6500, why can I ping and telnet to a subnet address?

[danielbarri]

I have configured one of the vlans in a MSFC-2 with a 29 bits subnet mask length(e.g. xx.xx.xx.8/29). I was surprised when, to a ping scan, the subnet address responded, and I could telnet also to this address.

That is not the case when the mask length is 23 or 24.

[t.baranski]

I've never seen a Cisco device *not* do this, regardless of subnet mask length. I believe an early RFC either required or recommended that implementations respond to traffic destined to these addresses. But this is generally undesirable these days, so blocking traffic to subnet/broadcast addresses with ACL's is a good idea.