Networking: View PMTUD cache on linux

ip route show cache

ip route show cache <ip>

Wireshark shows packets larger than MTU

TCP segment of a reassembled PDU

wireshark shows a frame with 2574 Bytes,
tcpdump shows the same frame as 2574 Bytes

A very good post:
http://sandilands.info/sgordon/segmentation-offloading-with-wireshark-and-ethtool

and you are sure that the MTU is 1500 or lower (no jumbo frames), since you saw the MSS in the SYN and SYN/ACK, so both sides are certainly below 1500.

Apparently this is because of the NIC doing tcp segmentation offloading:


 # ethtool -k eth0
Offload parameters for eth0:
rx-checksumming: on
tx-checksumming: on
scatter-gather: on
tcp-segmentation-offload: on
udp-fragmentation-offload: off
generic-segmentation-offload: on
generic-receive-offload: off
large-receive-offload: on

ethtool -K eth0 tso off
ethtool -K eth0 gso off

I turned off tcp first but the generic did prevail so I turned off gso and thought I saw only smaller packages but when enabling and disabling it again I did not see the small packets anymore, so maybe a restart is necessary.

Would be nice to see it working or not the 2nd time you disable it. But I won't restart the system.

Networking: MTU

http://www.elifulkerson.com/projects/mturoute.php

Networking: MTU MSS PMTUD

http://packetlife.net/blog/2008/aug/18/path-mtu-discovery/

http://www.nil.si/ipcorner/IP_Fragmentation

http://www.cisco.com/en/US/tech/tk827/tk369/technologies_white_paper09186a00800d6979.shtml

Networking: Troubleshooting: MTU with ping -l 1472 -f

windows:
ping -f -l 1472 destIP


linux:
ping -M do -s 1472 -c 1 destIP

linux: fat32 bootable usb stick with ESXi

http://pubs.vmware.com/vsphere-50/index.jsp?topic=%2Fcom.vmware.vsphere.install.doc_50%2FGUID-33C3E7D5-20D0-4F84-B2E3-5CD33D32EAA8.html

linux: ubuntu: map c drive from a windows machine over the network

Start Nautilus, i.e. click on the home folder icon.

Press CTRL-L (for location) and enter smb://<ip or name>/share, e.g. smb://10.0.0.1/c$

It will then ask for domain, username and password

linux: ubuntu: change keyboard mapping from terminal

setxkbmap fr


http://wiki.laptop.org/go/Keyboard_Files

linux: multiple default gateways (even for aliases)

A really great blog entry, which solved all my issues in no time. The only thing is now that I have multiple distributions and have to find out where to place the commands so that after a reboot it will come back correctly.

http://kindlund.wordpress.com/2007/11/19/configuring-multiple-default-routes-in-linux/

linux: alias

ifconfig eth0:0 10.0.0.2 netmask 255.255.255.0 up

ifconfig eth0:0 10.0.0.2 netmask 255.255.255.0 down