Partial vs Full tables

William Herrin bill at
Wed Jun 10 23:18:03 UTC 2020

On Wed, Jun 10, 2020 at 3:02 PM Baldur Norddahl
<baldur.norddahl at> wrote:
> Am I correct in assuming loose mode RPF only drops packets from unannounced address space in the global routing table?

Actually, I'm not sure since my plan around RPF is "10 foot pole." Is
"loose mode" really just filtering packets the current routing table
deems to be bogons? If it's not tied in any way to the actual routing
paths then it seems poorly named.

> And the downside of doing so is that sometimes we do receive packets from that address space, usually back scatter from traceroute or other ICMP messages.

Those "other" ICMP messages are kinda important since TCP fails if
they're discarded. If it's just a bogon filter then by definition only
simplex communications can be impacted since there's known to be no
way for duplex communication to occur. PMTUD and traceroute responses
are examples: a router telling a host information but expecting no
response. SNMP traps are simplex though it's not obvious to me how
that would matter here. What else can you think of that's simplex?

Bill Herrin

William Herrin
bill at

More information about the NANOG mailing list