Ping two hosts with netmask /32.

Discussion in 'Cisco' started by wgnoevoi, Aug 19, 2006.

  1. wgnoevoi

    wgnoevoi Guest

    I have so simple network:

    The cisco router connect to catalyst. On catalyst is definition two
    VLAN's. There are two hosts: host_1( and host_2,
    ( is connected to catalyst.
    Hosts are in different VLAN and have network mask /32 ---- it couldn't
    change. Configuration on VLAN's couldn't change too.

    Question: How I can change config on the router interface so host_1 can
    ping host_2? Is it possibility?
    wgnoevoi, Aug 19, 2006
    1. Advertisements

  2. I don't think this would work at all. If your host has a subnet mask of you are telling him that he is the only one in that
    subnet and since he doesn't have a default gateway he can't communicate
    with anyone else... You need to change the subnet mask.

    Note that I'm currently finishing semester 3 of CCNA classes so my
    understanding may not be correct and someone with more experience can
    correct me.
    Danijel Starman, Aug 19, 2006
    1. Advertisements

  3. wgnoevoi

    BernieM Guest

    "/32" is not a valid network mask as it leaves no space to identify the
    network and broadcast address. What operating system has allowed you to
    apply that mask? The smallest network mask is "/30"

    What are the network addresses of the vlans that router has configured? By
    that I mean the actual 'networks' .... not hosts. .

    BernieM, Aug 19, 2006
  4. Correction, there is an RFC that defines /31. It is used especially
    on point-to-point links.
    Walter Roberson, Aug 19, 2006
  5. wgnoevoi

    Wayne Guest

    A loopback interface on a router can have a /32 mask, but that or a
    something similar would be about it.
    To the original poster, is the host in question a router, PC, other??
    Wayne, Aug 19, 2006
  6. wgnoevoi

    wgnoevoi Guest

    It's PC.
    wgnoevoi, Aug 19, 2006
  7. wgnoevoi

    wgnoevoi Guest

    It's PC.
    wgnoevoi, Aug 19, 2006
  8. wgnoevoi

    Merv Guest

    and why can't the netmask be changed ?
    Merv, Aug 19, 2006
  9. On 19.08.2006 16:31 Walter Roberson wrote
    That's theory ... reality tells me

    gw001#sh inter loopback 0
    Loopback0 is up, line protocol is up
    Hardware is Loopback
    Internet address is
    Arnold Nipper, Aug 19, 2006
  10. It's PC.

    And why don't you add host routes (unix slang), i.e.

    host_1: ip route add dev eth0
    host_2: ip route add dev eth0
    Arnold Nipper, Aug 19, 2006
  11. I don't think that will work, because the hosts are in different VLANs.
    Routes like that cause the systems to ARP for each other. But since
    each VLAN is a separate broadcast domain, the ARPs will never reach each

    The only way to communicate between VLANs is via a router. The OP
    didn't mention whether his router is connected to both VLANs -- in fact,
    he didn't say how the router is connected to the switch at all.
    Barry Margolin, Aug 19, 2006
  12. wgnoevoi

    BernieM Guest

    If the router is running proxy-arp the pc's hould be able to communicate.

    BernieM, Aug 19, 2006
  13. Only if the router is connected to both VLANs, and it has appropriate
    routing statements for the /32 addresses.
    Barry Margolin, Aug 20, 2006
  14. wgnoevoi

    BernieM Guest

    yes, and as long as there are no restrictions in place ie. acls' etc. The
    original poster doesn't indicate the extent to which they have access to
    this type of info.

    BernieM, Aug 20, 2006
  15. RFC number please? :)

    Usually in ptp links, ip-addresing scheme took /30 that leaves 4 ip
    addresses 1 for network, 2 for end-point ip, and 1 for broadcast.
    David Sudjiman, Aug 20, 2006
  16. Yes, this loopback addr can use /32 addressing. But it is only for
    redistributing/routing update only. It is a different case.
    David Sudjiman, Aug 20, 2006
  17. RFC 3021 "Using 31-Bit Prefixes on IPv4 Point-to-Point links"
    Walter Roberson, Aug 20, 2006
  18. wgnoevoi

    wgnoevoi Guest

    Thank's everybody.
    It schema wasn't work, i.e. /32 is netmask without host. So for "live"
    interface in CORRECTLY work OS we couldn't config this mask. Because
    this mask contradict exist of interfaces. Another history with
    loopback, i.e. it is emulations networks without host.
    wgnoevoi, Aug 21, 2006
  19. wgnoevoi

    wgnoevoi Guest

    All that I sad before --- folly. Question is unsolvable.
    wgnoevoi, Aug 21, 2006
  20. wgnoevoi

    BernieM Guest

    If the interface is more or less a loopback then you're right .. it's
    unsolvable. It's the same as configuring a "127.x.x.x" address. It doesn't
    matter what mask you use and how many hosts are in the same vlan configured
    this way .... they're never going to talk ... packet are never going to even
    hit the wire.

    BernieM, Aug 21, 2006
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.