If I recall correctly, the base address of a subnet was originally used as an
alternative broadcast address by some ancient equipment. While it's not a
behavior I'd expect to see actively used in modern equipment, seeing it
handled as a special case as a receiver doesn't surprise me.
Based on this, it looks like it's handled as a directed broadcast:
https://www.juniper.net/techpubs/en_US/junose10.3/information-products/topic-collections/swconfig-ip-ipv6/id-25742.html
Frank Sweetser fs at wpi.edu | For every problem, there is a solution that
Manager of Network Operations | is simple, elegant, and wrong.
Worcester Polytechnic Institute | - HL Mencken
On 08/25/2015 05:45 AM, Saku Ytti wrote:
On (2015-08-24 18:38 +0000), Michael Hare wrote:
Hey,
Sorry if this is remedial, but are packets sent to the base address of a
directly connected subnet always punted to RE and if so, why? Historic
compatibility? I couldn't determine any bucket under the ddos-protection
protocol statistics such traffic ends up in, either. I haven't seen any
negative side effects of this, only noticing this after I followed up on a high
pps drop rate for one of our routing engines. This seems to happen regardless
of what I have 'targeted-broadcast' configured with [absent, forward-only].
Terrific question, I don't know, I don't think there is any real reason why
those need to be punted.
It's probably something people have done in their IP implementation and it has
just carried over in fear of changing the behaviour might break something, and
almost certainly someone now relies on this behaviour for what ever strange
reasons.
Pretty sure you'll see them in ddos-protection in what ever protocol the
traffic is, ddos-protection would not care about your DADDR, because decision
to punt was done before ddos-protection got the frame.
For what it's worth, the above is an MX104, but I also see this on other MX MPC
hardware.
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