{{tag>Brouillon Réseau}}

= Notes TCP/IP Jumbo Frame Trame géante MTU

Voir : 
* [[https://fr.wikipedia.org/wiki/Trame_g%C3%A9ante|Jumbo Frame]]
* 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
<code bash>
netstat -i
ip link |grep mtu
</code>

Changer provisoirement la MTU d'une inferface
<code bash>
#ifconfig eth1 mtu 9000 up
ip link set eth1 mtu 9000
</code>


Changer la MTU sur RedHat

''/etc/sysconfig/network-scripts/ifcfg-enp0s9''
<code 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
</code>

Changer la MTU sous RedHat avec NetworkManager
<code bash>
nmcli connection modify eno2 802-3-ethernet.mtu 9000
nmcli connection show eno2 |grep mtu
</code>


Changer la MTU d'une interface sur Debian

''/etc/network/interfaces.d/eth1''
<code ->
auto eth1

iface eth1 inet static
        address 192.168.56.12
        netmask 255.255.255.0
        mtu 9000
</code>

Appliquer les changements
<code bash>
systemctl restart networking
</code>

Connaitre la MTU entre deux points
<code ->
# traceroute --mtu 192.168.56.1

traceroute to 192.168.56.1 (192.168.56.1), 30 hops max, 65000 byte packets
 1  192.168.56.1 (192.168.56.1)  0.223 ms F=1500 *  0.446 ms
</code>

**F=1500**

== Tester

** 1472 = 1500 - 28 **

Voir aussi ''/proc/sys/net/ipv4/ip_no_pmtu_disc''

<code ->
# ping -M do -s 1472 192.168.6.130
PING 192.168.6.130 (192.168.6.130) 1472(1500) bytes of data.
1480 bytes from 192.168.6.130: icmp_req=1 ttl=255 time=0.095 ms
1480 bytes from 192.168.6.130: icmp_req=2 ttl=255 time=0.127 ms
^C
--- 192.168.6.130 ping statistics ---
2 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 ---
4 packets transmitted, 0 received, 100% packet loss, time 2999ms
</code>


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.

<code bash>
ip route flush cache
</code>