I trying to send mails from SMTP server to yahoo but not sending mails and getting below error.
553 5.7.1 [BL21] Connections will not be accepted from IP, because the ip is in Spamhaus's list; see http://postmaster.yahoo.com/550-bl23.html
Is there any chance to remove IP from PBL?
The first thing to know is: the PBL is not a blacklist.
You are not listed for spamming or for anything you have done. The PBL is simply a list of all of the world's dynamic IP space, i.e: IP ranges normally assigned to ISP broadband customers (DSL, DHCP, PPP, cable, dialup). It is perfectly normal for dynamic IP addresses to be listed on the PBL. In fact all dynamic IP addresses in the world should be on the PBL. Even static IPs which do not send mail should be listed in the PBL. (from http://www.spamhaus.org/faq/section/Spamhaus%20PBL#183)
This is also confirmed on the site you've mentioned http://postmaster.yahoo.com/550-bl23.html :
In our continuing efforts to protect our users from unsolicited email, Yahoo Mail doesn't accept SMTP connections from:
Dynamic or residential IP addresses as determined by Spamhaus PBL
Have you turned on 'SMTP AUTHENTICATION'? That might could help, regarding Spamhaus, but it certainly depends more on Yahoos configuration.
Related
Is it possible to ping mininet ip? I found mininet's ip starts with 10.0.2.15 . I can ping from mininet to others. However, I failed to ping other place to mininet. How can I setup this?
10.0.0.0/8, which is 10.0.0.0 - 10.255.255.255 are IP addresses used only locally, they are not accessed from the internet (other networks). Here is some info from IANA:
These addresses are in use by many millions of independently operated networks, which might be as small as a single computer connected to a home gateway, and are automatically configured in hundreds of millions of devices. They are only intended for use within a private context and traffic that needs to cross the Internet will need to use a different, unique address.
These addresses can be used by anyone without any need to coordinate with IANA or an Internet registry. The traffic from these addresses does not come from ICANN or IANA. We are not the source of activity you may see on logs or in e-mail records.
I'm working on a program that tracks when search engines cannot find important files on my server.
From my computer I typed:
nslookup google.com
and I received 11 IP addresses in return all beginning with 74.125.226
I then tried:
dig google.com
and I still receive the same IP addresses.
When I navigate to here through searching: http://www.iplists.com/google.txt, the number of IP addresses is greater than 10 and that list includes ones starting with 64.249 which also appears in my server log.
Am I using the wrong linux tools to find every IP address associated with google? If so, what tools should I use?
I want to generate the IP address database myself rather than rely on someone's post of IP addresses just in case IP addresses are updated in the future.
The keyword here is GeoDNS: When website/service has many servers around the world (with the main purpose of providing the lowest possible latency to user requests), using GeoDNS it can respond with different IP addresses to DNS queries for the same hostname, based on the locaton of the DNS client that is making the query (of course it will try to respond with the IP address of the closest server).
Basically, there is no way you can retrieve all possible addresses just by querying DNS from one location. Also, google can add/remove/change addresses/servers on daily basis so you probably can never have the definite list (unless google publishes it somewhere).
The real-time example, this might help you:
https://www.whatsmydns.net/#A/www.google.com
Additional reading:
What is the difference between Anycast and GeoDNS / GeoIP wrt HA?
If it were possible to retrieve the remote IP from a packet received by my Apache2 server (through a custom plugin perhaps), would it always be guaranteed to be accurate? Or is this value as easy to spoof as the referrer header?
My intended use case is to rate-limit unauthenticated API calls.
If it's a TCP packet, then it'll be accurate as to the sending host. IPs in TCP packets cannot be spoofed unless you've got control of the routers involved. With spoofed source packets, only the initial SYN packet will come back, and then the SYN+ACK response from the server will go to the spoofed address, not wherever the forgery came from - e.g. you cannot do the full 3-way handshake unless you can control packet routing from the targetted machine.
UDP packets, on the other hand, can be trivially forged and you cannot trust anything about them.
As well, even simple things like proxy servers and NAT gateways can cloak the 'real' ip from where the packet originated. You'll get an IP, but it'll be the IP of the gateway/proxy, not the original machine.
It is not reliable. Not only because it can be spoofed, but also because a network element can make your server see a different IP address.
For example, it is very typical in a company to access the Internet through a proxy. Depending on the configuration, from your server point of view, all the different users come from the same IP address.
In any case is a filter you can use in many scenarios. For example, show a captcha when you detect too many login requests from the same IP address.
If your intention is to rate-limit invalid API calls you might want to consider using a service like spamhaus. They list IP's that are likely bots and probes. There are other companies and lists as well. But if your intention is to ever ID the 'bad guy' the source IP is very unlikely to be correct.
If IP addresses can be spoofed by creating false or manipulated http headers, and therefore it should not be relied upon in validating the incoming request in our PHP/ASP pages, how come servers take that and rely on it? For example, denying IPs or allowing them are all based on IP.
do servers get the IP information some other ( and more reliable ) way than say PHP/ASP gets it thru server variables?
Servers are typically willing to rely upon the IP address of a connection for low-risk traffic because setting up a TCP session requires a three-way handshake. This handshake can only succeed if the IP address in the packets is routable and some machine is prepared to handle the connection. A rogue router could fake IP addresses but in general, it is more difficult to fake connections the further away from either endpoint the router is, so most people are prepared to rely on it for low-risk uses. (DNS spoofing is far more likely way to misrepresent a connection endpoint, for example.)
Higher-risk users must use something more like TLS, IPsec, or CIPSO (rare) to validate the connection end-point, or build user authentication onto the lower layers to authenticate specific connections (OpenSSH).
But the actual contents of the TCP session can be anything and everything -- and a server should not rely upon the contents of the TCP session (such as HTTP headers) to faithfully report IP addresses or anything else vital.
IP addresses cannot be spoofed. The address is needed for the server to send a reply.
PHP gets the IP address for its $_SERVER global from the server (hence the variable name!), which determines the address from lower in the protocol stack.
EDIT:
sarnold makes a good point that, in principle, one could corrupt routing tables to misdirect traffic. (Indeed, I believe there was an incident of this in a Tier 1 router in Asia a couple years ago.) So I should clarify that my comment that "IP addresses cannot be spoofed" was narrowly tailored to point out that the server variables will always faithfully reflect the destination IP. What goes on beyond the the server's borders is another matter altogether.
Imagine a user sitting at an Ethernet-connected PC. He has a browser open. He types "www.google.com" in the address bar and hits enter.
Now tell me what the first packet to appear on the Ethernet is.
I found this question here: Interview Questions on Socket Programming and Multi-Threading
As I'm not a networking expert, I'd like to hear the answer (I'd assume it is "It depends" ;) ).
With a tool like Wireshark, I can obviously check my own computers behaviour. I'd like to know whether the packets I see (e.g. ARP, DNS, VRRP) are the same in each ethernet configuration (is it dependent on the OS? the driver? the browser even :)?) and which are the conditions in which they appear. Being on the data-link layer, is it maybe even dependent on the physical network (connected to a hub/switch/router)?
The answers that talk about using ARP to find the DNS server are generally wrong.
In particular, IP address resolution for off-net IP addresses is never done using ARP, and it's not the router's responsibility to answer such an ARP query.
Off-net routing is done by the client machine knowing which IP addresses are on the local subnets to which it is connected. If the requested IP address is not local, then the client machine refers to its routing table to find out which gateway to send the packet to.
Hence in most circumstances the first packet sent out will be an ARP request to find the MAC address of the default gateway, if it's not already in the ARP cache.
Only then can it send the DNS query via the gateway. In this case the packet is sent with the DNS server's IP address in the IP destination field, but with the gateway's MAC address on the ethernet packet.
You can always download wireshark and take a look.
Though to spoil the fun.
Assuming, the IP address of the host is not cached, and the MAC address of the DNS server is not cached, the first thing that will be sent will be a broadcast ARP message trying to find out the MAC address of the DNS server (which the router will respond to with its own address).
Next, the host name will be resolved using DNS. Then the returned IP address will be resolved using ARP (again the router will respond with its own address), and finally, the HTTP message will actually be sent.
Actually, it depends on a variety of initial conditions you left unspecified.
Assuming the PC is running an operating system containing a local DNS caching resolver (mine does), the first thing that happens before any packets are sent is the cache is searched for an IP address. This is complicated, because "www.google.com" isn't a fully-qualified domain name, i.e. it's missing the trailing dot, so the DNS resolver will accept any records already in its cache that match its search domain list first. For example, if your search domain list is "example.com." followed by "yoyodyne.com." then cached resources matching the names "www.google.com.example.com." "www.google.com.yoyodyne.com." and finally "www.google.com." will be used if available. Also note: if the web browser is one of the more popular ones, and the PC is running a reasonably current operating system, and the host has at least one network interface with a global scope IPv6 address assigned (and the host is on a network where www.google.com has AAAA records in its DNS horizon), then the remote address of the server might be IPv6 not IPv4. This will be important later.
If the remote address of the Google web server was locally cached in DNS, and the ARP/ND6 cache contains an entry for the IPv4/IPv6 address (respectively) of a default router, then the first transmitted packet will be a TCP SYN packet sourced from the interface address attached to the router and destined for the cached remote IPv4/IPv6 address. Alternatively, the default router could be reachable over some kind of layer-2 or layer-3 tunnel, in which case, the SYN packet will be appropriately encapsulated.
If the remote address of the Google web server was not locally cached, then the host will first need to query for the A and/or AAAA records in the DNS domain search list in sequence until it gets a positive response. If the first DNS resolving server address in the resolver configuration is in one of the local IPv4 subnet ranges, or in a locally attached IPv6 prefix with the L=1 bit set in the router advertisement, and the ARP/ND6 cache already contains an entry for the address in question, then the first packet the host will send is a direct DNS query for either an A record or a AAAA record matching the first fully-qualified domain name in the domain search list. Alternatively, if the first DNS server is not addressable on-link, and a default router has an ARP/ND6 cache entry already, then the DNS query packet will be sent to the default router to forward to the DNS server.
In the event the local on-link DNS server or a default router (respectively, as the case above may be) has no entry in the ARP/ND6 cache, then the first packet the host will send is either an ARP request or an ICMP6 neighbor solicitation for the corresponding address.
Oh, but wait... it's even more horrible. There are tweaky weird edge cases where the first packet the host sends might be a LLMNR query, an IKE initiation, or... or... or... how much do you really care about all this, buckaroo?
It depends
Got that right. E.g. does the local DNS cache contain the address? If not then a DNS lookup is likely to be the first thing.
If the host name is not in DNS cache nor in hosts file, first packet will go to DNS.
Otherwise, the first packet will be HTTP GET.
Well, whatever you try to do, the first thing happening is some Ethernet protocol related data. Notably, Ethernet adapters have to decide whether the Ethernet bus is available (so there's some collision detection taking place here)
It's hard to answer your question because it depends a lot on the type of ethernet network you're using. More information on Ethernet transmission can be found here and here