Strange network problems - pings to host are fine, pings from host fail

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  • 1. Need some help with multi-netting/IP aliasing
    Here is what I am trying to do.. The router that I have has two ethernet interfaces and I want to give out private dynamic addresses to some machines on a network and also be able to assign static public addresses, either through DHCP reservation or physically assigned, to other machines over the same wire from a single ethernet interface and have both able to reach the internet and each other. So the network would look somthing like this: Public class C address space from upstream | My linux router | 66.119.25.0/24 and 10.0.0.0/16 on the same wire going to the router Is there a way to do this using multi-netting or is there a better way of doing this? Could someone point me in the right direction? Christopher Tyler Total Wireless Communications
  • 2. Very simple WiFi question
    What exactly is the difference between an Access Point and an ordinary, eg PCMCIA, WiFi card? I mean, what is the difference in the way they function? Does the Access Point send out different packets when responding to a client? Is there anywhere online (or at O'Reilly) where this is explained? -- Timothy Murphy e-mail (<80k only): tim /at/ birdsnest.maths.tcd.ie tel: +353-86-2336090, +353-1-2842366 s-mail: School of Mathematics, Trinity College, Dublin 2, Ireland
  • 3. Can't open WMV or JPG from Windows share, but MPG and AVI work fine
    I actually have 2 problems, maybe they are related. I just installed Debian, and samba was included. I messed around with everything and its mostly working. Here is the first problem. I have a computer named Neal. When I double click on it on the Debian box, i get a message sayign I dont have permission. If i type in smb://Neal/Shared then I get a login prompt at it works. I dont understand this, I guess its not picking up the right permissions from windows but im not sure. Second problem: now that I have access to the directory, I can play AVI and MPG files right over the network. But if I try to open a JPG or a WMV i get a message sayign the file doesnt exist. There are also no thumbnails showing, just the icons. If i copy them over the thumbnail instantly loads and it opens fine. I am confused on whether this is a problem with the Windows permissions or the Samba permissions or the Linux permissions. All the windows user accounts are local, there are no domains. Thanks for any info.
  • 4. Routing additional ISDN connection to LAN
    Hi everybody, I've got a Linux server that's already a gateway between an internet connection (eth0) and a LAN (eth1) 192.168.1.x. This server has an ISDN adapter, too, which I use for connecting to a remote computer for administration via ippp0 that has the IP 192.168.2.60. I already added a /sbin/route command to the script ip-ip.local that is: /sbin/route add -host 192.168.2.60 dev ippp0 What I can do is connecting to this computer from my Linux server. What I'd like to do is connecting to this computer from my other computers in eth1 (192.168.1.x). But I just can't manage it. Has anybody got an idea? Best regards, Johann
  • 5. WRT54G router and X (also Netgear)
    Hi, I just made a switch from my old linksys nonwireless DSL/cable router to the WRT54G. I have a linux box set as the DMZ host. I have developed a problem: I run X applications remotely and now it looks like if any X window has no activity for about 10 minutes, the connection to it is dropped (the NAT port mapping expires?). I tried a Netgear router with the same problem. My question is: is this normal behaviour for newer routers? If so, will upgrading the firmware of the WRT54G allow me to change it? Can the firmware of the WRT54G Version 5 be upgraded with 3rd party firmware? Alternatively, can I use the old Linksys router to do the NAT and DHCP and use the new WRT54G to do wireless only? Thanks! Ian

Strange network problems - pings to host are fine, pings from host fail

Postby David Brown » Wed, 03 Dec 2008 02:56:48 GMT

Sorry for the long post - I've tried to outline the symptoms of my 
problem, and what I've tried to fix it.


I'm having some networking problems with a PC running an old version of 
Red Hat (kernel 2.2).  The PC came with a machine we have bought 
second-hand - as far as I know, everything was working before the 
machine was moved to our company.

To keep things simple, we have the Red Hat machine connected to a 
Windows XP machine that came with it, with only a simple switch in 
between.  Each machine is set up with a fixed IP address on the same 
network.

 From the XP machine, I can ping the Red Hat machine reliably and 
quickly.  From the Red Hat machine, pings to the XP machine /generally/ 
fail - typically there are about 80%-90% failures.  Those pings that 
don't fail, are fast (reply time about 1 ms).  On the XP machine, it's 
easy to see the packet counters showing packets in and replies out.  On 
the Red Hat machine, ifconfig shows similar packet rx and tx counts, and 
zero error counts.

arping to the XP machine from the Red Hat machine is reliable and fast.

When we try a browser on the XP machine and address the web server on 
the Red Hat host, there is generally a long pause (perhaps minutes), 
then suddenly the page appears.

We have tried using another Linux box in place of the original XP 
machine, with the same results from the Red Hat system.

We have tried replacing the cables and switch, with no effect - given 
that arpings are working perfectly it's hard to see how it could be a 
hardware problem.

I'm not very familiar with Red Hat or a 2.2 kernel (my experience is 
mostly with Debian and related distros, and with 2.4 and 2.6 kernels). 
But "ipchains -L" shows no firewalling (everything accepted), "ifconfig" 
and "route -n" have the expected setup, and I could not stop anything 
unexpected with "sysctrl".

One of my colleagues will try a different network card this evening.


Any ideas or tips would be much appreciated.  We've tried pretty much 
every sensible idea we can think of, so I'm ready to listen to any crazy 
or unlikely tricks.

mvh.,

David

Re: Strange network problems - pings to host are fine, pings from host fail

Postby Balwinder S Dheeman » Wed, 03 Dec 2008 03:44:45 GMT



I think, you need to check DNS settings/entries on both of your XP as 
well as RH machines; better automate all these and, or other such things 
with the help of a DHCP server.

Moreover, try syncing your C:\WINDOWS\system32\drivers\etc\hosts file on 
XP machine with the one /etc/hosts on you RH machine.

Or, better run a DNS server having zones for local/private network/segments.

Hope that helps,
-- 
Dr Balwinder S "bsd" Dheeman          Registered Linux User: #229709
Anu'z Linux@HOME (Unix Shoppe)        Machines: #168573, 170593, 259192
Chandigarh, UT, 160062, India         Gentoo, Fedora, Debian/FreeBSD/XP
Home:  http://www.**--****.com/ ~bsd/  Visit:  http://www.**--****.com/ 

Re: Strange network problems - pings to host are fine, pings from host fail

Postby Robert Harris » Wed, 03 Dec 2008 03:52:36 GMT


You may well have a hardware problem in your network. Try connecting 
your Red Hat machine directly to your XP machine with a crossover cable 
and try pinging again.

Robert

Re: Strange network problems - pings to host are fine, pings from host fail

Postby Tauno Voipio » Wed, 03 Dec 2008 04:17:29 GMT



Have you tried ping -n ?

-- 

Tauno Voipio
tauno voipio (at) iki fi


Re: Strange network problems - pings to host are fine, pings from host fail

Postby David Brown » Wed, 03 Dec 2008 05:38:38 GMT

alwinder S Dheeman wrote:

It's not a DNS problem - I'm pinging by IP address. I'm trying to keep
things as simple as possible until I know what's going wrong.

We have a DNS server on the router to which these machines will be
attached, once we've got this problem figured out. And yes, I'll be
using the hosts files on both machines to make sure the naming is right.

Thanks for the ideas anyway.

mvh.,

David

Re: Strange network problems - pings to host are fine, pings from host fail

Postby David Brown » Wed, 03 Dec 2008 05:43:39 GMT

obert Harris wrote:

We thought of that, but I couldn't find a crossover cable at the office
(we haven't needed crossover cables for a decade or so). We have tried
connecting using only a modern switch, and also using an old 10 MBit
hub, as well as connecting them on the LAN side of a small router (a
LinkSys WRT54GL running openwrt). There were absolutely no differences,
so I don't think the problem can be there.

If there is a hardware problem, it must lie with the network card on the
Red Hat machine, as everything else has been tested (different cables,
different target machines, etc.). It's conceivable that the card has
come lose while transporting the machine to our offices, I suppose.
I'll know a little more in the morning (after my colleague has tried a
different network card).

Re: Strange network problems - pings to host are fine, pings from host fail

Postby David Brown » Wed, 03 Dec 2008 06:15:42 GMT





I'm already pinging by ip address, so "ping -n" should not make a 
difference.  Or is it the case that with this setup (either Red Hat 
specific, or kernel 2.2, or older versions of ping and the resolver 
libraries), that ping without the "-n" will try to do a reverse DNS 
lookup to find a name for the ip address I'm pinging?  I must admit that 
I haven't worried too much about DNS so far, since I am sticking to IP 
addresses first.  The DNS server specified on the Red Hat machine does 
not exist in our network (it is a local address on the original user's 
network), so perhaps ping is{*filter*} when trying to resolve a name for 
the address.  A similar thing may be happening with the web server 
accessed by the client machine.  This is not a problem I've seen before 
(I've seen other DNS issues, and also set up nodes and networks with no 
DNS at all), but it may just be the problem.

I'll try out some fixes first thing in the morning when I'm back at the 
office (firstly by putting the ip addresses I'm pinging in the hosts file).

Thanks for the hint!

mvh.,

David

Re: Strange network problems - pings to host are fine, pings from host fail

Postby Allen McIntosh » Wed, 03 Dec 2008 10:08:30 GMT





By default, ping tries reverse DNS on the source IP address of the 
packet it gets back.

Re: Strange network problems - pings to host are fine, pings from host fail

Postby David Brown » Wed, 03 Dec 2008 17:06:06 GMT







That was the problem.  A couple of lines in the hosts file (and correct 
DNS setup once the system was connected to the rest of the network), and 
everything worked perfectly.

Many thanks to those who replied on this thread - I've learned something 
new, and fixed our problem.

mvh.,

David



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3.pinging to neighbour host problem

Hello,
 I am running ethereal on linux on pcs with pc1 with ip
address=192.18.1.250 and pc2 with ip=192.168.1.10. I am pinging from
pc1 to p2 but sometimes packet goes normal way and sometimes i think
frame corrupted. Following my capture znalysis ON PC2. First Frame is
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 eth1      Link encap:Ethernet  HWaddr 00:08:A1:43:61:F5
          inet addr:192.168.1.10  Bcast:192.168.1.255
Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:33 errors:0 dropped:0 overruns:0 frame:0
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          RX bytes:3494 (3.4 Kb)  TX bytes:2246 (2.1 Kb)
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No.     Time        Source                Destination
Protocol Info
      1 0.000000    40:00:40:01:b6:54     45:00:00:54:00:00     0xc0a8
 Ethernet II

Frame 1 (98 bytes on wire, 98 bytes captured)
    Arrival Time: May 20, 2005 15:57:13.599959000
    Time delta from previous packet: 0.000000000 seconds
    Time since reference or first frame: 0.000000000 seconds
    Frame Number: 1
    Packet Length: 98 bytes
    Capture Length: 98 bytes
    Protocols in frame: eth:data
Ethernet II, Src: 40:00:40:01:b6:54, Dst: 45:00:00:54:00:00
    Destination: 45:00:00:54:00:00 (45:00:00:54:00:00)
    Source: 40:00:40:01:b6:54 (40:00:40:01:b6:54)
    Type: Unknown (0xc0a8)
Data (84 bytes)

0000  45 00 00 54 00 00 40 00 40 01 b6 54 c0 a8 01 fa
E..T..@.@..T....
0010  c0 a8 01 0a 08 00 df 9d 52 0e 00 01 22 bf 8d 42
........R..."..B
0020  1e 4e 0d 00 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13
.N..............
0030  14 15 16 17 18 19 1a 1b 1c 1d 1e 1f 20 21 22 23   ............
!"#
0040  24 25 26 27 28 29 2a 2b 2c 2d 2e 2f 30 31 32 33
$%&'()*+,-./0123
0050  34 35 36 37 00 00 00 00 00 00 00 00 00 00 00 00
4567............
0060  00 00                                             ..

Frame 5 (98 bytes on wire, 98 bytes captured)
    Arrival Time: May 20, 2005 16:12:42.872068000
    Time delta from previous packet: 177.629913000 seconds
    Time since reference or first frame: 182.659884000 seconds
    Frame Number: 5
    Packet Length: 98 bytes
    Capture Length: 98 bytes
    Protocols in frame: eth:ip:icmp:data
Ethernet II, Src: 00:08:a1:43:62:91, Dst: 00:08:a1:43:61:f5
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    Type: IP (0x0800)
Internet Protocol, Src Addr: 192.168.1.250 (192.168.1.250), Dst Addr:
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    Version: 4
    Header length: 20 bytes
    Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
        0000 00.. = Differentiated Services Codepoint: Default (0x00)
        .... ..0. = ECN-Capable Transport (ECT): 0
        .... ...0 = ECN-CE: 0
    Total Length: 84
    Identification: 0x0000 (0)
    Flags: 0x04 (Don't Fragment)
        0... = Reserved bit: Not set
        .1.. = Don't fragment: Set
        ..0. = More fragments: Not set
    Fragment offset: 0
    Time to live: 64
    Protocol: ICMP (0x01)
    Header checksum: 0xb654 (correct)
    Source: 192.168.1.250 (192.168.1.250)
    Destination: 192.168.1.10 (192.168.1.10)
Internet Control Message Protocol
    Type: 8 (Echo (ping) request)
    Code: 0
    Checksum: 0xdf9d (correct)
    Identifier: 0x520e
    Sequence number: 0x0001
    Data (56 bytes)

0000  00 08 a1 43 61 f5 00 08 a1 43 62 91 08 00 45 00
...Ca....Cb...E.
0010  00 54 00 00 40 00 40 01 b6 54 c0 a8 01 fa c0 a8
.T..@.@..T......
0020  01 0a 08 00 df 9d 52 0e 00 01 22 bf 8d 42 1e 4e
......R..."..B.N
0030  0d 00 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15
................
0040  16 17 18 19 1a 1b 1c 1d 1e 1f 20 21 22 23 24 25   ..........
!"#$%
0050  26 27 28 29 2a 2b 2c 2d 2e 2f 30 31 32 33 34 35
&'()*+,-./012345
0060  36 37                                             67

4.arp problem in pinging host

[Removed comp.protocols.tcp-ip since it isn't relevant]

I guess I should have asked for ifconfig -a in the same post - 
newsreader won't let me go back and look at original.  Anyway
> Routing table for hostA
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref    Use
> Iface
> 192.168.1.0     0.0.0.0         255.255.255.0   U     0      0        0
> eth0
> 172.16.1.0      192.168.1.1     255.255.255.0   UG    0      0        0
> eth0
OK but redundant, since it is covered by the default route.
> 0.0.0.0         192.168.1.1     0.0.0.0         UG    0      0        0
> eth0
So eth0 has an IP addr of 192.168.1.x where x != 1, and is connected by 
a crossover cable to eth1 on R1.  eth1 on R1 has address 192.168.1.1. 
OK so far?

> Routing table for R1
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref    Use
> Iface
> 192.168.1.0     0.0.0.0         255.255.255.0   U     0      0        0
> eth1
> 172.16.1.0      0.0.0.0	  255.255.255.0   UG    0      0        0 eth0
Redundant.
> 10.0.0.0        0.0.0.0         255.0.0.0       U     0      0        0
> eth0
> 0.0.0.0         10.1.1.100      0.0.0.0         UG    0      0        0
> eth0
eth1 had address 192.168.1.1 and is connected to A.
eth0 has address 10.1.1.1 and is connected to R2.  More on this later.
> 
> I have also crosscable connection of R1 to another R2  with routing
> table
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref    Use
> Iface
> 192.168.1.0     0.0.0.0         255.255.255.0   U     0      0        0
> eth0
> 172.16.1.0      0.0.0.0	  255.255.255.0   UG    0      0        0 eth1
> 10.0.0.0        0.0.0.0         255.0.0.0       U     0      0        0
> eth0
> 0.0.0.0         10.1.1.1        0.0.0.0         UG    0      0        0
> eth0
eth0 has address 10.1.1.100 and is connected to R1 via crossover cable? 
  I see several things wrong with this.  First, R1 and R2 send default 
traffic to each other.  Second, it would be more usual to use a netmask 
of 255.255.255.0 for the 10.1.1.0 network.  Third, I don't understand 
how the 192.168.1 entry got here or what it is supposed to be doing. 
(There are two wildly different networks assigned to the same interface 
with no gateway on either entry.)  The 172.16.1.0 entry looks funny too. 
  What is the address of eth1 supposed to be?


I think you need to sit down with a piece of paper and draw your 
network.  For each network segment (each crossover cable is one) write 
in the interface name, the addresses of each interface, the network 
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the routing tables and addresses (output of ifconfig -a or equivalent) 
match the diagram.

5.Can ping on both ip and host name but nbtstat -a gets "host not found"

We have 2 servers with NT4 that we are trying to install Symantec antivirus 8,1 with another server as parent server and it fails because the server can not be found
Doing a Ping from the server that we are trying to install on works fine on both IPadress and host name but trying to do a nbtstat -a ends up with a "host not found !!
All IP-configurations are correct on both servers and is the same as all our servers where we had no problems doing the SAV installation
I dont have a clue what causes this and i wonder if someone else has an idea

//Thomas

6. Pinging Host Names as opposed to pinging FQDNs

7. ping hostname failed while ping IP_Address working Options

8. ping from vxsim to host linux machine



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