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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Cseq RFC comparison and understanding

I have a below call flow, wherein I have some confusion related to CSEQ..... A --INVITE CSEQ-1-> B A <--180 CSEQ-1 --- B A --PRACK CSEQ-2-> B A <--183 CSEQ-1 --- B A --PRACK CSEQ-3-> B ...
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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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28 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 ...
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284 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 ...
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How should an SMTP server handle quoted and escaped postmaster recipients?

RCPT TO: <"po\S\tMaStE\R"> RCPT TO: <"\pOSTmasT\eR"@example.com> Are those valid and considered to be the Postmaster recipient? Why is it?
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108 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 ...
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1answer
61 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 ...
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3answers
137 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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1answer
133 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 ...
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79 views

List-Unsubscribe as defined in RFC 2369

Odoo (v11 that I use) does not support RFC 2369. My question: How can I add unsubscribe link with both the email and the http links? ==================================================================...
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DHCP Boot File Size Option

The description of the Boot File Size Option in RFC 2132 is not very useful: https://tools.ietf.org/html/rfc2132#section-3.15 3.15. Boot File Size Option This option specifies the length in ...
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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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1answer
76 views

rfc3207 smtp starttls restriction confusion

From https://tools.ietf.org/html/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 ...
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1answer
112 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,...
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1answer
74 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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1answer
141 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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1answer
64 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. ...
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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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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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1answer
1k 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-...
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1answer
123 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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1answer
336 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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1answer
575 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" header: From: =?iso-...
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1answer
145 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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1answer
10k 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, ...
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1answer
463 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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1answer
4k 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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1answer
106 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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2answers
77 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 ...
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2answers
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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1answer
64 views

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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1answer
285 views

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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1answer
736 views

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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2answers
7k 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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2answers
2k 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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38 views

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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2answers
1k 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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2answers
2k 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 ...
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1answer
794 views

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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2answers
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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 ...
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2answers
2k 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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2answers
342 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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1answer
2k views

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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1answer
8k 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 ...
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1answer
585 views

Is Strict-Transport-Security HTTP header name case-sensitive?

I'm digging into the HTTP Strict-Transport-Security specification, https://tools.ietf.org/html/rfc6797 It specifies the syntax of the header like this: Strict-Transport-Security: max-age=15768000 ; ...
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264 views

Unable to get structured data in logged messages even after adding mmpstrucdata and mmrfc5424addhmac?(RFC5424)

I am trying to log messages with structured data . But it is showing null value for structured data. I am working with rsyslog 8.9.0.Can someone tell me either i need to load some module or modify ...
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1answer
463 views

Apache set max Content-Range

The Question: Client asks for: Range:bytes=0- Server responds with: Content-Length:8396748 Content-Range:bytes 0-8396747/8396748 I want to limit that Content-Range to 1MB chunks so the server ...
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0answers
2k views

Does a ping to 127.0.0.1 hit the network card? Which RFC / standard states that? [closed]

I recently did an exam where one of the questions stated that you can run ping 127.0.0.1 on a computer to verify if its network card is working. I have already read on multiple sources that this ...
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3answers
160 views

What to do if one doesn't want to receive email bounces?

Background—the standards RFC 5321 §4.5.5 states: All other types of messages (i.e., any message which is not required by a Standards-Track RFC to have a null reverse-path) SHOULD be sent with ...
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1answer
1k views

Replacing an MX record with a CNAME that doesn't match the hostname

Today we have 5 companies that all use Google for email services example1.com. 3w IN MX 10 mail.Google.com. example2.com. 3w IN MX 10 mail.Google.com. example3.com....