[Dnsmasq-discuss] DNSMasq and CDN (akamai, etc)

Simon Kelley simon at thekelleys.org.uk
Fri Jul 8 11:28:06 BST 2011


I don't know if this

http://tools.ietf.org/id/draft-vandergaast-edns-client-ip-01.txt

is going anywhere (the latest draft has expired) but if it does then
support in dnsmasq may be in order.




Ed W wrote:
> I have a curious problem being served sub-optimal CDN servers when using
> opendns or googledns
> 
> I am in London/UK and opendns appears not to have a local DNS cache, so
> attempting to access bbc.co.uk and view the page images gives these results:
> 
> # dig news.bbcimg.co.uk
> 
> ; <<>> DiG 9.7.3 <<>> news.bbcimg.co.uk
> ;; global options: +cmd
> ;; Got answer:
> ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 57231
> ;; flags: qr rd ra; QUERY: 1, ANSWER: 5, AUTHORITY: 0, ADDITIONAL: 0
> 
> ;; QUESTION SECTION:
> ;news.bbcimg.co.uk.		IN	A
> 
> ;; ANSWER SECTION:
> news.bbcimg.co.uk.	2413	IN	CNAME	newsimg.bbc.net.uk.
> newsimg.bbc.net.uk.	202	IN	CNAME	news.bbc.co.uk.edgesuite.net.
> news.bbc.co.uk.edgesuite.net. 3427 IN	CNAME	a1733.g.akamai.net.
> a1733.g.akamai.net.	10	IN	A	216.246.75.138
> a1733.g.akamai.net.	10	IN	A	216.246.75.113
> 
> ;; Query time: 84 msec
> ;; SERVER: 192.168.105.212#53(192.168.105.212)
> ;; WHEN: Fri Jul  8 10:22:02 2011
> ;; MSG SIZE  rcvd: 168
> 
> That ip range is in the USA and about 85ms away from me.
> 
> 
> Instead using google dns I get:
> 
> # dig news.bbcimg.co.uk @8.8.4.4
> ..
> a1733.g.akamai.net.	19	IN	A	193.28.236.135
> a1733.g.akamai.net.	19	IN	A	193.28.236.136
> 
> These are 41ms away
> 
> 
> If I switch to my ISP DNS servers:
> 
> # dig news.bbcimg.co.uk @212.69.36.3
> ..
> a1733.g.akamai.net.	15	IN	A	92.123.154.18
> a1733.g.akamai.net.	15	IN	A	92.123.154.33
> 
> These are 15ms away
> 
> 
> So having discovered that using nominally faster DNS servers has amongst
> other things the disadvantage that CDNs might pass you to suboptimal
> choices, hurting you multiple times per web page...
> 
> So I tried this configuration:
> 
> server=8.8.4.4
> server=/akamai.net/212.69.36.3
> server=/edgesuite.net/212.69.36.3
> 
> But I notice that since the reply comes back in a single response that
> the CNAMES are not resolved using the alternative server parts.

Yes, that approach is not tenable.
> 
> Disregarding all the privacy debates about using these super DNS
> servers, does anyone have any thoughts on how to better handle getting
> redirected to a local CDN, other than perhaps using only the ISP servers?


I wonder if your ISP has a cache for the BBC content withing its
network? Traffci from bbc.co.uk must make up a huge proportion of
external traffic for UK ISPs.

Maybe try it the other way around, (ie use openDNS or Google DNS for
everything _except_ (list of big site likely to use local CDNs)

Simon.


> 
> Thanks
> 
> Ed W
> 
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