Firewall Wizards mailing list archives
Re: ICMP Packets.
From: Bennett Todd <bet () rahul net>
Date: Thu, 4 Jun 1998 10:48:57 -0700
1998-06-04-07:11:54 Matthew Green:
[I] was surprised at the number of people advocating the "block all icmp packets" approach.
I haven't seen too many such. Rather, the original poster who started this thread asked _what_ sort of ICMP packets (like the ``need frag'' you refer to for path MTU discovery) we should let through because they're actually necessary. Even Perry has slipped as far as to concede that it might be appropriate to block some ICMP types. What those of us of the ``old school'' are hoping is that someone will give us a list of the ICMP packet types that _are_ needed, along with why --- some of us are keen fans of the ``block everything except that which is explicitly permitted'' style of firewall config.
if you really care about security such that you think blocking ICMP messages is a good thing, _why_ don't you also block normal IP packets as well?
I do, indeed --- I block all IP packets except a very select few that I explictly choose to let in. Likewise UDP. I'd be inclined to expect that the same approach would be appropriate for ICMP, no? So, while I've not yet looked at the RFC to translate the gist into actual packet types suitable for plugging into a filter, I have gotten a gist --- I came into this knowing about the need for the fragmentation packet for path MTU discovery, and Perry just taught me that I'll need to let some more through so people getting SYN-ed with spoofed source can get an ``nope, ain't me'' back from my server. We're getting there.... -Bennett
Current thread:
- Re: ICMP Packets., (continued)
- Re: ICMP Packets. James R Grinter (Jun 02)
- Re: ICMP Packets. Henry Hertz Hobbit (Jun 03)
- Re: ICMP Packets. Don Kendrick (Jun 02)
- Re: ICMP Packets. Perry E. Metzger (Jun 02)
- Re: ICMP Packets. Perry E. Metzger (Jun 03)
- Re: ICMP Packets. Bennett Todd (Jun 04)
- Re: ICMP Packets. Paul D. Robertson (Jun 05)
- Re: ICMP Packets. Don Kendrick (Jun 02)
- Re: ICMP Packets. Perry E. Metzger (Jun 03)
- Re: ICMP Packets. matthew green (Jun 04)
- Re: ICMP Packets. Bennett Todd (Jun 04)
- Re: ICMP Packets. Darren Reed (Jun 05)
- Re: ICMP Packets. tqbf (Jun 07)
- Re: ICMP Packets. Darren Reed (Jun 07)
- Re: ICMP Packets. blast (Jun 08)
- Re: ICMP Packets. Aleph One (Jun 09)
- Re: ICMP Packets. Perry E. Metzger (Jun 03)
- Re: ICMP Packets. James R Grinter (Jun 02)
- Re: ICMP Packets. Ge' Weijers (Jun 05)
- Re: ICMP Packets. Bennett Todd (Jun 05)
- Re: ICMP Packets. tqbf (Jun 04)
- Re: ICMP Packets. Paul D. Robertson (Jun 05)