Ip Any
0.0.0.0 – Wikipedia
In the Internet Protocol Version 4, the address 0. 0. 0 is a non-routable meta-address used to designate an invalid, unknown or non-applicable target. This address is assigned specific meanings in a number of contexts, such as on clients or on servers. [1]
As a host address
Uses include:[2][circular reference]
A way to specify “any IPv4 address at all”. It is used in this way when configuring servers (i. e. when binding listening sockets). This is known to TCP programmers as INADDR_ANY. (bind(2) binds to addresses, not interfaces. )
The address a host claims as its own when it has not yet been assigned an address. Such as when sending the initial DHCPDISCOVER packet when using DHCP.
The address a host assigns to itself when address request via DHCP has failed, provided the host’s IP stack supports this. This usage has been replaced with the APIPA mechanism in modern operating systems.
A way to explicitly specify that the target is unavailable. [3]
A way to route a request to a nonexistent target instead of the original target. Often used for adblocking purposes.
In the context of servers, 0. 0 can mean “all IPv4 addresses on the local machine”. If a host has two IP addresses, 192. 168. 1. 1 and 10. 2. 1, and a server running on the host is configured to listen on 0. 0, it will be reachable at both of those IP addresses.
Routing
In the context of routing tables, a network destination of 0. 0 is used with a network mask of 0 to depict the default route as a destination subnet. This destination is expressed as 0. 0/0 in CIDR notation. It matches all addresses in the IPv4 address space and is present on most hosts, directed towards a local router.
In routing tables, 0. 0 can also appear in the gateway column. This indicates that the gateway to reach the corresponding destination subnet is unspecified. This generally means that no intermediate routing hops are necessary because the system is directly connected to the destination. [4]
In IPv6
In IPv6, the all-zeros address is typically represented by:: (two colons), which is the short notation of 0000:0000:0000:0000:0000:0000:0000:0000. [5] The IPv6 variant serves the same purpose as its IPv4 counterpart.
See also
Reserved IP addresses
localhost
References
^ Bradley Mitchell (16 December 2018). “What It Means When You See the 0. 0 IP Address”. Lifewire. Retrieved 25 March 2019.
^ Akemi Iwaya (16 August 2015). “What is the Difference Between 127. 1 and 0. 0? “. How-To Geek. Retrieved 25 March 2019.
^
“Cable Device Management Information Base for Data-Over-Cable Service Interface Specification (DOCSIS) Compliant Cable Modems and Cable Modem Termination Systems”. If 0. 0, either syslog transmission is inhibited, or the Syslog server address is not an IPv4 address.
^ Sandra Henry-Stocker (3 August 2013). “Unix: Getting from here to there (routing basics)”. Network World. Retrieved 25 March 2019.
^ Das, Kaushik. “IPv6 Addressing”. Retrieved 18 June 2015.
In RFC 1122 the notation “{0, 0}” is used to designate 0. 0/x (x being anything from 0 to 32). Quote: “{ 0, 0} This host on this network. MUST NOT be sent, except as a source address as part of an initialization procedure by which the host learns its own IP address. ”
External links
“Special Use IPv4 Addresses”. IETF.
Permit ANY ANY ; What do you permit? – Firewalls – Spiceworks …
Permit ANY ANY; What do you permit? – Firewalls – Spiceworks
Home
Security
Firewalls
I’m reviewing some ACLs on a firewall (not set up by me). At the bottom of the inside interface, they put a PERMIT ANY ANY. I believe it was done because the team who set it up was contractors and didn’t want to return. It’s my understanding that this is bad practice.
What ACL rules do you use to give your users internet access?
Popular Topics in Firewalls
Which of the following retains the information it’s storing when the system power is turned off?
ROM
CPU
RAM
GPU
88% of IT pros got this right.
17 Replies
Only what they need.
Port 80, 443 outbound, assuming that any connections originating in your network are allowed back in.
And add to the list as users report being unable to access sites.
So are you saying the rule is generally ANY ANY but only for 80, 443? Or do you filter down the ANY ANY also?
I generally block the specific things that need to get blocked, then permit everything else. I don’t care so much about what goes out, within reason.
The Permit ACL would go after all the Deny ACLs since they get hit top to bottom. Then keep in mind there could be an inherent Deny, so without the Permit Any Any, you’ll just be blocking everything.
Deny stuff
Permit Everything else
Inherent Deny
Thanks guys.
The reason this even came about is because I’m having some communications issues between two networks. Say for example I have Network A and Network B. Network A has a higher security level than Network B. Because of the ANY ANY PERMIT IP rule, all traffic was being allowed from Network B (lower security) to Network A (higher security).
Permit what you explicitly want to allow
Deny everything else.
This would be the Best Practice but it is more work to get set up and maintain. It’s also more secure, although never 100%.
Yup – a permit IP any any statement will allow all IP traffic to flow across the interface. Keep in mind that there is an implicit deny ip any any at the end of any access list, so a permit statement tells the router what to allow across the interface and denies all other IP traffic.
Kenny8416
This person is a verified professional.
Verify your account
to enable IT peers to see that you are a professional.
May 12, 2015 at 15:32 UTC
Yup, normally a firewall would have a deny any any as a catchall as the lowest rule in the chain.
My guess is the contractors who set it up couldn’t get something working so just changed deny to permit and left it.
Deny all as a default then add the permit rules you need is best practice.
Jerry (ThreatTrack) wrote:
Not sure I agree with this, certainly not that way on Sonicwall.
I may have been a little too generalizing and I’m not sure about Sonicwall. On a Cisco device, if you are only wishing to allow a specific subnet, for instance, then a simple ACL with a permit statement will do and any other traffic will be denied. However, if there are specific addresses (or protocols, etc) in the subnet which should be denied, the deny statements would come first, then the permit subnet statement would come next. Anything else not covered by a permit statement will be influenced by the implicit deny at the end.
As Steve612 stated above:
Permit everything else
Implicit deny
One could do it the other way around – specific permit statements for only the things you want to allow. Sure, more secure, but in most cases a much longer ACL which could, in turn, produce more latency across the interface.
Still doesn’t make sense to me, but I’m not a Cisco ACL guy.
Explicit deny (say, FTP)
Then allow everything.
Then Deny everything of which there is none because it was all just allowed.
So in reality it’s just block what you don’t want and allow everything else in/out.
One should do it the other way around. Explicitly allow traffic and deny everything else.
Basically every packet crossing the interface will be compared to each rule (statement) in the ACL from top to bottom until it meets a rule that applies, then the packet is either permitted or denied(dropped), so you should put your more granular rules first. If the packet gets to the end of the ACL and has not met a rule that applies (either permit or deny), the packet is dropped.
Brand Representative for AT&T Cybersecurity
It’s been many years since I touched firewalls (thankfully! ) but we always defaulted to deny and never had the any-any in place. But being a bank with a large complex network and many firewalls we’d spend hours and hours trying to troubleshoot where issues were occurring and trying to resolve them without opening up too many holes in the firewall.
A few years later after I moved onto another role, I caught up with some old colleagues who said that they’d invested in a tool to automatically analyse the rules and network configuration and it had made their life a whole lot easier. I believe they were using Skybox Security, although I assume Tufin, Algosec or RedSeal would have been similar.
I guess what I’m saying is that if you have a complex network and multiple firewalls, then a tool can be of use. Unless you’re a contractor charging by the day… in which case keep it manual;)
Little Green Man
May 13, 2015 at 02:31 UTC
I’ve never done ANY ANY. Defeats the purpose of having a firewall appliance.
May 13, 2015 at 08:33 UTC
I’ve never seen a firewall configured the way Jerry is stating. If youo have explicit denies followed by a Permit ANY ANY, then anything you’ve not thought of to deny will be allowed through. I’m not sure I’m confident enough in my knowledge of all IP’s and port types to be certain I have denied every possible attack vector. As Limey point our, the final Implicit deny in Jerry’s model is pointless, as it will never be reached, since the rule above it allows everything.
The only Permit ANY ANY rules I see are from More to Less secure networks i. e anything on your internal can get out to the DMZ or external. You might want an explicit deny in that direction (e. g SMTP only allowed out from your mail server)
IMO it’s best to block everything as the default, then open the addresses and ports as required, that way anything you forget will cause a failure, not a security breach.
Michael Quaintance
May 13, 2015 at 09:52 UTC
Just like Little Green Man has said, I’d never use a permit any any. Defeats the purpose of access control in my book.
After thinking about this for a while, I think it’s just a wording problem in the post by Steve above, and then quoted by Jerry. Here’s my version:
Explicit Deny (block stuff that you know of and don’t want, saves having to go through the allow rules to reach the Deny All)
Explicit Allow (allow just what you want)
Implicit Deny (Deny everything that didn’t have a match)
Nicholas, can you mark BA and HP’s?
I think there was a misunderstanding regarding my statement ” Yup – a permit IP any any statement will allow all IP traffic to flow across the interface. ”
I was not suggesting the use of a permit any any statement – that would be ludicrous. I was agreeing with someone prior that the permit any any would allow ALL traffic.
This topic has been locked by an administrator and is no longer open for commenting.
To continue this discussion, please
ask a new question.
IPAddress.Any Field (System.Net) | Microsoft Docs
Field () | Microsoft Docs
Skip to main content
This browser is no longer supported.
Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support.
Definition
In this article
Provides an IP address that indicates that the server must listen for client activity on all network interfaces. This field is read-only.
public: static initonly System::Net::IPAddress ^ Any;
public static readonly Any;
staticval mutable Any:
Public Shared ReadOnly Any As IPAddress
Field Value
IPAddress
Remarks
The method uses the Any field to indicate that a Socket instance must listen for client activity on all network interfaces.
The Any field is equivalent to 0. 0. 0 in dotted-quad notation.
Applies to
Frequently Asked Questions about ip any
What does permit IP any any mean?
Yup – a permit IP any any statement will allow all IP traffic to flow across the interface. Keep in mind that there is an implicit deny ip any any at the end of any access list, so a permit statement tells the router what to allow across the interface and denies all other IP traffic.May 11, 2015
What is IPAddress any?
Provides an IP address that indicates that the server must listen for client activity on all network interfaces. This field is read-only. public: static initonly System::Net::IPAddress ^ Any; C# Copy.
What is the 0.0 0.0 IP address?
In the Internet Protocol Version 4, the address 0.0. 0.0 is a non-routable meta-address used to designate an invalid, unknown or non-applicable target. This address is assigned specific meanings in a number of contexts, such as on clients or on servers.
