Dropping IPv6 Fragments

Benno Overeinder benno at NLnetLabs.nl
Fri Oct 5 13:17:33 UTC 2012

On 10/04/2012 04:36 PM, Dobbins, Roland wrote:
> On Oct 4, 2012, at 9:26 PM, Sander Steffann wrote:
>> The closer you get to the edge the more common it might become...
> iACLs should be implemented at the network edge to drop all IPv4 and IPv6 traffic - including non-initial fragments - directed towards point-to-point links, loopbacks, and other internal infrastructure with exceptions made for cases where there's a legitimate need for sources outside your network to be able to communicate with your infrastructure.
> As mentioned previously on the thread, this has nothing to do with transit data-plane traffic, which should be left untouched unless it's specifically classified as attack traffic or other undesirable traffic.
> There's an apparently common misperception that fragmented traffic is somehow bad.  It isn't.  It's normal, under most circumstances.  Protect your infrastructure proactively, deal with anything else on a case-by-case basis.

Two students worked on a project in June to measure fragment dropping in
IPv6 (and IPv4) using the RIPE Atlas probe infrastructure.  Their
findings are consistent with Sander's remark.  The core seems to do
fine, but at the edges it is observed that some middleboxes/CPEs do drop
IPv6 fragments.

I think this is consistent with the remarks of Joel and Roland earlier
on Cisco/Juniper iACL vs. simpler boxes in your network.

You can find the report at


-- Benno

Benno J. Overeinder
NLnet Labs

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