In trying to diagnose a failover problem with my Cisco ASA 5520 firewalls, I ran a traceroute to www.btfl.com and, much to my surprise, some of the hops came back as RFC 1918 addresses. Just to be clear, this host is not behind my firewall and there is no VPN involved. I have to connect … Read more
IETF RFC 7505 describes MX records for a domain/host that explicitly should not receive email. This is accomplished by pointing the MX at the Domain Name System root. For example, nomail.example.com. 86400 IN MX 0 “.” Why is this needed? In my understanding, explicit refutation is available by using domains under the TLD invalid. For … Read more
A third-party email gateway relay is refusing to process a message for an email address we’re sending to. The address is in the format of firstname..lastname@recipientdomain.com (note the two periods). Is this allowed by RFC guidelines? RFC 2822 seems to object to this in section 3.4.1: The locally interpreted string is either a quoted-string or … Read more
Is there ever a legitimate reason for the SMTP “MAIL FROM:” field to not match the “From:” field in the DATA section of a message, besides mailing lists? From https://stackoverflow.com/questions/1750194/smtp-why-does-email-needs-envelope-and-what-does-the-envelope-mean: “But, to continue your snail mail metaphor, most professional letters will contain the sender’s and recipient’s addresses printed on the letter itself. Those addresses are … Read more
Before anyone asks: I’ve seen When do DNS queries use TCP instead of UDP? and it doesn’t answer my question. All I keep hearing is “if the answer is too long, DNS will use TCP“. This does not explain how it happens though. So here’s the situation: DNS client asks for resolution of a record … Read more
It’s extremely common for RFCs to be cited in support of opinions (including Serverfault Q&A’s), but the average IT employee has a very poor understanding in regards to which RFCs define standards and which ones are purely informative. This should be no surprise: system administrators of all experience levels typically avoid glazing their eyes at … Read more
We are trying to move all our websites we host to CNAMES as we are planning on moving servers in the new year and would like the ability to move some clients to one server and other clients somewhere else. We were planning on giving clients a unique CNAME which we can then change at … Read more
And is it configurable? Can I set up Tomcat so that a URL with, say, 200K of query params goes through successfully to the contained servlet? Yes, I know one should use POST when you have lots of data; that’s a less pleasant option in this particular case. The contained application (a search engine) expects … Read more
