Re: [babel] Mirja Kühlewind's Discuss on draft-ietf-babel-hmac-08: (with DISCUSS and COMMENT)

[Juliusz Chroboczek <[e-mail]>]

> Sorry I mean 300ms… (one important letter).

Ah, ok.  I think I undestand what you mean now.

> But this is usually send every 4 seconds or so…?

Not necessarily.  The timers are configurable, and there can be multiple
packets sent over a single hello interval (e.g. when the routing table
doesn't fit in a single packet).  The rate limiting here is going to limit
how fast we can acquire new neighbours in the presence of packet loss.
The value 300ms was chosen as being a compromise between the amount of
traffic an attacker can cause with replayed packets, and the hard limit it
imposes on neighbour acquisition in the presence of packet loss.

This has nothing to do with congestion control, Mirja, it's solely about
resistance to DoS.  In normal operation (with no evil attacker replaying
massive numbers of packets and in the absence of packet loss), there's
going to be just two challenge/reply exchanges (one in each direction) for
every neighbour acquisition.  This implies that there is no opportunity
to establish RTT state, and no useful opportunity to reset timers when
a reply is received.

-- Juliusz