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--- tech:notes_tcp_ip_jumbo_frame_trame_geante_mtu [2025/11/11 19:48] – Jean-Baptiste
+++ tech:notes_tcp_ip_jumbo_frame_trame_geante_mtu [2026/06/07 19:12] (Version actuelle) – modification externe 127.0.0.1
@@ Ligne 1: / Ligne 1: @@
+<!DOCTYPE markdown>
+{{tag>Brouillon Réseau}}
+# Notes TCP/IP Jumbo Frame Trame géante MTU
+Voir :
+* [Jumbo Frame](https://fr.wikipedia.org/wiki/Trame_g%C3%A9ante)
+* http://www.microhowto.info/howto/change_the_mtu_of_a_network_interface.html
+Peut être utile pour du SAN / NAS :
+* [[Notes SAN iSCSI]]
+* [[Notes NFS]]
+Connaître la MTU d'une interface
+~~~bash
+netstat -i
+ip link | grep mtu
+~~~
+Changer provisoirement la MTU d'une inferface
+~~~bash
+#ifconfig eth1 mtu 9000 up
+ip link set eth1 mtu 9000
+~~~
+Changer la MTU sur RedHat
+`/etc/sysconfig/network-scripts/ifcfg-enp0s9`
+~~~ini
+HWADDR=08:00:27:D9:8B:E7
+TYPE=Ethernet
+BOOTPROTO=none
+IPADDR=192.168.25.21
+PREFIX=24
+DEFROUTE=yes
+IPV4_FAILURE_FATAL=yes
+IPV6INIT=no
+NAME=enp0s9
+UUID=5f82629e-5117-4d41-902d-090d82053cb2
+ONBOOT=yes
+MTU=9000
+~~~
+Changer la MTU sous RedHat avec NetworkManager
+~~~bash
+nmcli connection modify eno2 802-3-ethernet.mtu 9000
+nmcli connection show eno2 | grep mtu
+~~~
+Changer la MTU d'une interface sur Debian
+`/etc/network/interfaces.d/eth1`
+~~~
+auto eth1
+iface eth1 inet static
+        address 192.168.56.12
+        netmask 255.255.255.0
+        mtu 9000
+~~~
+Appliquer les changements
+~~~bash
+systemctl restart networking
+~~~
+Connaitre la MTU entre deux points
+~~~
+# traceroute --mtu 192.168.56.1
+traceroute to 192.168.56.1 (192.168.56.1), 30 hops max, 65000 byte packets
+  192.168.56.1 (192.168.56.1)  0.223 ms F=1500 *  0.446 ms
+~~~
+**F=1500**
+## Tester
+** 1472 = 1500 - 28 **
+Voir aussi `/proc/sys/net/ipv4/ip_no_pmtu_disc`
+~~~
+# ping -M do -s 1472 192.168.6.130
+PING 192.168.6.130 (192.168.6.130) 1472(1500) bytes of data.
+bytes from 192.168.6.130: icmp_req=1 ttl=255 time=0.095 ms
+bytes from 192.168.6.130: icmp_req=2 ttl=255 time=0.127 ms
+^C
+--- 192.168.6.130 ping statistics ---
+packets transmitted, 2 received, 0% packet loss, time 999ms
+rtt min/avg/max/mdev = 0.095/0.111/0.127/0.016 ms
+# ping -M do -s 1473 192.168.6.130
+PING 192.168.6.130 (192.168.6.130) 1473(1501) bytes of data.
+^C
+--- 192.168.6.130 ping statistics ---
+packets transmitted, 0 received, 100% packet loss, time 2999ms
+~~~
+Path MTUs are recorded in the routing cache. This can interfere with testing, and in particular, can make a remote MTU restriction appear to be a local one. You can clear the cache using the ip route command.
+~~~bash
+ip route flush cache
+~~~