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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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 ...
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-2 votes
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How does CRLF work in SMTP protocol?

I'm casually reading through RFC 5312 https://datatracker.ietf.org/doc/html/rfc5321#section-2.3.8 Lines consist of zero or more data characters terminated by the sequence ASCII character "CR&...
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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 ...
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4 votes
1 answer
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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 ...
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1 answer
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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 ...
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0 votes
2 answers
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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 ...
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3 votes
0 answers
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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:...
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3 votes
2 answers
949 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 ...
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-1 votes
2 answers
166 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....
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1 answer
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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 ...
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1 answer
956 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, ...
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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 ...
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1 answer
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Where to find symbol definitions for RFC protocol flow diagram?

I am reading RFC5077, and bumped into following diagram: ClientHello (empty SessionTicket extension)--------> ServerHello ...
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1 answer
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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 ...
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0 votes
1 answer
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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 ...
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2 votes
1 answer
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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 ...
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2 votes
3 answers
801 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@...
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1 answer
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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 ...
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How many DHCP Pad Option Bytes should be added?

RFC 1553 (DHCP Options) states: 3.2. End Option The end option marks the end of valid information in the vendor field. Subsequent octets should be filled with pad options. The code for the ...
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0 votes
1 answer
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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 ...
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-3 votes
1 answer
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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,...
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4 votes
1 answer
84 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. ...
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3 votes
1 answer
453 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 ...
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1 answer
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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. ...
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2 votes
1 answer
1k 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 ...
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1 vote
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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 ...
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3 votes
1 answer
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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-...
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1 vote
1 answer
200 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 ...
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-1 votes
1 answer
518 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 ...
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0 votes
1 answer
875 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" ...
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1 vote
1 answer
183 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 ...
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0 votes
1 answer
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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, ...
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0 votes
1 answer
670 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 ...
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2 votes
1 answer
7k 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 ...
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0 votes
1 answer
289 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 ...
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2 votes
2 answers
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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 ...
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15 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 ...
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1 vote
1 answer
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Does a ccTLD/gTLD give out response from cache (or use cache)?

The question is exactly the same as the title says. Does the ccTLD/gTLD (and root servers come into the scenario automatically i presume) use cache? And what type of response it supplies? I know ...
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1 vote
1 answer
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Debate with Microsoft on RFC 1918 when setting up a VPN to Azure

Microsoft has a technology called "point to site" VPN. (reference1, reference2) I have the following internal class "A" networks defined on premise: 10.2.0.0/16 10.4.0.0/16 10.40.0.0/16 10.20.0.0/...
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1 vote
1 answer
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What is the format of the NAME field in the DNS answer section?

The NAME field is not detailed completely in RFC 1035 section 4.1.3. I want to understand this field (programmatically) for the ANSWER message type and I searched these resources (datasheet) for that....
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6 votes
2 answers
11k 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 ...
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2 votes
2 answers
3k 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 ...
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0 votes
0 answers
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IMAP woes when moving to new Exchange

We've recently moved to a semi-outsourced Exchange farm, replacing our internal one. An application I've been asked to help troubleshoot uses IMAP to download some emails from the Exchange servers in ...
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11 votes
2 answers
2k 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, ...
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44 votes
2 answers
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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 ...
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1 answer
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Sendmail support of empty group addresses (AKA list syntax)

E-mail group addresses such as undisclosed-recipients:; or a group:<u1@example.net>,<u@x.example.net>; are valid forms of addressing according to RFC 5322, see for instance the ...
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-1 votes
2 answers
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Is RFC1035s definition of a <domain-name> wrong?

[RFC1035] defines <domain-name> as <domain-name> is a domain name represented as a series of labels, and terminated by a label with zero length. This means a <domain-name> must be a ...
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18 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. ...
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1 vote
2 answers
488 views

Is smart hosting to an A record a violation of RFC-5321 section 1?

I have a sendmail server configured to smarthost to a downstream resource. The configuration is currently: define(`SMART_HOST',`relay:[vip.example.local]')dnl Since it's sending the A record for ...
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1 vote
1 answer
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ICMP replies - ingress or egress interface (e.g. from a traceroute)

When a traceroute is initiated and receives an ICMP reply from the nodes, which interface should the be replying be from according to RFC 1812. they are actually replying from ingress (where they ...
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