Arp timeout

Arp timeout

Post by Guy Rodesc » Sat, 02 Oct 1999 04:00:00



Hello,

When we change the interfaces card of a router of our network, the UNIX
machines take a very long time or endless time to change the ARP table
buffer with the new MAC address of the router. Is there a way that UNIX
boxes react dynamically to the new situation, that the MAC address of an
IP address has changed?

Any help would be appreciated,
Thanks a lot,
Guy.

 
 
 

Arp timeout

Post by Barry Margoli » Sat, 02 Oct 1999 04:00:00




Quote:>When we change the interfaces card of a router of our network, the UNIX
>machines take a very long time or endless time to change the ARP table
>buffer with the new MAC address of the router. Is there a way that UNIX
>boxes react dynamically to the new situation, that the MAC address of an
>IP address has changed?

It should notice it immediately.  Most systems (including routers) send out
a gratuitous ARP broadcast when an interface is enabled or updated, and
this should update all ARP caches on the network.  Also, when the router
needs to communicate with a machine on the LAN it will send out ARP
broadcasts, which should update the ARP caches on any machines that missed
the gratuitous ARP.

--

GTE Internetworking, Powered by BBN, Burlington, MA
*** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.

 
 
 

Arp timeout

Post by Andrew Gabri » Sat, 02 Oct 1999 04:00:00




Quote:>Hello,

>When we change the interfaces card of a router of our network, the UNIX
>machines take a very long time or endless time to change the ARP table
>buffer with the new MAC address of the router. Is there a way that UNIX
>boxes react dynamically to the new situation, that the MAC address of an
>IP address has changed?

If you can persuade the router to broadcast an ARP response
(and the unix boxes exactly implement RFC826, which I suspect
they do), the change should be noticed immediately, even though
they didn't ask. I suppose you could generate this ARP
response broadcast from anywhere - it doesn't have to come
from the router, but short of knocking up a special program, I
don't know of anything existing which can do it.

You could use arp -d to delete the incorrect entry manually, but
would have to run this on all systems.

--
Andrew Gabriel
Consultant Software Engineer

 
 
 

1. ARP Timeout

Hello,

I am experimenting with a diskless setup between two computers.
It works when the client has a pci network interface card but fails
when I try to use an integrated lan in the client. I am using
tftpd-hpa to transfer the kernel. The process gets as far as
transferring the IP addresses via dhcp but stops at the kernel transfer
with an error message, "PXE E11 ARP timeout". I tried tcpdump, and it
gets as far as the line, repeated 8 times,

0:e0:4c:7c:d9:eb ff:ff:ff:ff:ff;ff 0806 60: arp who-has 192.168.1.5 \
  tell 192.168.1.10

I don't know how to fix this. I tried the command on the server,

# arp -s 192.168.1.5 00:03:47:ff:47:ad
SIOCSARP: Invalid argument

Presumable it fails because I cannot identify the server's own hardware
address on the server itself. However, I don't really know. Do I need a
third computer as an arp server, or am I missing something?
Thanks for any help.

Bob Parnes

--
Bob Parnes

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