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Second ethernet card on different subnet causing Neighbour table overflow messages

Second ethernet card on different subnet causing Neighbour table overflow messages

Post by Raid » Tue, 24 Sep 2002 11:04:55



Hello,

I just installed a separate NIC on my computer, and I am now receiving the
following errors:
Sep 22 18:04:21 mail kernel: NET: 9 messages suppressed.
Sep 22 18:04:21 mail kernel: Neighbour table overflow.
Sep 22 18:04:23 mail last message repeated 9 times
Sep 22 18:04:27 mail kernel: NET: 15 messages suppressed.
Sep 22 18:04:27 mail kernel: Neighbour table overflow.

I never had any such errors prior to the installation of the second NIC on
eth1.  I wanted this computer to be directly accessible by two different
CLASS C subnets.  This server receives quite a bit of traffic from the
64.61.132 subnet via eth1, and sends this traffic out over the 64.61.133
subnet over via eth0.  Rather than having traffic from 64.61.132 go through
a separate gateway to the 64.61.133 network (and then on to this machine),
I wanted the machine itself to route the traffic and send the mail at the
same time.

I have read through the newsgroups, and it seems that there are two major
possibilities for the errors.  First, the lo device is not configured (which
it looks like it is, as seen below.)  This doesn't appear to be the problem.

Second, and more likely, there is an issue with the machine thinking that
various destinations are "local neighbors" on the same subnet.  The above
error messages happen when the 64.61.132 network is sending a lot of traffic
to this machine on its eth1 interface, which in turn emails via the 64.61.133
network over its eth0 interface.

One other twist is that both subnets are being processed through the same
switch, and this is what I'm guessing is making the situation complex.

The 64.61.132 network has its own separate gateway to the internet, as does
the 64.61.133 network.  Since both networks operate (independently?) on the
Level 2 switch, I would assume that this wouldn't be an issue.  But, just
in case the presence of both ethernet frames on the same switch is the
cause for all of the ARP confusion, I wanted to mention it.

So, it basically looks like:

                     *INTERNET*
                          |
    /--------------------------------------------\
    |                                            |
   GW to  (64.61.132.233)                       GW to  (64.61.133.26)
   Internet                                     Internet
    |                                            |
|---------|  eth1*------------------*eth0    |---------|
|64.61.132| ---> |64.61.132.236 eth0| --->   |64.61.133| (mail is sent
| network |      |64.61.133.26 eth1 | (mail) | network |  from 64.61.133
|---------|      *--(mail server)---*        |---------|  network)
(mail originates
 in 64.61.132 network)

ifconfig shows:
eth0      Link encap:Ethernet  HWaddr 00:E0:81:21:DF:7E  
          inet addr:64.61.133.26  Bcast:64.61.133.31  Mask:255.255.255.248
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:377123 errors:0 dropped:0 overruns:0 frame:0
          TX packets:251573 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100
          RX bytes:81228349 (77.4 Mb)  TX bytes:61257079 (58.4 Mb)
          Interrupt:11 Base address:0x9000

eth1      Link encap:Ethernet  HWaddr 00:E0:81:21:DF:7F  
          inet addr:64.61.132.236  Bcast:64.61.132.239  Mask:255.255.255.248
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:24222 errors:0 dropped:0 overruns:0 frame:0
          TX packets:137458 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100
          RX bytes:1726713 (1.6 Mb)  TX bytes:18298917 (17.4 Mb)
          Interrupt:10 Base address:0xb000

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:186847 errors:0 dropped:0 overruns:0 frame:0
          TX packets:186847 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:31903076 (30.4 Mb)  TX bytes:31903076 (30.4 Mb)

Here is what route -n shows:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
64.61.133.24    0.0.0.0         255.255.255.248 U     0      0        0 eth0
64.61.132.232   0.0.0.0         255.255.255.248 U     0      0        0 eth1
127.0.0.0       0.0.0.0         255.0.0.0       U     0      0        0 lo
0.0.0.0         64.61.133.26    0.0.0.0         UG    0      0        0 eth0

/etc/sysconfig/network:
NETWORKING=yes
HOSTNAME=mail.testing.net
GATEWAY=64.61.133.26
GATEWAYDEV=eth0

This is a redhat 7.3 machine, using kernel 2.4.18-3.

Does anyone have any suggestions on how to resolve these error messages?
The network operation does seem to work correctly, but I would like to get
rid of the constant thrashing of the ARP table so I can avoid these
messages (and also get rid of the fact that it thinks it needs to keep
adding all of the mail recipients to its "local neighbors" table).

Thank you in advance for any help or advice!

-Raiden

 
 
 
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Second ethernet card on different subnet causing Neighbour table overflow messages

Post by nick haddo » Tue, 24 Sep 2002 18:10:10



> Hello,

> I just installed a separate NIC on my computer, and I am now receiving the
> following errors:
> Sep 22 18:04:21 mail kernel: NET: 9 messages suppressed.
> Sep 22 18:04:21 mail kernel: Neighbour table overflow.
> Sep 22 18:04:23 mail last message repeated 9 times
> Sep 22 18:04:27 mail kernel: NET: 15 messages suppressed.
> Sep 22 18:04:27 mail kernel: Neighbour table overflow.

> I never had any such errors prior to the installation of the second NIC on
> eth1.  I wanted this computer to be directly accessible by two different
> CLASS C subnets.  This server receives quite a bit of traffic from the
> 64.61.132 subnet via eth1, and sends this traffic out over the 64.61.133
> subnet over via eth0.  Rather than having traffic from 64.61.132 go through
> a separate gateway to the 64.61.133 network (and then on to this machine),
> I wanted the machine itself to route the traffic and send the mail at the
> same time.

> I have read through the newsgroups, and it seems that there are two major
> possibilities for the errors.  First, the lo device is not configured (which
> it looks like it is, as seen below.)  This doesn't appear to be the problem.

> Second, and more likely, there is an issue with the machine thinking that
> various destinations are "local neighbors" on the same subnet.  The above
> error messages happen when the 64.61.132 network is sending a lot of traffic
> to this machine on its eth1 interface, which in turn emails via the 64.61.133
> network over its eth0 interface.

> One other twist is that both subnets are being processed through the same
> switch, and this is what I'm guessing is making the situation complex.

> The 64.61.132 network has its own separate gateway to the internet, as does
> the 64.61.133 network.  Since both networks operate (independently?) on the
> Level 2 switch, I would assume that this wouldn't be an issue.  But, just
> in case the presence of both ethernet frames on the same switch is the
> cause for all of the ARP confusion, I wanted to mention it.

> So, it basically looks like:

>                      *INTERNET*
>                           |
>     /--------------------------------------------\
>     |                                            |
>    GW to  (64.61.132.233)                       GW to  (64.61.133.26)
>    Internet                                     Internet
>     |                                            |
> |---------|  eth1*------------------*eth0    |---------|
> |64.61.132| ---> |64.61.132.236 eth0| --->   |64.61.133| (mail is sent
> | network |      |64.61.133.26 eth1 | (mail) | network |  from 64.61.133
> |---------|      *--(mail server)---*        |---------|  network)
> (mail originates
>  in 64.61.132 network)

> ifconfig shows:
> eth0      Link encap:Ethernet  HWaddr 00:E0:81:21:DF:7E  
>           inet addr:64.61.133.26  Bcast:64.61.133.31  Mask:255.255.255.248
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:377123 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:251573 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:100
>           RX bytes:81228349 (77.4 Mb)  TX bytes:61257079 (58.4 Mb)
>           Interrupt:11 Base address:0x9000

> eth1      Link encap:Ethernet  HWaddr 00:E0:81:21:DF:7F  
>           inet addr:64.61.132.236  Bcast:64.61.132.239  Mask:255.255.255.248
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:24222 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:137458 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:100
>           RX bytes:1726713 (1.6 Mb)  TX bytes:18298917 (17.4 Mb)
>           Interrupt:10 Base address:0xb000

> lo        Link encap:Local Loopback  
>           inet addr:127.0.0.1  Mask:255.0.0.0
>           UP LOOPBACK RUNNING  MTU:16436  Metric:1
>           RX packets:186847 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:186847 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:0
>           RX bytes:31903076 (30.4 Mb)  TX bytes:31903076 (30.4 Mb)

> Here is what route -n shows:

> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
> 64.61.133.24    0.0.0.0         255.255.255.248 U     0      0        0 eth0
> 64.61.132.232   0.0.0.0         255.255.255.248 U     0      0        0 eth1
> 127.0.0.0       0.0.0.0         255.0.0.0       U     0      0        0 lo
> 0.0.0.0         64.61.133.26    0.0.0.0         UG    0      0        0 eth0

> /etc/sysconfig/network:
> NETWORKING=yes
> HOSTNAME=mail.testing.net
> GATEWAY=64.61.133.26
> GATEWAYDEV=eth0

> This is a redhat 7.3 machine, using kernel 2.4.18-3.

> Does anyone have any suggestions on how to resolve these error messages?
> The network operation does seem to work correctly, but I would like to get
> rid of the constant thrashing of the ARP table so I can avoid these
> messages (and also get rid of the fact that it thinks it needs to keep
> adding all of the mail recipients to its "local neighbors" table).

> Thank you in advance for any help or advice!

> -Raiden

Is the switch capable of supporting VLANS?  If not have you tried
using two seperate layer 2 devices to see if the problem is the
co-existance on the same switch?

Codfather

 
 
 
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1. neighbour table overflow kernel messages

Hi!  I'm usgin RedHat 6.0 w/ a custom 2.2.14 kernel and glibc-2.1.3.
The system has been working fine for a long time and recently I've
started noticing "neighbour table overflow" kernel messages in
/var/log/messages.  Coincidentally, the Apache 1.3.12 server running on
the box is NOT accessible.  It starts just fine and binds to both IPs
(it's a multi-homed machine) on port 80 fine, but when I try to connect
using "lynx" on the Machine itself, I get a "Cannot connect to host"
message and "lynx" terminates.

I'm guessing it's related to the "neighbour table overflow" messages but
I'm not sure.  Any ideas as to what this message means?

My system is a Pentium II-400 MHz w/ 256 MB of RAM.

Any help would be greatly appreciated.

Thanks!

Peace.....

Tom

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