On Monday 18 June 2012 23:54:50 Stephen Hemminger wrote: > > First off, STP is not a secure protocol. It assumes a trust in any bridge > it excepts PDU's from. That is why Cisco as bpdu guard to ignore stuff > from rogue endpoints. In Linux, you can do the same with netfilter but > most users dont. > > Second, the standard (Linux is based on old 1998 version) allows any > value for forwarding delay (0 .. 255 seconds). The encoding of timer > value section implies that. > Hello, Stephen! Standards (both -1998 and -2004 revisions) do say nothing about validation of timers (except one issue) and you gave a good point that encoding clearly allows any timer value from 0.0 s to 255+255/256 s. Now, to the exceptional issue: 9.3.3 a) of -1998 (9.3.4 a) of -2004) =============================================== a) The BPDU Type denotes a Configuration BPDU and the BPDU contains at least 35 octets, and the value of the BPDUs Message Age parameter is less than that of its Max Age parameter ... [skip] =============================================== So, the standard clearly requires the BPDU where MessageAge < MaxAge to be dropped. Don't you think that including this check in Linux bridging code is worthwhile? -- With Best Regards, Vitalii Demianets
