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3400 Views 14 Replies Latest reply: Oct 1, 2012 11:31 PM by Nadeem RSS

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Special IP addresses

Sep 19, 2012 2:25 AM

Nadeem 13 posts since
Sep 19, 2012

Can anyone explain to me what is the main purpose of IPs written bellow and how should I understand it:

 

1. 255.255.0.0/32

2. 255.255.0.0/0

3. 255.255.255.255/0

4. 255.255.255.255/32

5. 0.0.0.0/0

6. 0.0.0.0/32

7. 192.168.34.5/0

8. 192.168.34.5/32

9. 0.0.0.0/24

10. 255.255.255.255/24

  • lp4nb 520 posts since
    Jun 27, 2009
    Currently Being Moderated
    2. Sep 19, 2012 7:03 AM (in response to Nadeem)
    Re: Special IP addresses

    All entries with /0  will match everything.

    All entries with /32 will match exact part  a.a.a.a/32 - will only match a.a.a.a and nothing else.

    the entry with /24 must have first 3 octet as 0, and fourth could be anything.

    ----------

  • lp4nb 520 posts since
    Jun 27, 2009
    Currently Being Moderated
    4. Sep 19, 2012 8:18 AM (in response to Nadeem)
    Re: Special IP addresses

    I think you're wrong: /0 will match only one IP address and /32 will be used for 'any'.

    ?? how

    But what is the meaning and purpose of those addresses? I mean why should you use one those addresses, if you have normal private IPs such as those in A,B,C classes or the public ones? It's special address, but I dont know for what it should be used, specialy with those masks, and how it's processed by IOS?

     

    not all the listed one are special IP addresses.

    0.0.0.0/0 -- means all ip address.

    0.0.0.0/32 is host ip add, kind of a broadcast, RFC 5735, 1700 may help.

     

    255.255.255.255/32 is broadcast address on the local to a network, as router won't forward it.

    I don't see any other special route here.

  • cadetalain 2,642 posts since
    Sep 18, 2008
    Currently Being Moderated
    6. Oct 1, 2012 5:32 AM (in response to Nadeem)
    Re: Special IP addresses

    Hi,

     

    ip route any 180.96.40.112  is not a valid syntax

    default route   is the catch all route

    default-gateway only used if not routing

    default-network is for EIGRP: you say hey guys if you want to go to a destination you don't know about go the same way you would go for this network.

     

    Regards.

     

    Alain

  • cadetalain 2,642 posts since
    Sep 18, 2008
    Currently Being Moderated
    8. Oct 1, 2012 7:20 AM (in response to Nadeem)
    Re: Special IP addresses

    Hi,

    deny ip host 0.0.0.0 any  --> denies src IP= 0.0.0.0 to any dst IP

    deny ip host 255.255.255.255 any ---> denies src IP= 255.255.255.255 to any dst IP

    deny ip 0.0.0.0 0.255.255.255 any --->  denies any src IP to any dst IP

    deny ip 166.55.73.138 255.255.255.255 any ---> same as above

     

    Regards.

     

    Alain

  • Luke Savage 41 posts since
    Feb 4, 2011
    Currently Being Moderated
    10. Oct 1, 2012 1:01 PM (in response to Nadeem)
    Re: Special IP addresses

    Hello Nadeem,

     

    Host 0.0.0.0 would deny the individual host with IP address 0.0.0.0 however the 0.x.x.x range is not generally assigned to devices(see comment below).
    Host 255.255.255.255 would only deny indivudal address 255.255.255.255 and this is a broadcast address. So having the entry in the destination field of the ACL would block all IP broadcasts.

    Network 0.0.0.0/8 - Current network (only valid as source address) RFC 1700. I'm not sure what effect this would have on an ACL.

    166.55.73.138 255.255.255.255 is the same as "any any" or "0.0.0.0 255.255.255.255" and would deny all traffic.

     

    Remember, in extended ACL's you must always specify source and destination addresses.

     

    Luke

  • Luke Savage 41 posts since
    Feb 4, 2011
    Currently Being Moderated
    12. Oct 1, 2012 6:40 PM (in response to Nadeem)
    Re: Special IP addresses

    1. I did a bit more reading and it's not quite the same. Addresses on the 0.0.0.0/8 network appear to refer to devices on "this network". "This network" being whatever network the machine is attached to. This would be used if the device cannot obtain a DHCP address and has been replaced by APIPA in Windows machines.

     

    "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 ([RFC1122], Section

    3.2.1.3)." - http://tools.ietf.org/html/rfc5735

     

    2. Yes, when configuring ACL's 0.0.0.0 in the wildcard section is the same as specifying host and 255.255.255.255 is the same as saying any address.


    Example:
    All of the below ACL commands would result in all IP traffic being permitted.

    access-list 111 permit IP any any

    access-list 111 permit IP 0.0.0.0 255.255.255.255 0.0.0.0 255.255.255.255

    access-list 111 permit IP 0.0.0.0 255.255.255.255 any
    access-list 111 permit IP any 0.0.0.0 255.255.255.255
    access-list 111 permit IP 192.168.2.5 255.255.255.255 52.62.1.23 255.255.255.255 < not much point in this line but you get the idea.

     

    Luke

  • cadetalain 2,642 posts since
    Sep 18, 2008
    Currently Being Moderated
    13. Oct 1, 2012 11:25 PM (in response to Luke Savage)
    Re: Special IP addresses

    Hi,

    1) windows APIPA aka IPv4 link-local aka 169.254.x.x/16 is not 0.0.0.0

       0.0.0.0 is unspecified address used when a client without any IP first tries to contact  a DHCP server

    2) in wildcard mask: a zero is a "care bit" and a 1 is a "don't care" bit

        so 0.0.0.0 means match all bits so= host and 255.255.255.255 means don't care

       to match any bits = any

      so you could put any ip address with a wildcard mask of all 1s it still would mean any, the IP address is just a placeholder.

     

    Regards.

     

    Alain

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