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Old 12-08-2014, 05:28 AM   #1
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Registered: Dec 2014
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Forcing DF bit in ipv4

Hi I'm new to arch and I have to use it as part of a project. One of the requirements of the project is to set the DF (Don't Fragment) flag on all outgoing packets. I have tried the
sysctl -w net.ipv4.ip_no_pmtu_disc=0
method but that does not seem to work.

Any other suggestions as to how to force the DF flag on all outgoing packets?

Old 12-09-2014, 02:08 AM   #2
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Registered: Jun 2008
Location: Eelam
Distribution: Redhat, Solaris, Suse
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Hi rikkic,
1) Add as IP route
ip route add dev eth0 advmss 1500

2) Iptables
This calculates the proper MSS for your link.
# iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss 128

3) Set MTU in the ifcfg-<dev> file in /etc/sysconfig/network-scripts/

You can try any of this.


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