Questions tagged [rfc]

A Request for Comments (RFC) is a publication of the Internet Engineering Task Force (IETF) and the Internet Society, the principal technical development and standards-setting bodies for the Internet.

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DHCP renewal can't go through because DHCP server is down

To my experience, if a DHCP client tries to renew its lease, but the DHCP server is down, and after the lease time is over, there are two possible scenarios: The client keeps the IP The client goes ...
1 vote
1 answer
287 views

is "GET /" a valid HTTP request?

I noticed that sending GET / (+CRLF) to some webservers (e.g. from a well-known search provider) results in a HTTP/1.0 200 OK message. Other webserver respond with a HTTP/1.0 400 error. To my ...
1 vote
1 answer
212 views

Is it legal for a DHCP relay agent to relay RENEWAL requests that were directly unicast to the "Server identifier" server?

I'm observing the following in a packet capture. Client -> Broadcast : DHCP Request Relay -> Client : DHCP Ack (Option 54 == Server) ... After T1 expires ... Client -> Server Identifier ...
46 votes
6 answers
57k views

DNS using CNAMEs breaks MX records?

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 ...
0 votes
1 answer
15k views

Yahoo Mail: "No mx record found for domain"

Yahoo's Mail servers are refusing to deliver messages to the mail server for a domain I manage. It complains that there is no MX record for the domain. According to my understanding for many years, ...
23 votes
2 answers
34k views

Are two periods allowed in the local-part of an email address?

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 [email protected] (note the two periods)...
3 votes
1 answer
5k views

Which characters/values are allowed to use in DNS?

While I was looking on RFCs of DNS because of implementation to check underscore in CNAME records, I found this interesting discussion and RFC with interesting point: https://www.ietf.org/mail-...
43 votes
1 answer
16k views

How does the DNS protocol switch from UDP to TCP?

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 ...
1 vote
0 answers
105 views

RFC 3074 DHCP Load Balancing STID vs RFC 2131 DHCP xid

Section 2.2 of RFC 3074 defines a Service Transaction ID (STID) as: An attribute of the individual client requests used for load-balancing. However, section 2 of RFC 2131 defines the xid field of a ...
2 votes
1 answer
2k views

How to block this range of RFC1918 on Ubuntu server?

We're running an IKEv2 VPN on a Ubuntu server. One of our users has run a NetScan while using our VPN, which has upset the server provider. This is what the server provider has recommended: We would ...
7 votes
1 answer
2k views

Which ICMP types (v4/v6) should not be blocked?

I have made a lot of research into this and have found that some references contradict each other. IPV6 For example RFC4890 says the following types should be allowed for optimal functionality: Type ...
0 votes
1 answer
4k views

syslog-ng: how to configure sending RFC5424 messages with octet-counting framing

Please don't bother reading this question. syslog-ng is already set up to send RFC5424 messages with octet-counting framing by default. I was confused by the behaviour of another component. This ...
0 votes
2 answers
89 views

Doubts about DKIM verification (RFC6376)

Good morning, https://www.rfc-editor.org/rfc/rfc6376#section-5 reads: "Survivability of signatures after transit is not guaranteed, and signatures can fail to verify through no fault of the ...
3 votes
0 answers
108 views

Why not shorten a single :0000: field in IPv6

rfc5952, section 4.2.2 "Handling One 16-Bit 0 Field" goes: The symbol "::" must not be used to shorten just one 16-bit 0 field. For example, the representation 2001:db8:0:1:1:1:1:...
3 votes
2 answers
2k views

How can DHCPv6 server allocate fixed IPv6 addresses to clients if it's not allowed to interpret DUID?

According to RFC3315: Each DHCP client and server has a DUID. DHCP servers use DUIDs to identify clients for the selection of configuration parameters and in the association of IAs with clients. DHCP ...
11 votes
3 answers
22k views

Does the presence of a Content-ID header in an email MIME mean that the attachment must be embedded?

Two different third-party email products we have are reacting differently to the presence of a content-id header in the MIME source of an email. This is resulting in an inconsistent user experience ...
-1 votes
2 answers
350 views

Do glue records/child hosts override DNS wildcard entries or A records at the domain names DNS servers records?

Do glue records/child hosts override DNS wildcard entries or A records at the domain names DNS servers records? example: ns1.example.com = 1.1.1.1 at registrar DNS glue /child host ns1.example.com = 2....
0 votes
1 answer
70 views

Two way handshake for WHOIS protocol? RFC 3912

From RFC 3912: 3. Protocol Example If one places a request of the WHOIS server located at whois.nic.mil for information about "Smith", the packets on the wire will look like: client ...
2 votes
2 answers
4k views

Creating a RFC 1123 compliant date for HTTP header creation on the CLI

I'm trying to create a HTTP 1/1 compliant date header using standard unix date(1) in order to post this to a RESTful server using curl or similar. Any ideas what format to pass to date(1) to get this ...
19 votes
2 answers
4k views

Why is RFC 7505 (Null MX) necessary?

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. ...
49 votes
4 answers
119k views

What's the maximum URL length in Tomcat?

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 ...
2 votes
1 answer
2k views

LDAPS Microsoft Active Directory Multiple Certificates RFC6125

We have an Microsoft Active Directory Domain with a large pool of domain controllers (DC) that are are setup with LDAP. These are all setup with LDAPS and uses Certificate Services via a template to ...
1 vote
1 answer
3k views

IPv6 address text notation with prefix: inside or outside square brackets?

I'm skimming through some IPv6 related RFCs. Some claim that a prefix should be written outside of the square brackets, whereas others have it tacked on to the address directly. Specifically, RFC4291, ...
0 votes
1 answer
751 views

Email format RFCs

I know there are lots of RFCs that changed how an email can be made. However, most of the RFCs don't apply to for example outlook. First of all, what are RFCs exactly? And why don't for example ...
0 votes
1 answer
379 views

DHCPv6 (RFC 8415) - What are reasonable initial values for time intervals T1/T2?

As described in Section 18.2. - Client Behavior of DHCP - RFC 8415 a client uses the Solicit message to discover DHCP servers configured to assign leases or return other configuration parameters on ...
1 vote
1 answer
3k views

Master ipv4 CIDR configuration for private cluster in GCP

I'm trying to create a private cluster in GCP as per the steps mentioned here: https://cloud.google.com/kubernetes-engine/docs/how-to/private-clusters As per this, the ipv4 address for the master ...
0 votes
1 answer
85 views

Where to find symbol definitions for RFC protocol flow diagram?

I am reading RFC5077, and bumped into following diagram: ClientHello (empty SessionTicket extension)--------> ServerHello ...
0 votes
1 answer
339 views

RFC 5321 requires my SMTP server with the Enhanced-Status-Codes service extension to reply with “250 OK”

RFC 2034 4. The Enhanced-Status-Codes service extension Servers supporting the Enhanced-Status-Codes extension must preface the text part of almost all response lines with a status code. As in ...
7 votes
2 answers
14k views

Why isn't net.ipv4.tcp_rfc1337 enabled by default?

The tcp_rfc1337 setting seems to have a solution for TIME-WAIT Assassination. The first problem is that old duplicate data may be accepted erroneously in new connections, leading to the sent data ...
3 votes
1 answer
3k views

How is truncation performed in DNS according to RFC 1035?

I'm trying to implement my own DNS server from scratch. However, I'm having difficulty understanding how RFC 1035 recommends truncation to be performed. Section 6.2 says: When a response is so long ...
2 votes
3 answers
1k views

Message-ID of delivery report is equal to original mail

I discoverd that the delivery status report has the same message-id as the original mail. Here is the text of the delivery report: Incoming DSN message: From: Mail Delivery Subsystem <postmaster@...
30 votes
4 answers
73k views

Legitimate reasons SMTP “MAIL FROM:” will not match “From:” Header in DATA

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/...
0 votes
1 answer
148 views

rfc3207 smtp starttls restriction confusion

From https://www.rfc-editor.org/rfc/rfc3207: A publicly-referenced SMTP server MUST NOT require use of the STARTTLS extension in order to deliver mail locally. This rule (1.) prevents the STARTTLS ...
-3 votes
1 answer
400 views

Same Interface routing with ICMP-Redirect disabled? [closed]

I don't want to talk around the bush for long. I disagree with a friend how a router would behave in a special configuration. Unfortunately I can't test it here to check my point of view. Specifically,...
11 votes
2 answers
3k views

RFC that requires DNS servers to respond to unknown domain requests

My domain registrar and DNS provide currently ignores DNS requests to unknown domains. By ignore I mean black-holes and never responds which causes my DNS clients and resolver libraries to retry, ...
4 votes
1 answer
97 views

Should I reject mail to test domains?

RFC6761 states about example domains (such as example.com): Application software SHOULD NOT recognize example names as special and SHOULD use example names as they would other domain names. ...
3 votes
1 answer
658 views

TLS Implementation/RFC interpretation

Does the Server Hello break the RFC? There seems to be contradiction in RFC. A customer claims our device (Citrix Netscaler) returns Extension (ec_point_formats: EC point format: uncompressed) when ...
0 votes
1 answer
1k views

Is it possible DNS packet contains more than one SOA resource record

I've read RFC 1034 and RFC 1035 to learn about DNS protocol standards. I'm searching to find a limit occurring of SOA resource records. I'm aware that A, AAAA, CNAME, NS, MX, TXT RRs have no limit. ...
1 vote
0 answers
195 views

Is there any IETF / RFC standard defined for hosts file encoding?

While going through the accepted answer for hosts file ignored, how to troubleshoot?, I observed the statement "The hosts file should encoded in ANSI or UTF-8 without BOM". As I personally faced ...
1 vote
1 answer
284 views

Which side of this SMTP conversation is correct?

I have an odd scenario with two mail servers communicating with one another and need help determining which one is behaving correctly. It's a little complicated to explain, so I think a SMTP ...
4 votes
3 answers
6k views

Does the OS X DHCP client support classless static routes (RFC3442)?

Simply put: does Mac OS X support RFC3442? RFC3442 implements DHCP codes (121 and 249) to provide classless static routes to DHCP clients. I can only seem to find rather old information circa 2005-...
-1 votes
1 answer
672 views

Can a non-authoritative name server give any response it likes to?

Our domain registrar allows us to either make use of our own DNS servers or to use theirs (configuring DNS entries in their web interface); I suppose this is a common situation. We have opted to set ...
1 vote
2 answers
7k views

Space a valid delimiter for email addresses in email header?

Is it syntactically correct to delimit multiple email recipients in the "To" header of an email with spaces only or do I need to use another delimiter (a semicolon or the like)? Example (MIME data ...
44 votes
2 answers
3k views

Which RFCs should be cited as internet standards?

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 ...
0 votes
1 answer
1k views

Special characters in mail (address) headers and RFC2047 encoding

I have some unexpected handling of RFC2047 "From" headers on Exim. (Actual addresses have been changed, the original display name contained non-ASCII characters) For this "From" ...
1 vote
1 answer
212 views

Why IPs from the Private Address Space would be reachable through public network, and what customers can do about it?

Scenario: I have a customer running a Win7 Pro and an OpenVPN client; this workstation is used from one of their employees to send remote cmds to the (Windows) OpenVPN server, both using psexec and ...
2 votes
1 answer
8k views

Rejected emails: Messages with multiple addresses in From: header are not accepted - gsmtp

We host a service which can send emails on behalf of client businesses to end users. These emails must appear to be from the client business, even though they are generated from within our system. We ...
0 votes
1 answer
654 views

To-Recipient Required in Email?

I would like to know if a "To"-Recipient is required in an e-mail per definition or if all recipients could be Bcc or Cc. RFC5322 states The only required header fields are the origination date ...
2 votes
2 answers
101 views

why can the Sender field not be easily configured?

To clarify this and this explanation for Sender:: In brief, From: in the message indicates the mailbox of whoever wrote the message, Sender: indicates the entity which sent a message on behalf ...
16 votes
2 answers
2k views

What's the point of repeating an email address in "The Envelope" and the "The Header"?

I learned that both the FROM address and the TO address is repeated in a hidden element called the "envelope", and then repeated again in the "body". Question Why isn't the envelope data copied into ...