networking – How does the operating system determine the interface to use for a duplicate local link address range?

I have a Linux server with a lot of containers. Each container (with an isolated network namespace) generates a veth interface on the host, and the IPv6 routing table has a lot of entries for fe80::/64, including 4 physical links. When I ping an address in this CIDR block, how does the system discover from which interface the ARP should query?

seo – How to exclude a site address without a URL prefix from being crawled by search engines?

Suppose I have a website on the following domain:

When a user visits, he will be redirected by my script to one of 3 languages, depending on his navigator.language, if it has English default, it would be:, russian: and so on.

But Google, explore the main page of my website without any language prefix, is it possible to exclude robots?

How can I copy the recipient's e-mail address when I compose a new e-mail in Microsoft Outlook for Android?

I compose a new email in Microsoft Outlook for Android and I wish to copy the recipient's email address;

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How can I copy the recipient's e-mail address when I compose a new e-mail in Microsoft Outlook for Android?

Networking – Why can not I ping an external IP address and resolve the DNS from this Ubuntu Linux machine?

I am not so much in networks and systems engineering.

I have an Ubuntu 18.04 virtual machine that sits on a customer's network

1) Can not ping external addresses to the network (but I can ping another machine inside this network so that the ping works).

Here is what I get:

andrea.nobili@VHPLWSO2EI01:~$ ping
PING ( 56(84) bytes of data.

--- ping statistics ---
111 packets transmitted, 0 received, 100% packet loss, time 112647ms

2) I can not solve the address using DNS:

Trying to resolve I get this error:

andrea.nobili@VHPLWSO2EI01:~$ nslookup
;; Got SERVFAIL reply from, trying next server

** server can't find SERVFAIL

But the strange thing that I do not understand is that if I use wget I can download the page (so wget seems to correctly resolve the address):

--2019-12-06 12:51:04--
Connecting to connected.
Proxy request sent, awaiting response... 301 Moved Permanently
Location: (following)
--2019-12-06 12:51:04--
Connecting to connected.
Proxy request sent, awaiting response... 200 OK
Length: unspecified (text/html)
Saving to: ‘index.html.11’

index.html.11                           ( <=>                                                                )  11.72K  --.-KB/s    in 0.009s

2019-12-06 12:51:04 (1.24 MB/s) - ‘index.html.11’ saved (11999)

Another additional information is: there is a proxy. On this machine I have installed cntlm Proxy. This local proxy performs authentication on a Windows system to browse the Internet. Then I export proxy http and https_proxy to point to this local proxy:

export http_proxy=http://USWRNAME:PASSWORD@IP_OF_MACHINE:3128
export https_proxy=https://USWRNAME:PASSWORD@IP_OF_MACHINE:3128

The proxy works fine. If I do not configure the proxy, I can not use wget.

I therefore have the following doubts:

1) Maybe the ping problem related to DNS problem?

2) Why nslookup can not resolve the IP address of while wget seems to be able to do it?

3) Maybe something that is not strictly related to this Linux machine but is linked to the network? I mean something related to the configuration of the router, the DNS or something related to the firewall?

4) In case something could be related to the firewall? From what I know, the firewall is related to the ports (filter ports), but the ping must be on ICMP and does not know the concept of port.

What could be the causes of these two problems? How can I better study or what can I ask the client's system engineer?

linux – The host command resolves the IP address but gives an error to the host not found

I have problems with one of the EC2 instances where the application is dying because it fails to resolve other systems of the same VPC.

When I run host ip- command on a server, I get this answer. has address
Host not found: 3(NXDOMAIN)
Host not found: 3(NXDOMAIN)

When I do ping, I receive the answer.

I suspect something is going wrong in the DNS system, but I have a hard time understanding what might be causing this.

Can you please point me in the right direction?

transactions – how to recover BTC from BCH address

At the technical level, it is possible. You can retrieve a BTC code from a BCH address by importing the private key into a BCH portfolio.

However, for many exchanges, security systems do not allow the deletion of private keys (for example, they can be locked in an HSM or linked by other security checks). They also would not allow the signing of arbitrary transactions in some cases, thus preventing manual recovery.

Your only option is to contact Kraken and ask him to access the private keys in one way or another and sign a transaction for you, which returns the BTC to an address you control. . This may not be possible with their configuration, but it is your best (and only) solution.

The spam that transmits postfix config "the host name does not resolve to address: no address associated with the host name"

On a postfix MX MTA configuration, I do two spam checks, which should absolutely not be the case.

the postfix/smtpd process saves these warnings, which should to be a difficult failure in this configuration:

  • hostname * does not resolve to address *: No address associated with hostname
  • Unable to look up MX host * for Helo command *: No address associated with hostname

The relevant mail log is:

postfix/smtpd: warning: hostname does not resolve to address No address associated with hostname
postfix/smtpd: connect from unknown(
postfix/smtpd: warning: Unable to look up MX host for Helo command No address associated with hostname
policyd-spf: prepend Received-SPF: Neutral (mailfrom) identity=mailfrom; client-ip=;;; receiver=
postgrey: action=greylist, reason=new, client_name=unknown, client_address=,, recipient=

It should not even touch blocking lists or additional checks that would block it later.
Here's why:

  • has a PTR record, but this domain does not have an IP A / AAAA record (or MX record).
  • HELO's has an MX record, but this subdomain does not have an IP A / AAAA record.

I can not find any postconf parameters that could turn these warnings into errors, and I wonder if I should write my own check here.
postfix Is save the warnings, he is aware of the problems, so hope I miss something?

The MTA configuration has

smtpd_delay_reject = yes    
smtpd_helo_required = yes
smtpd_helo_restrictions =


smtpd_sender_restrictions =

and I would have thought that one or the other or both should remove that link, but on closer inspection, these checks seem insufficient here:

rejeter_unknown_helo_hostname: Reject the request when the HELO or EHLO host name does not have a DNS A or MX record.

Clearly, the HELO domain has an A and MX record (only the MX can not resolve). So, that seems to be passing.

refuse_unknown_sender_domain: Reject the request when Postfix is ​​not the final destination of the sender's address and the domain MAIL FROM is not 1) DNS MX and no DNS record A, or 2) a malformed MX record such as a record with a null-length MX hostname

MAIL OF ( is clearly falsified, so it does not help at all?

networking – How to set a static IP address on the command line or in an adb shell?

You can try to use ip order.

How does it compare to ifconfig

To configure an IP address, you can use:

ip address add dev eth0

or the long form

ip addr add broadcast dev eth0

search for the current configuration using

ip addr show

How to find an address that holds balance in Bitcoin Core?

I can not find the address that contains my balance in Bitcoin Core. The balance of all receiving addresses is 0. However, there is a balance in the wallet. How can I find the address that holds this balance?

I sent a bitcoin to a non coinbase email address

How to recover a bitcoin sent to a coinbase e-mail address and that the e-mail address is not registered with coinbase …