmitted, 1 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 9.256/9.256/9.256/0.000 ms
[MacBook-Pro:~] peter% ping -s 1433 -D -c 1 exempel.helge
PING exempel.helge (212.85.78.142): 1433 data bytes
ping: sendto: Message too long
Så i detta exempel är det inte nätverket mellan lokala noden och destinationen som sätter gränserna
Så här ser en traceroute ut i samma exempel :
traceroute to n.manet.nu (212.85.78.142), 64 hops max, 52 byte packets
1 192.168.68.1 (192.168.68.1) 4.732 ms 1.431 ms 1.009 ms
2 * * *
3 * * *
4 213.67.13.150 (213.67.13.150) 6.054 ms 2.616 ms 3.079 ms
5 g-br-sec1-link.se.telia.net (81.228.86.207) 8.420 ms 8.583 ms
g-br-sec1-link.se.telia.net (81.228.86.205) 8.427 ms
6 telia-bahnhof-pni-gbg.bahnhof.net (46.59.116.193) 8.080 ms 8.081 ms 7.752 ms
7 gbg-cr3.gbg-shg-dr3.bahnhof.net (176.10.180.136) 9.775 ms 8.511 ms 8.625 ms
8 exempel.helge (xxx.xx.xx.145) 9.671 ms 8.279 ms 9.307 ms
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