IP 0.0.0.0/0 - 0.0.0.0/32 - TCP-IP

This is a discussion on IP 0.0.0.0/0 - 0.0.0.0/32 - TCP-IP ; Hi Any useful link that explains this IP address range in details, please? Thanks in advance! The Dude...

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Thread: IP 0.0.0.0/0 - 0.0.0.0/32

  1. IP 0.0.0.0/0 - 0.0.0.0/32

    Hi

    Any useful link that explains this IP address range in details, please?

    Thanks in advance!

    The Dude



  2. Re: IP 0.0.0.0/0 - 0.0.0.0/32

    In article ,
    The Dude Dude@thedu.de> wrote:

    >Any useful link that explains this IP address range in details, please?


    Urrr -- 0.0.0.0/0 is the *entire* IPv4 address range, and
    0.0.0.0/32 is just the single IPv4 address 0.0.0.0.

    For any given network, the lowest address in the network is
    reserved. Historically, the lowest address was one of the two
    allowed choices for the broadcast address; later, the broadcast
    address was standardized as being the highest address in the
    network only.

    You should only see traffic coming from the lowest address in
    a network if the link is a point-to-point link and the network is
    either a /31 or a /32.

    One exception to that is that when a system is DHCP'ing,
    it does not yet know its IP address, and so it is allowed to
    use the IP address 0.0.0.0 as its source IP.

  3. Re: IP 0.0.0.0/0 - 0.0.0.0/32


    "Walter Roberson" wrote in message
    news:8B7Hg.459285$IK3.362963@pd7tw1no...
    > In article ,
    > The Dude Dude@thedu.de> wrote:
    >
    >>Any useful link that explains this IP address range in details, please?

    >
    > Urrr -- 0.0.0.0/0 is the *entire* IPv4 address range, and
    > 0.0.0.0/32 is just the single IPv4 address 0.0.0.0.
    >


    As you know, subnet masks use 1s to match the bits and 0 to ignore the bits;
    1s indicate the network portion and 0s indicate the host portion of the IP
    address. Now, IP address 0.0.0.0/0 is considered the default ip route,
    whereas IP address 0.0.0.0/32 means _ any network_ with _any mask. I wish I
    could found some study material on this particular subject ...

    The Dude



  4. Re: IP 0.0.0.0/0 - 0.0.0.0/32

    In article <9L8Hg.448204$iF6.409035@pd7tw2no>,
    The Dude Dude@thedu.de> wrote:
    >As you know, subnet masks use 1s to match the bits and 0 to ignore the bits;
    >1s indicate the network portion and 0s indicate the host portion of the IP
    >address.


    True, but you didn't use any subnet masks in your question.
    You used CIDR notation, not masks.

    >Now, IP address 0.0.0.0/0 is considered the default ip route,


    Yes.

    >whereas IP address 0.0.0.0/32 means _ any network_ with _any mask.


    I've never seen 0.0.0.0/32 used for -anything-, but I see in
    RFC 3330 that

    0.0.0.0/8 - Addresses in this block refer to source hosts on "this"
    network. Address 0.0.0.0/32 may be used as a source address for this
    host on this network; other addresses within 0.0.0.0/8 may be used to
    refer to specified hosts on this network [RFC1700, page 4].

    Definitely not "any network with any mask".

    0.0.0.0/32 is 0.0.0.0 with a netmask which has 32 leading 1's. By
    your explanation, the leading 1's are the network portion. There isn't
    any room left for a host mask, so 0.0.0.0/32 cannot be
    "any network with any mask": it means one very specific network with
    one very specific mask.


    >I wish I
    >could found some study material on this particular subject ...


    I'm not sure what kind of material you are looking for? RFC 3330 is
    "Special-Use IPv4 Addresses".

  5. Re: IP 0.0.0.0/0 - 0.0.0.0/32


    "Walter Roberson" wrote in message
    news:CD9Hg.448475$iF6.189742@pd7tw2no...
    > In article <9L8Hg.448204$iF6.409035@pd7tw2no>,
    > The Dude Dude@thedu.de> wrote:
    >>As you know, subnet masks use 1s to match the bits and 0 to ignore the
    >>bits;
    >>1s indicate the network portion and 0s indicate the host portion of the IP
    >>address.

    >
    > True, but you didn't use any subnet masks in your question.
    > You used CIDR notation, not masks.



    isn't 0.0.0.0/0 the same as 0.0.0.0 0.0.0.0 and 0.0.0.0/32 the same as
    0.0.0.0 255.255.255.255 ?


    >
    >>Now, IP address 0.0.0.0/0 is considered the default ip route,

    >
    > Yes.
    >
    >>whereas IP address 0.0.0.0/32 means _ any network_ with _any mask.

    >
    > I've never seen 0.0.0.0/32 used for -anything-,




    0.0.0.0 255.255.255.255 is used for IP routing .



    but I see in
    > RFC 3330 that
    >
    > 0.0.0.0/8 - Addresses in this block refer to source hosts on "this"
    > network. Address 0.0.0.0/32 may be used as a source address for this
    > host on this network; other addresses within 0.0.0.0/8 may be used to
    > refer to specified hosts on this network [RFC1700, page 4].




    I have seen that and it does not tell me much.



    >
    > Definitely not "any network with any mask".
    >
    > 0.0.0.0/32 is 0.0.0.0 with a netmask which has 32 leading 1's. By
    > your explanation, the leading 1's are the network portion. There isn't
    > any room left for a host mask, so 0.0.0.0/32 cannot be
    > "any network with any mask": it means one very specific network with
    > one very specific mask.


    The Dude



  6. Re: IP 0.0.0.0/0 - 0.0.0.0/32


    The Dude wrote:

    > isn't 0.0.0.0/0 the same as 0.0.0.0 0.0.0.0 and 0.0.0.0/32 the same as
    > 0.0.0.0 255.255.255.255 ?


    Yes. So it doesn't mean "any network with any mask". It means the exact
    IP address 0.0.0.0. Since the subnet mask is all 1's, all the bits are
    matched. So the only IP address that matches is 0.0.0.0. 0.0.0.1
    doesn't match because the last bit differs and the last bit must match
    because there's a '1' in that bit position in the mask.

    Similarly, 0.0.0.0/8 is the same as 0.0.0.0 with a mask of 255.0.0.0.
    This means the first octet must match but the last three need not. So
    this network includes 0.1.0.9 but not 1.0.0.0.

    DS


  7. Re: IP 0.0.0.0/0 - 0.0.0.0/32

    roberson@hushmail.com (Walter Roberson) writes:
    > >whereas IP address 0.0.0.0/32 means _ any network_ with _any mask.

    >
    > I've never seen 0.0.0.0/32 used for -anything-, but I see in


    It's INADDR_ANY -- it usually means "no such host."

    > RFC 3330 that
    >
    > 0.0.0.0/8 - Addresses in this block refer to source hosts on "this"
    > network. Address 0.0.0.0/32 may be used as a source address for this
    > host on this network; other addresses within 0.0.0.0/8 may be used to
    > refer to specified hosts on this network [RFC1700, page 4].


    Another common use for 0.0.0.0/8 is to designate ifIndex numbers, as
    for the "Link Data" value in OSPF, and for some BSD-ish interfaces.

    --
    James Carlson, KISS Network
    Sun Microsystems / 1 Network Drive 71.232W Vox +1 781 442 2084
    MS UBUR02-212 / Burlington MA 01803-2757 42.496N Fax +1 781 442 1677

  8. Re: IP 0.0.0.0/0 - 0.0.0.0/32

    The Dude wrote:
    [snip: ip addressing]
    .. I wish I could found some study material on
    > this particular subject ...


    google for it.
    http://www.networkclue.com/routing/t...ddressing.aspx comes up as
    does many other sites.



    --

    hsb


    "Somehow I imagined this experience would be more rewarding" Calvin
    **************************ROT13 MY ADDRESS*************************
    Due to the volume of email that I receive, I may not be able to
    reply to emails sent to my account. Please post a followup instead.
    ************************************************** ******************

  9. Re: IP 0.0.0.0/0 - 0.0.0.0/32


    "Hansang Bae" wrote in message
    news:TUtHg.46178$u05.39618@news-wrt-01.rdc-nyc.rr.com...
    > The Dude wrote:
    > [snip: ip addressing]
    > . I wish I could found some study material on
    >> this particular subject ...

    >
    > google for it.
    > http://www.networkclue.com/routing/t...ddressing.aspx comes up as
    > does many other sites.


    This link does not deal with my subject, but thanks anyway....
    FYI, before I ask here, I search engines, google included, but I am not
    always lucky ...

    Regarding my statement 0.0.0.0 (any network) 255.255.255.255 (any mask), I
    was refering to ACL wildcard ... My bad.
    ACL and OSPF use wildcards which are opposite of normal subnet masks (I
    wonder why) ....

    Thanks for the feedback.

    The Dude



  10. Re: IP 0.0.0.0/0 - 0.0.0.0/32


    The Dude wrote:

    > Regarding my statement 0.0.0.0 (any network) 255.255.255.255 (any mask), I
    > was refering to ACL wildcard ... My bad.
    > ACL and OSPF use wildcards which are opposite of normal subnet masks (I
    > wonder why) ....


    I think the theory is that wildcards are more flexible. For example,
    suppose you want to block all addresses of the form 216.152.*.255. You
    can do that with wildcards but not with subnet masks.

    It may also just be a closer match with how they "think" internally.

    DS


  11. Re: IP 0.0.0.0/0 - 0.0.0.0/32

    In article <1156480229.830288.152470@i42g2000cwa.googlegroups. com>,
    David Schwartz wrote:

    >The Dude wrote:


    >> Regarding my statement 0.0.0.0 (any network) 255.255.255.255 (any mask), I
    >> was refering to ACL wildcard ... My bad.
    >> ACL and OSPF use wildcards which are opposite of normal subnet masks (I
    >> wonder why) ....


    >I think the theory is that wildcards are more flexible. For example,
    >suppose you want to block all addresses of the form 216.152.*.255. You
    >can do that with wildcards but not with subnet masks.


    Yes you can. You can't do it with CIDR notation, but subnet masks
    are not required to use consequative bits.


    >It may also just be a closer match with how they "think" internally.


    Not even necessarily that. Reversing the mask logic for access lists
    may have originally simply been intended to prevent confusion.
    Subnet masks carry with them the implication that the first and
    last addresses in the induced range are reserved for broadcast
    traffic, so to avoid having people ask about that over and over again,
    they may have chosen to use a distinctly different convention that
    did not have that baggage.

  12. Re: IP 0.0.0.0/0 - 0.0.0.0/32

    In article ,
    The Dude Dude@thedu.de> wrote:

    >Regarding my statement 0.0.0.0 (any network) 255.255.255.255 (any mask), I
    >was refering to ACL wildcard ... My bad.
    >ACL and OSPF use wildcards which are opposite of normal subnet masks (I
    >wonder why) ....


    I haven't looked at OSPF in a long time, so I cannot comment on that.

    ACL, "access control lists", are done differently by different
    manufacturers and different software products. 0.0.0.0 255.255.255.255
    as meaning "all IP addresses", is typical in Cisco IOS "extended"
    access lists. There is no standard about that, it's just what
    Cisco IOS uses. Cisco's PIX and ASA security appliances use the same
    bit convention as for subnet masks.

  13. Re: IP 0.0.0.0/0 - 0.0.0.0/32

    The Dude wrote:
    > This link does not deal with my subject, but thanks anyway....
    > FYI, before I ask here, I search engines, google included, but I am
    > not always lucky ...
    >
    > Regarding my statement 0.0.0.0 (any network) 255.255.255.255 (any
    > mask), I was refering to ACL wildcard ... My bad. ACL and OSPF use
    > wildcards which are opposite of normal subnet masks (I wonder why)



    Wildcards are easy to master if (and only if) you convert the IPs to
    binary numbers. If you understand the logic of binary AND and binary
    OR operations, it will become crystal clear. Breaking it down to
    binary numbers is the only way to calculate complicated acls. But this
    topic is better suited for comp.dcom.sys.cisco.

    --

    hsb


    "Somehow I imagined this experience would be more rewarding" Calvin
    **************************ROT13 MY ADDRESS*************************
    Due to the volume of email that I receive, I may not be able to
    reply to emails sent to my account. Please post a followup instead.
    ************************************************** ******************

  14. Re: IP 0.0.0.0/0 - 0.0.0.0/32


    "Hansang Bae" wrote in message
    news:yrOHg.24771$v82.5419@news-wrt-01.rdc-nyc.rr.com...
    > The Dude wrote:
    >> This link does not deal with my subject, but thanks anyway....
    >> FYI, before I ask here, I search engines, google included, but I am
    >> not always lucky ...
    >>
    >> Regarding my statement 0.0.0.0 (any network) 255.255.255.255 (any
    >> mask), I was refering to ACL wildcard ... My bad. ACL and OSPF use
    >> wildcards which are opposite of normal subnet masks (I wonder why)

    >
    >
    > Wildcards are easy to master if (and only if) you convert the IPs to
    > binary numbers. If you understand the logic of binary AND and binary
    > OR operations, it will become crystal clear. Breaking it down to
    > binary numbers is the only way to calculate complicated acls. But this
    > topic is better suited for comp.dcom.sys.cisco.
    >

    I do not know about the details, but I find it easy by reversing the normal
    subnet mask, i.e.:
    the wild card for A.B.C.D/ 27 (255.255.255.224) is 0.0.0.31 (255-224)

    The Dude



  15. Re: IP 0.0.0.0/0 - 0.0.0.0/32

    On Sat, 26 Aug 2006, in the Usenet newsgroup comp.protocols.tcp-ip, in article
    , The Dude wrote:

    >"Hansang Bae" wrote


    >> Wildcards are easy to master if (and only if) you convert the IPs to
    >> binary numbers. If you understand the logic of binary AND and binary
    >> OR operations, it will become crystal clear.


    Agreed - once you understand the binary, hex or CIDR is a piece of cake.

    >I do not know about the details, but I find it easy by reversing the normal
    >subnet mask, i.e.:
    >the wild card for A.B.C.D/ 27 (255.255.255.224) is 0.0.0.31 (255-224)


    1518 An Architecture for IP Address Allocation with CIDR. Y. Rekhter,
    T. Li. September 1993. (Format: TXT=72609 bytes) (Status: PROPOSED
    STANDARD)

    1519 Classless Inter-Domain Routing (CIDR): an Address Assignment and
    Aggregation Strategy. V. Fuller, T. Li, J. Yu, K. Varadhan. September
    1993. (Format: TXT=59998 bytes) (Obsoletes RFC1338) (Status: PROPOSED
    STANDARD)

    1878 Variable Length Subnet Table For IPv4. T. Pummill, B. Manning.
    December 1995. (Format: TXT=19414 bytes) (Obsoletes RFC1860) (Status:
    INFORMATIONAL)

    RFCs are available on very many web sites - three examples being

    http://www.ietf.org/rfc/rfc0000.txt
    http://www.faqs.org/rfcs/rfc0000.html
    http://www.rfc-editor.org/rfc/rfc0000.txt

    replace the four zeros with the four digit RFC number.

    Old guy

  16. Re: IP 0.0.0.0/0 - 0.0.0.0/32

    The Dude wrote:
    [Cisco wildcards for ACLs]
    > I do not know about the details, but I find it easy by reversing the
    > normal subnet mask, i.e.: the wild card for A.B.C.D/ 27
    > (255.255.255.224) is 0.0.0.31 (255-224)


    And what will you do if someone asks you to create an ACL that will
    block every fourth host on a /26 network? i.e. x.x.x.4, x.x.x.68,
    x.x.x.132, x.x.x.196 but permit others?

    Of course you can use four denies at the top and permit the block, but
    for education sake, what if I told you that you can do this with one
    line?

    permit ip x.x.x.4 255.255.255.192 is the line you're looking for.

    You really can't do this in your head w/o breaking it down into binary
    numbers.

    Before someone jumps in, yes, sometimes engineering elegance can lead
    to operational confusion. But this example is just that, an example.

    --

    hsb


    "Somehow I imagined this experience would be more rewarding" Calvin
    **************************ROT13 MY ADDRESS*************************
    Due to the volume of email that I receive, I may not be able to
    reply to emails sent to my account. Please post a followup instead.
    ************************************************** ******************

  17. Re: IP 0.0.0.0/0 - 0.0.0.0/32


    "Hansang Bae" wrote in message
    news:6jNIg.47239$u05.11356@news-wrt-01.rdc-nyc.rr.com...
    > The Dude wrote:
    > [Cisco wildcards for ACLs]
    >> I do not know about the details, but I find it easy by reversing the
    >> normal subnet mask, i.e.: the wild card for A.B.C.D/ 27
    >> (255.255.255.224) is 0.0.0.31 (255-224)

    >
    > And what will you do if someone asks you to create an ACL that will
    > block every fourth host on a /26 network? i.e. x.x.x.4, x.x.x.68,
    > x.x.x.132, x.x.x.196 but permit others?


    >
    > Of course you can use four denies at the top and permit the block, but
    > for education sake, what if I told you that you can do this with one
    > line?
    >
    > permit ip x.x.x.4 255.255.255.192 is the line you're looking for.



    The wild card should be 0.0.0.63.


    >
    > You really can't do this in your head w/o breaking it down into binary
    > numbers.



    I have imagination the same way a chess player can play the entire game
    blindfold.

    The Dude



  18. Re: IP 0.0.0.0/0 - 0.0.0.0/32


    "The Dude" Dude@thedu.de> wrote in message
    news:TdQIg.492503$IK3.360274@pd7tw1no...
    >
    > "Hansang Bae" wrote in message
    > news:6jNIg.47239$u05.11356@news-wrt-01.rdc-nyc.rr.com...
    >> The Dude wrote:
    >> [Cisco wildcards for ACLs]
    >>> I do not know about the details, but I find it easy by reversing the
    >>> normal subnet mask, i.e.: the wild card for A.B.C.D/ 27
    >>> (255.255.255.224) is 0.0.0.31 (255-224)

    >>
    >> And what will you do if someone asks you to create an ACL that will
    >> block every fourth host on a /26 network? i.e. x.x.x.4, x.x.x.68,
    >> x.x.x.132, x.x.x.196 but permit others?


    First of all, there are only 3 subnetworks on a /26 network , not 4!

    x.x.x.0, x.x.x.64, and x.x.x.128


    >>
    >> Of course you can use four denies at the top and permit the block, but
    >> for education sake, what if I told you that you can do this with one
    >> line?
    >>
    >> permit ip x.x.x.4 255.255.255.192 is the line you're looking for.


    I do not see how your line can block every 4 th host and how your line can
    be any different than

    "permit ip x.x.x.4 0.0.0.63". Note: ACL uses wildcards.

    The Dude



  19. Re: IP 0.0.0.0/0 - 0.0.0.0/32

    In article , "The Dude" Dude@thedu.de> writes:
    >
    > "The Dude" Dude@thedu.de> wrote in message
    > news:TdQIg.492503$IK3.360274@pd7tw1no...
    >>
    >> "Hansang Bae" wrote in message
    >> news:6jNIg.47239$u05.11356@news-wrt-01.rdc-nyc.rr.com...
    >>> The Dude wrote:
    >>> [Cisco wildcards for ACLs]
    >>>> I do not know about the details, but I find it easy by reversing the
    >>>> normal subnet mask, i.e.: the wild card for A.B.C.D/ 27
    >>>> (255.255.255.224) is 0.0.0.31 (255-224)
    >>>
    >>> And what will you do if someone asks you to create an ACL that will
    >>> block every fourth host on a /26 network? i.e. x.x.x.4, x.x.x.68,
    >>> x.x.x.132, x.x.x.196 but permit others?

    >
    > First of all, there are only 3 subnetworks on a /26 network , not 4!
    >
    > x.x.x.0, x.x.x.64, and x.x.x.128


    Don't know what you're talking about or what the relevance is.

    There are four possible values for the final octet in the "host 4"
    IP address of a /26 network. Those are x.x.x.4, x.x.x.68,
    x.x.x.132 and x.x.x.196

    It is the blocking of the "host 4" IP address in all possible /26 netblocks
    that we're after. There isn't any subnetting going on.

    [It took me a bit to catch on. "Every 4th host" isn't very good wording.
    Initially it sounded to me like he wanted the low order two bits of all
    the blocked IP addresses to be identical.]

    >>> Of course you can use four denies at the top and permit the block, but
    >>> for education sake, what if I told you that you can do this with one
    >>> line?
    >>>
    >>> permit ip x.x.x.4 255.255.255.192 is the line you're looking for.

    >
    > I do not see how your line can block every 4 th host and how your line can
    > be any different than
    >
    > "permit ip x.x.x.4 0.0.0.63". Note: ACL uses wildcards.


    Why are you specifying a 4 and then wildcarding it with a 63?

    RTR(config-ext-nacl)#deny ip 1.2.3.4 0.0.0.63 any
    RTR(config-ext-nacl)#^Z
    RTR#show ip access-list test
    Extended IP access list test
    deny ip 1.2.3.0 0.0.0.63 any

    IOS properly ignored the "4".

    How does this succeed in blocking every 4th host?


    Of course we may also ask:

    "Why is he specifying x.x.x and then wildcarding it with a 255.255.255.192?"

    RTR(config)#ip access-list extended test
    RTR(config-ext-nacl)#deny ip 1.2.3.4 255.255.255.192 any
    RTR(config-ext-nacl)#^Z
    RTR#show ip access-list test
    Extended IP access list test
    deny ip 0.0.0.4 255.255.255.192 any

    This ACL entry nicely handles the stated problem.

    I'm using the IOS convention that wildcard masks use set bits to indicate
    wildcard positions and clear bits to indicate positions that must match
    the specified IP address. The PIX convention is, of course, the reverse.

  20. Re: IP 0.0.0.0/0 - 0.0.0.0/32


    wrote in message
    news:G5enUT4+Exyi@eisner.encompasserve.org...
    > In article , "The Dude" > Dude@thedu.de> writes:
    >>
    >> "The Dude" Dude@thedu.de> wrote in message
    >> news:TdQIg.492503$IK3.360274@pd7tw1no...
    >>>
    >>> "Hansang Bae" wrote in message
    >>> news:6jNIg.47239$u05.11356@news-wrt-01.rdc-nyc.rr.com...
    >>>> The Dude wrote:
    >>>> [Cisco wildcards for ACLs]
    >>>>> I do not know about the details, but I find it easy by reversing the
    >>>>> normal subnet mask, i.e.: the wild card for A.B.C.D/ 27
    >>>>> (255.255.255.224) is 0.0.0.31 (255-224)
    >>>>
    >>>> And what will you do if someone asks you to create an ACL that will
    >>>> block every fourth host on a /26 network? i.e. x.x.x.4, x.x.x.68,
    >>>> x.x.x.132, x.x.x.196 but permit others?

    >>
    >> First of all, there are only 3 subnetworks on a /26 network , not 4!
    >>
    >> x.x.x.0, x.x.x.64, and x.x.x.128

    >
    > Don't know what you're talking about or what the relevance is.
    >
    > There are four possible values for the final octet in the "host 4"
    > IP address of a /26 network. Those are x.x.x.4, x.x.x.68,
    > x.x.x.132 and x.x.x.196
    >
    > It is the blocking of the "host 4" IP address in all possible /26
    > netblocks
    > that we're after. There isn't any subnetting going on.
    >
    > [It took me a bit to catch on. "Every 4th host" isn't very good wording.
    > Initially it sounded to me like he wanted the low order two bits of all
    > the blocked IP addresses to be identical.]
    >
    >>>> Of course you can use four denies at the top and permit the block, but
    >>>> for education sake, what if I told you that you can do this with one
    >>>> line?
    >>>>
    >>>> permit ip x.x.x.4 255.255.255.192 is the line you're looking for.

    >>
    >> I do not see how your line can block every 4 th host and how your line
    >> can
    >> be any different than
    >>
    >> "permit ip x.x.x.4 0.0.0.63". Note: ACL uses wildcards.

    >
    > Why are you specifying a 4 and then wildcarding it with a 63?
    >
    > RTR(config-ext-nacl)#deny ip 1.2.3.4 0.0.0.63 any
    > RTR(config-ext-nacl)#^Z
    > RTR#show ip access-list test
    > Extended IP access list test
    > deny ip 1.2.3.0 0.0.0.63 any
    >
    > IOS properly ignored the "4".
    >
    > How does this succeed in blocking every 4th host?
    >
    >
    > Of course we may also ask:
    >
    > "Why is he specifying x.x.x and then wildcarding it with a
    > 255.255.255.192?"
    >
    > RTR(config)#ip access-list extended test
    > RTR(config-ext-nacl)#deny ip 1.2.3.4 255.255.255.192 any
    > RTR(config-ext-nacl)#^Z
    > RTR#show ip access-list test
    > Extended IP access list test
    > deny ip 0.0.0.4 255.255.255.192 any
    >
    > This ACL entry nicely handles the stated problem.
    >
    > I'm using the IOS convention that wildcard masks use set bits to indicate
    > wildcard positions and clear bits to indicate positions that must match
    > the specified IP address. The PIX convention is, of course, the reverse.


    255.255.255.255 is called host mask and specifies the network of one host.
    In the following example it's used to advertise a loopback network:

    (config)# int loopback 0
    (config-if)# ip address 192.168.31.33 255.255.255.255

    The Dude



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