# ll $(which nslookup) lrwxrwxrwx 1 root root 17 Mar 21 13:16 /usr/bin/nslookup -> ../../bin/busybox I'm not sure it's the old nslookup that we're thinking of... -- David P. On Mon, Mar 24, 2014 at 5:58 PM, Dave Taht wrote: > I ship dig as an optional package for cerowrt. > > I think it's in bind-tools or bind-utils. It is terribly big, but most > people hae enough spare flash to have it. > > An > > opkg update > opkg list | less > > will show you what is available. > > I will argue that nobody wants to add functionality to the primitive > nsupdate.... > > On Mon, Mar 24, 2014 at 1:27 PM, David Personette > wrote: > > Phil, > > > > With the exception of the extra dependencies (dig and python), I like > this. > > I would suggest that if DNSSEC will be enabled, that nslookup (I think > > that's the only command line resolver included by CeroWRT/OpenWRT base > > installs) be extended to have a similar option as dig, to resolve without > > DNSSEC. > > > > The only other issue I see is if the router is brought online before > > internet access is available. If I read your code correctly, it will try > 4 > > times per defined server (with and without DNSSEC for IPv4 and IPv6), > then > > exit. It either needs to keep trying until it succeeds, or be called > every > > time a connection comes up (shutting down NTPd prior and restarting > after). > > > > Thanks. > > > > -- > > David P. > > > > > > > > On Mon, Mar 24, 2014 at 3:12 PM, Phil Pennock > > wrote: > >> > >> On 2014-03-21 at 23:33 -0400, Joseph Swick wrote: > >> > I've been lurking for several months now on the list and I remember > some > >> > discussion about trying to find acceptable methods for bootstrapping > the > >> > local system time so that DNSSEC would work. > >> > >> I raised this on the ntp-pool mailing-lists last year, looking for a > >> solution because of the chicken/egg bootstrap, with suggested approaches > >> and some trial scripts. Eg: > >> > >> http://lists.ntp.org/pipermail/pool/2013-July/006569.html > >> > >> For context, I'm currently running OpenWRT; attached is the > >> /etc/init.d/ntpdate which I'm using. It relies upon having Python and > >> dig installed, as I haven't gotten around to building a small C utility > >> to do just this task, but perhaps the approach is useful enough that > >> someone else might do so? > >> > >> In summary: if the current time is less than the timestamp on the > >> unbound-maintained copy of the root zone trust anchors, then bump the > >> time up at least that far, because we must be at >= that timestamp, and > >> this increases the odds that DNSSEC will validate if we haven't been > >> off-line for too long. > >> > >> Then, for each hostname in the $STEP_SERVERS list (which could be > >> taken from ntp.conf or uci config or whatever, but here is just > >> hardcoded), I try to resolve IPv4 then IPv6, first with DNSSEC left > >> enabled, and then with DNSSEC disabled via `dig +cd`. The first dig > >> command to return results is the one which is used. > >> > >> The idea is to minimize the potential vulnerability of syncing to a bad > >> timesource, by using DNSSEC if it's available and works, after making > >> sure it has a reasonable chance of working if we've just rebooted, and > >> only if we've been off-line for some time do we fall back to insecure > >> DNS. > >> > >> Make sure that the START value is appropriate for your systems; I've > >> found the OpenWRT defaults to be sufficiently broken that I stomp on > >> them on reinstall. I run ntpdate once the network and firewall are up, > >> but just before ntpd and both of those well before other network > >> services which might depend upon time. > >> > >> Regards, > >> -Phil > >> > >> #!/bin/sh /etc/rc.common > >> # Copyright (C) 2006-2008 OpenWrt.org > >> # Copyright (C) 2013 Phil Pennock > >> > >> START=60 > >> > >> STEP_SERVERS="0.openwrt.pool.ntp.org 1.openwrt.pool.ntp.org > >> 2.openwrt.pool.ntp.org" > >> TIMEOUT="2" # in seconds > >> PRESEED_TIMESTAMP_FN="/etc/unbound/runtime/root.autokey" > >> > >> # The core problem is that with DNSSEC, an invalid time prevents > >> resolution > >> # of DNS, but we need DNS to be able to find time-servers to get a good > >> time > >> # to be able to resolve DNS. > >> # > >> # We break out of this "Catch 22" situation by _trying_ normal DNS > >> resolution, > >> # IPv4 and then IPv6, and only if those fail do we forcibly disable > DNSSEC > >> # by using dig(1)'s +cd flag ("checking disabled"); trying normally > first > >> # protects us against malicious DNS trying to point us to bad > >> time-servers, > >> # if we've enough state that we _should_ already be protected. > >> # > >> # The "insecure" approach we regress to, as a last resort, is the same > way > >> # the Internet functioned for decades. There is a DoS+hijack attack > path > >> # here, but if we don't have a good battery-backed clock to protect us, > we > >> # don't have a better solution. > >> > >> # Also, per a suggestion from Doug Calvert, we can use the timestamp of > >> # modification of the unbound root.key file itself as an approximate > time. > >> # Unbound updates the file on every refresh, so it's not too far off. > >> > >> preseed_approximate_time() { > >> # Unfortunately, date(1) on OpenWRT can't parse the timestamp > >> # output from ls. > >> python -c ' > >> import os, time, sys > >> fn=sys.argv[1] > >> min_time=os.stat(fn).st_ctime > >> if time.time() < min_time: > >> want=time.strftime("%Y%m%d%H%M.%S", time.gmtime(min_time)) > >> os.system("date -u -s %s" % want)' "$PRESEED_TIMESTAMP_FN" > /dev/null > >> } > >> > >> resolve_hostname_v4() { > >> # we use the grep both to filter out cname referrals and to detect empty > >> # results > >> local hn="$1" > >> shift > >> dig +nodnssec +short "$@" -t a "$hn" | grep '^[0-9][0-9.]*$' > >> } > >> > >> resolve_hostname_v6() { > >> local hn="$1" > >> shift > >> dig +nodnssec +short "$@" -t aaaa "$hn" | grep -i > >> '^[0-9a-f][0-9a-f.:]*$' > >> } > >> > >> resolve_one_server() { > >> local hn="$1" > >> resolve_hostname_v4 $hn && return > >> resolve_hostname_v6 $hn && return > >> resolve_hostname_v4 $hn +cd && return > >> resolve_hostname_v6 $hn +cd && return > >> } > >> > >> resolve_step_servers() { > >> local server ips > >> for server in $STEP_SERVERS ; do > >> resolve_one_server $server > >> done > >> } > >> > >> start() { > >> preseed_approximate_time > >> for s in $(resolve_step_servers) ; do > >> /usr/sbin/ntpdate -s -b -u -t "$TIMEOUT" "$s" && break > >> done > >> > >> } > >> > >> _______________________________________________ > >> Cerowrt-devel mailing list > >> Cerowrt-devel@lists.bufferbloat.net > >> https://lists.bufferbloat.net/listinfo/cerowrt-devel > >> > > > > > > _______________________________________________ > > Cerowrt-devel mailing list > > Cerowrt-devel@lists.bufferbloat.net > > https://lists.bufferbloat.net/listinfo/cerowrt-devel > > > > > > -- > Dave Täht > > Fixing bufferbloat with cerowrt: > http://www.teklibre.com/cerowrt/subscribe.html >