[clamav-users] A workaround for the major ClamAV DB update delays we have been experiencing

Paul Kosinski clamav-users at iment.com
Sat Dec 8 10:37:15 EST 2018


Not sure what DNS caching would have to do with this. As I understand
"anycast", it happens at the IP address level. An anycast IP address
gets routed differently depending are where you are -- different
(regional) routers have different "next hops" for the IP address, and
it eventually ends up at a "nearby" server. This is in addition to the
fact that database.clamav.net resolves to 5 different IP addresses (all
of which are anycast IPs, I would guess).

The Cloudflare servers, although they have the same IP address(es) seem
to identify themselves by means of an HTTP header that they return:

  CF-RAY: 4852e02c35ae5a5c-BOS
  CF-RAY: 48526af5624356c3-IAD

Finally, AFAIK, I always get the same result for 

  "dig TXT current.cvd.clamav.net"

no matter where I 'dig' (or 'host') from.



On Fri, 7 Dec 2018 19:27:20 -0500
Eric Tykwinski <eric-list at truenet.com> wrote:

> This is getting rather technical, and probably some of CloudFlare’s
> secret sauce. It sounds like the anycast DNS that cloudflare hosts
> isn’t really working, or at least I would assume that they are using
> anycast.
> 
> So you query current.cvd.clamav.net <http://current.cvd.clamav.net/>
> but are getting different results at IAD and BOS.  Now next is the
> inclusion of Comcast, which may and probably is caching DNS records
> beyond normal TTLs which could cause the difference.  I personally
> always run an Unbound cache server on my mailserver networks to cache
> dns for at least an hour for rbls that I’m not rsyncing, but that
> could cause an issue with Microsoft’s wonderful 10 second MX
> records.  So that’s where I’ve run into this issue, but not often
> enough since I’m just caching for an hour and probably MS expects it.
> 
> So my guess, is probably not anycast, but a caching DNS server that
> is still giving older records.
> 
> Sincerely,
> 
> Eric Tykwinski
> TrueNet, Inc.
> P: 610-429-8300
> 
> > On Dec 7, 2018, at 6:20 PM, Paul Kosinski <clamav-users at iment.com>
> > wrote:
> > 
> > As some of you may be aware, ever since ClamAV began using
> > Cloudflare, we have seen many occasions when files like daily.cvd
> > were not available to our LAN until well after the DNS TXT record
> > implied they should be.
> > 
> > However, we discovered that these same files *are* available to our
> > Web/email server right away. So what is the difference? The first
> > difference is that our Web server (a VM) is offsite, and is served
> > by the "IAD" Cloudflare complex, whereas our local setup is served
> > by the "BOS" Cloudflare complex.
> > 
> > The second, and likely explanatory difference, is that our local
> > setup is connected via Comcast (a dynamic IP and all that), while
> > our Web server (with its static IP etc.) is almost certainly more
> > directly connected to the Internet as a whole.
> > 
> > The workaround we have adopted is as follows: we installed a
> > "tinyproxy" server on our offsite VM. To ensure it only proxys for
> > us, it listens on the encrypted OpenVPN tunnel we already had in
> > place for FTP uploads etc. Then, instead of directly accessing
> > database.clamav.net, freshclam uses our remote VM as a proxy,so
> > that the cvd files are downloaded indirectly from Cloudflare's IAD
> > server complex (via tinyproxy) rather than directly from
> > Cloudflare's BOS server complex.
> > 
> > Since switching to this workaround a few days ago, we haven't
> > observed any delays: the cvd files are available right away when
> > the DNS TXT query says they should be.
> > 
> > I strongly suspect that Comcast is the culprit in the delays that
> > had plagued us. This is especially suggested by the fact that
> > Cloudflare returns a "Cache-Control:" header similar to:
> > 
> >  Cache-Control: public, max-age=13672
> > 
> > where the max-age value varies, but is often several hours.
> > 
> > In my opinion, for data like ClamAV virus updates, the
> > "Cache-Control:" should specify "no-cache". Can Cloudflare do this
> > for ClamAV?
> > 
> > ---------------------------------------------------------------------
> > 
> > Below is a pair of recent (pre-workaround) log excerpts. They show a
> > delay of over 2.5 hours experienced from BOS (via Comcast) vs no
> > delay from IAD.
> > 
> > Note that the BOS "Date:" timestamp of 16:49:01 GMT *still* shows
> > a "Last-Modified:" timestamp of 06:15:18 GMT, while IAD already
> > shows the up-to-date "Last-Modified:" timestamp of 14:14:30 GMT at
> > the much earlier "Date:" of 14:29:01 GMT!
> > 
> > 
> >  IAD
> > 
> >    Date: Sun, 02 Dec 2018 14:09:01 GMT
> >    Last-Modified: Sun, 02 Dec 2018 06:15:18 GMT
> >    ClamAV-VDB:02 Dec 2018 01-14
> > -0500:25172:2167574:63:13c670e3a525c4fd17bf65524ff05fcd:nwPmlNwUbKmexgT
> > 
> >    Date: Sun, 02 Dec 2018 14:29:01 GMT
> >    Last-Modified: Sun, 02 Dec 2018 14:14:30 GMT
> >    ClamAV-VDB:02 Dec 2018 09-13
> > -0500:25173:2167842:63:ba557f61737b9d4b66acc96f7044b524:3nBAOxo97ssSNZb
> > 
> > 
> >  BOS
> > 
> >    Date: Sun, 02 Dec 2018 14:09:01 GMT
> >    Last-Modified: Sun, 02 Dec 2018 06:15:18 GMT
> >    ClamAV-VDB:02 Dec 2018 01-14
> > -0500:25172:2167574:63:13c670e3a525c4fd17bf65524ff05fcd:nwPmlNwUbKmexgT
> > 
> >    Date: Sun, 02 Dec 2018 14:29:01 GMT
> >    Last-Modified: Sun, 02 Dec 2018 06:15:18 GMT
> >    ClamAV-VDB:02 Dec 2018 01-14
> > -0500:25172:2167574:63:13c670e3a525c4fd17bf65524ff05fcd:nwPmlNwUbKmexgT
> > 
> >    Date: Sun, 02 Dec 2018 14:49:01 GMT
> >    Last-Modified: Sun, 02 Dec 2018 06:15:18 GMT
> >    ClamAV-VDB:02 Dec 2018 01-14
> > -0500:25172:2167574:63:13c670e3a525c4fd17bf65524ff05fcd:nwPmlNwUbKmexgT
> > 
> >    Date: Sun, 02 Dec 2018 15:09:01 GMT
> >    Last-Modified: Sun, 02 Dec 2018 06:15:18 GMT
> >    ClamAV-VDB:02 Dec 2018 01-14
> > -0500:25172:2167574:63:13c670e3a525c4fd17bf65524ff05fcd:nwPmlNwUbKmexgT
> > 
> >    Date: Sun, 02 Dec 2018 15:29:02 GMT
> >    Last-Modified: Sun, 02 Dec 2018 06:15:18 GMT
> >    ClamAV-VDB:02 Dec 2018 01-14
> > -0500:25172:2167574:63:13c670e3a525c4fd17bf65524ff05fcd:nwPmlNwUbKmexgT
> > 
> >    Date: Sun, 02 Dec 2018 15:49:02 GMT
> >    Last-Modified: Sun, 02 Dec 2018 06:15:18 GMT
> >    ClamAV-VDB:02 Dec 2018 01-14
> > -0500:25172:2167574:63:13c670e3a525c4fd17bf65524ff05fcd:nwPmlNwUbKmexgT
> > 
> >    Date: Sun, 02 Dec 2018 16:09:01 GMT
> >    Last-Modified: Sun, 02 Dec 2018 06:15:18 GMT
> >    ClamAV-VDB:02 Dec 2018 01-14
> > -0500:25172:2167574:63:13c670e3a525c4fd17bf65524ff05fcd:nwPmlNwUbKmexgT
> > 
> >    Date: Sun, 02 Dec 2018 16:29:01 GMT
> >    Last-Modified: Sun, 02 Dec 2018 06:15:18 GMT
> >    ClamAV-VDB:02 Dec 2018 01-14
> > -0500:25172:2167574:63:13c670e3a525c4fd17bf65524ff05fcd:nwPmlNwUbKmexgT
> > 
> >    Date: Sun, 02 Dec 2018 16:49:01 GMT
> >    Last-Modified: Sun, 02 Dec 2018 06:15:18 GMT
> >    ClamAV-VDB:02 Dec 2018 01-14
> > -0500:25172:2167574:63:13c670e3a525c4fd17bf65524ff05fcd:nwPmlNwUbKmexgT
> > 
> >    Date: Sun, 02 Dec 2018 17:09:01 GMT
> >    Last-Modified: Sun, 02 Dec 2018 14:14:30 GMT
> >    ClamAV-VDB:02 Dec 2018 09-13
> > -0500:25173:2167842:63:ba557f61737b9d4b66acc96f7044b524:3nBAOxo97ssSNZb




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