Destination Host Unreachable - Networking

This is a discussion on Destination Host Unreachable - Networking ; On Wed, 5 Dec 2007, in the Usenet newsgroup comp.os.linux.networking, in article , Phi wrote: NOTE: Posting from groups.google.com (or some web-forums) dramatically reduces the chance of your post being seen. Find a real news server. >My understanding of route ...

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Thread: Destination Host Unreachable

  1. Re: Destination Host Unreachable

    On Wed, 5 Dec 2007, in the Usenet newsgroup comp.os.linux.networking, in
    article ,
    Phi wrote:

    NOTE: Posting from groups.google.com (or some web-forums) dramatically
    reduces the chance of your post being seen. Find a real news server.

    >My understanding of route -v is that it responds using symbolic names
    >for the hosts it finds.


    Have you looked at the man page? It's fairly well explained there.

    [compton ~]$ whatis route
    route (8) - show / manipulate the IP routing table
    [compton ~]$

    >So, it shows link-local as a host. Since the gateway has no symbolic
    >name, it shows as a blank.


    No on both counts. Let's recopy your display here:

    ]route -v
    ]Kernel IP routing table
    ]Destination Gateway Genmask Flags Metric Ref Use Iface
    ]192.168.1.0 * 255.255.255.0 U 0 0 0 eth0
    ]link-local * 255.255.0.0 U 0 0 0 eth0
    ]default 0.0.0.0 UG 0 0 0 eth0

    The names 'link-local' and 'default' translate to a network named
    'link-local' (169.254.0.0/16), and a route to use when no other route
    will take your packets where they need to go. The 'link-local' is an
    Apple invention copied by windoze, and used when a computer can't find
    a DHCP server to get a "real" address. It gets included in some Linux
    distributions because of the abundance of mis-configured windoze systems
    often found on home networks. It's a "don't bother fixing the problem,
    just make it work and I don't care about security" solution from windoze.
    You can disable this "feature" by including a line in the file
    '/etc/sysconfig/network' that says "NOZEROCONF=yes".

    The 'default' route is that route used when no other listed route will
    take you where you want to go. This is _NORMALLY_ considered to be the
    route to "the world". The lack of a name or the '*' character indicates
    that '/sbin/route' is finding some name for that gateway device, but is
    unable to display the name - generally a screwed up nameserver, or bad
    entry in the /etc/hosts file.

    Note that none of the routes you show are routes to individual hosts.
    These would be identified by a 'Genmask' of '255.255.255.255' and an
    'H' flag. I'm not exactly sure where you got this routing table, as
    it has several problems. This _should_ look like this:

    Kernel IP routing table
    Destination Gateway Genmask Flags Metric Ref Use Iface
    192.168.1.0 * 255.255.255.0 U 0 0 0 eth0
    link-local * 255.255.0.0 U 0 0 0 eth0
    127.0.0.0 * 255.0.0.0 U 0 0 0 lo
    default 192.168.1.1 0.0.0.0 UG 0 0 0 eth0

    Finally, when the 'route' command is unable to determine a name for
    a host or network, it puts in the numeric address. You could use the
    -n option to get this behavior by default.

    >I also posted netstat -rn. That shows the IP addresses for the
    >connections. It shows 192.168.1.1 for the gateway address.


    [compton ~]$ whatis netstat
    netstat (8) - Display network connections, routing tables,
    interface statistics, masquerade connections and netlink messages
    [compton ~]$

    If you looked at the man page for 'netstat' (actual syntax 'man netstat')
    you would find

    -r, --route
    With the -r, --route option, you get the kernel routing tables in
    the same format as route -e use. netstat -er will use the output
    format of route. Please see route(8) for details.

    -n, --numeric
    shows numerical addresses instead of trying to determine symbolic
    host, port or user names.

    so the data shown by '/bin/netstat -rn' should be essentially the same
    as shown by '/sbin/route -n'

    Old guy

  2. Re: Destination Host Unreachable

    On Wed, 5 Dec 2007, in the Usenet newsgroup comp.os.linux.networking, in
    article <02b637cb-ed2f-45a6-8968-1240ebef84ea@a35g2000prf.googlegroups.com>,
    Phi wrote:

    NOTE: Posting from groups.google.com (or some web-forums) dramatically
    reduces the chance of your post being seen. Find a real news server.

    >The gateway is 192.168.1.1
    >It did not show in route -v, because there is no symbolic name for it.


    Not true, but you could fix that by entering the hostname and address
    in /etc/hosts. What does 'route -vn' show?

    >It does show correctly for netstat -rn.
    >DNS was entered as shown in resolv
    >======== grep -v '^#' /etc/resolv.conf ==========
    >nameserver 29.25.5.60
    >nameserver 29.25.5.61
    >Using nameserves outside the local network is normal.


    Generally, it's frowned upon to try to use nameservers other than your
    own, or those of your ISP. External users asking a name server to resolve
    names/addresses it's not authoratative for is considered abuse by some,
    and I've know people to configure their nameserver to respond with an
    NXDOMAIN rather than the more correct REFUSED result code.

    >I may set up the linux system to do dns for itself for nodes on the
    >local network.


    The addresses you show certainly won't work from here - my routers tell
    me that no one admits to knowing how to send packets to that military
    network. As you are posting from

    NNTP-Posting-Host: 70.60.226.186

    maybe you'd have better luck using one of the name servers associated
    with Road Runner Commercial (24.30.200.19, 24.30.201.19, or 65.24.0.172),
    or one associated with the techtriad.com (there are five to choose from).

    Old guy

  3. Re: Destination Host Unreachable

    ibuprofin@painkiller.example.tld (Moe Trin) writes:

    >On Tue, 04 Dec 2007, in the Usenet newsgroup comp.os.linux.networking, in
    >article <47556a3f$0$29252$ba620e4c@news.skynet.be>, goarilla wrote:


    >>david wrote:


    >>> Phi rearranged some electrons to say:


    >>> route -v
    >>> Kernel IP routing table
    >>> Destination Gateway Genmask Flags Metric Ref Use Iface
    >>> 192.168.1.0 * 255.255.255.0 U 0 0 0 eth0
    >>> link-local * 255.255.0.0 U 0 0 0 eth0
    >>> default 0.0.0.0 UG 0 0 0 eth0
    >>>

    >> Something seems wrong with the gateway on your default route.. it
    >> shouldn't be blank, should it?


    Nope, it is fine, assuming that any of the machines that he wants to reach
    are on his local ethernet so the arp table can get to them.
    If that assumption is not true, then yes, he needs a gateway host which
    knows how to send on the packets.

    >>
    >>he's right do this (as root):
    >>/sbin/route del default
    >>/sbin/route add default gw 192.168.1.1 netmask 255.255.255.0

    > ^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^


    Why in the world would you want a netmask other than 0.0.0.0 on the
    default. Yours says that the ONLY addresses to be sent to the gateway have
    the IP addresses of 0.0.0.x where x is any 8 bit number. I do not think
    that is what you want. YOu want
    netmask 0.0.0.0 but then that is the default with default.


    >


    >Ummmm.... you realy need to re-read that man page, usless this is one
    >hell of a typ0. The "default" route is defined in the terms of a
    >programming choice. If the other choices don't work to get you where you
    >are going, send it here _by default_ (which in the Linux tools sense
    >really means this is the route to the entire world). Last time I checked,
    >the world doesn't exist in a 255.255.255.0 mask, and the correct mask is
    >the default for a default route - which is to say 0.0.0.0.


    Are there any valid IP addresses of the form 0.0.0.x?


    > Old guy


  4. Re: Destination Host Unreachable

    On Fri, 07 Dec 2007 04:58:17 +0000, Unruh rearranged some electrons to
    say:

    > ibuprofin@painkiller.example.tld (Moe Trin) writes:
    >
    >>On Tue, 04 Dec 2007, in the Usenet newsgroup comp.os.linux.networking,
    >>in article <47556a3f$0$29252$ba620e4c@news.skynet.be>, goarilla wrote:

    >
    >>>david wrote:

    >
    >>>> Phi rearranged some electrons to say:

    >
    >>>> route -v
    >>>> Kernel IP routing table
    >>>> Destination Gateway Genmask Flags Metric Ref Use
    >>>> Iface 192.168.1.0 * 255.255.255.0 U 0 0
    >>>> 0 eth0 link-local * 255.255.0.0 U 0 0
    >>>> 0 eth0 default 0.0.0.0 UG 0 0
    >>>> 0 eth0
    >>>>
    >>> Something seems wrong with the gateway on your default route.. it
    >>> shouldn't be blank, should it?

    >
    > Nope, it is fine, assuming that any of the machines that he wants to
    > reach are on his local ethernet so the arp table can get to them. If
    > that assumption is not true, then yes, he needs a gateway host which
    > knows how to send on the packets.


    The OP said he could not ping his router, nor access the outside world:

    "When I boot FC8, I have no network or internet access. I can not even
    reach the gateway router."


  5. Re: Destination Host Unreachable

    On Fri, 07 Dec 2007, in the Usenet newsgroup comp.os.linux.networking, in
    article , Unruh wrote:

    >(Moe Trin) writes:


    >> goarilla wrote:


    >>> david wrote:


    >>>> Phi rearranged some electrons to say:


    >>>> route -v
    >>>> Kernel IP routing table
    >>>> Destination Gateway Genmask Flags Metric Ref Use Iface
    >>>> 192.168.1.0 * 255.255.255.0 U 0 0 0 eth0
    >>>> link-local * 255.255.0.0 U 0 0 0 eth0
    >>>> default 0.0.0.0 UG 0 0 0 eth0
    >>>>
    >>> Something seems wrong with the gateway on your default route.. it
    >>> shouldn't be blank, should it?


    >Nope, it is fine, assuming that any of the machines that he wants to
    >reach are on his local ethernet so the arp table can get to them.


    Bill, please read the original posts before making wild assumptions.
    First, notice that the two other entries on this output show a '*' for
    the gateway, and the default route does not. As the O/P is not using
    the -n option to /sbin/route, the command will try to display the
    hostname if it can determine it. IT IS DOING SO HERE, except that the
    name it's trying to display is screwed up - either a bunch of leading
    spaces in the name, or non-ASCII characters. IF THERE WAS NO GATEWAY,
    THE COMMAND WOULD DISPLAY A '*' IN THAT FIELD. A further clue is
    that the O/P also included the output of '/bin/netstat -nr' which,
    because of the -n option, is displaying the dotted quad IP address.

    >>>he's right do this (as root):
    >>>/sbin/route del default
    >>>/sbin/route add default gw 192.168.1.1 netmask 255.255.255.0

    > ^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^
    >Why in the world would you want a netmask other than 0.0.0.0 on the
    >default.


    If you read the rest of the thread, this poster admitted his mistake.

    >Are there any valid IP addresses of the form 0.0.0.x?


    Yes. See RFC1122 section 3.2.1.3 which discusses RFC0791 section 3.2.
    Briefly, 0,0 (network address 0 and within that network, host address
    0) means "this" host - where I don't know my address. It's generally
    seen in the start of DHCP/BOOTP conversations. The 0, host-id address
    (network part zeroed, host part specific to some host) is also allowed.
    However, routers should not forward these packets except in specific
    special circumstances (one example being a DHCP relay agent).

    Old guy

  6. Re: Destination Host Unreachable

    Thanks to all who tried to help me with this problem. Unfortunately,
    nothing suggested worked.

    I reinstalled FC8 in the 32-bit version. That didn't work either.

    I reinstalled FC7 and that worked without effort.

    I guess I'll just wait for FC9.


  7. Re: Destination Host Unreachable

    I had a very similar problem. I ran across this thread and tried everything in here but nothing helped.
    Then i started doing some fine grained debugging.
    I started noting that at shutdown irqbalance daemon kept failing.
    After reading about the irqbalance daemon, i realized its something that i do not need because i am running a single processor.
    Once I turned off the irqbalance daemon from startup and walah the magic happened. My network suddenly started working.
    I noticed in ifconfig of eth0 on FC5 on same box was giving me interrup of 21 where as in FC8 on same box i was getting interrup of 18 how can that be possible if i am using the same hardware.
    Once i turned off irqbalance my interrupt was back to 21 in fc8.
    I noticed the person who posted this problem was also using a single xenon processor. I suggest that he do the same and I bet it should work.

    Best regards
    FCGURU

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