[e2e] ICMP & TCP segments with IP ID = 0?

Richard Wendland richard at starburst.demon.co.uk
Wed May 16 10:54:12 PDT 2001

> Linux-2.3 set ip id to 0 on packets with DF, because it is undefined there.
> Do you really think it is illegal? 8)

Even if not illegal, I suspect it would be unwise in practice to not use
a real IP ID even if DF is set.  This is because I suspect some devices
remove DF "in the network" - that's evil (arguably?) but it could happen
in the wild.  I strongly suspect some HTTP load balancing devices do this,
possibly simply because they do not want to be bothered with routing ICMP
"fragmentation needed" back to the web server servicing that request.

These HTTP load balancing devices are widely used.

[I suppose it could be argued that if a device insists on clearing DF
it should create a fresh IP ID, but I don't think these devices do that.]

Richard Wendland				richard at wendland.org.uk

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