[Unbound-users] Queries and responses "serialized" when using forwarder
ondrej.mikle at nic.cz
Fri Feb 10 14:43:23 UTC 2012
I've noticed that when I set forwarder in unbound or libunbound (via
forward-zone or ub_ctx_resolvconf, respectively), the resolution seems
to be always serialized, no matter what settings of *-slabs, threads or
target-fetch-policy is (i.e. "nicely" alternating query-response).
Without forwarder, requests seem to be parallelized, at least to some
I couldn't find any explanation for this behavior in documentation, RFCs
For example, resolving A record of addons.mozilla.org using forwarder
looks like (latest unbound 1.4.16, empty cache):
No. Time Info
5 0.731801 Standard query A addons.mozilla.org
6 0.921957 Standard query response A 126.96.36.199 RRSIG
7 0.922192 Standard query DNSKEY <Root>
8 0.922689 Standard query response DNSKEY DNSKEY RRSIG
9 0.923067 Standard query DS org
10 0.956492 Standard query response DS DS RRSIG
11 0.957263 Standard query DNSKEY org
12 0.957761 Standard query response DNSKEY DNSKEY DNSKEY DNSKEY RRSIG
13 0.957945 Standard query DS mozilla.org
14 0.958194 Standard query response DS RRSIG
15 0.958298 Standard query DNSKEY mozilla.org
16 1.045979 Standard query response DNSKEY DNSKEY DNSKEY RRSIG RRSIG
For example, after retrieving response for "IN A addons.mozilla.org" we
know which zone to ask for DS and DNSKEY and could ask for DS and DNSKEY
for root, org and mozilla.org in parallel. Would that be against some
RFC, best practices or it's just not implemented for some other reason
(like me overlooking a reason why it wouldn't work in a general case)?
Why I am asking: on a slow line (e.g. mobile phone, Tor) the number of
necessary round-trips makes quite a difference.
Suppose I'd want to work around this by hacking libunbound a bit -
client sends "IN A addons.mozilla.org" and receives all the necessary
packets for validation in the usual DNS format as if client's cache was
empty (DS a DNSKEY for root, org, mozilla.org).
One obvious issue is size: with a CDN that chains via CNAME/DNAME
through multiple zones, the response can be rather big.
Size aside, is there other issue that can make the implementation
difficult to do correctly? I've seen Adam Langley's DNSSEC-stapling
draft, but that's more complex since it tries to adress more issues at once.
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