[ale] failover planning

[Joe Steele]

On Tuesday, November 30, 2004 8:52 AM, Christopher Fowler wrote:
>
> Not fixed on 2.4.24
>
> I configured the 2nd interface on one of our devices running 2.4.24 as
> 192.168.2.121 and there is no CAT-5 connected.
>
> [cfowler at cfowler cfowler]$ ping 192.168.2.121
> PING 192.168.2.121 (192.168.2.121) 56(84) bytes of data.
> 64 bytes from 192.168.2.121: icmp_seq=1 ttl=64 time=0.405 ms
> 64 bytes from 192.168.2.121: icmp_seq=2 ttl=64 time=0.163 ms
> 64 bytes from 192.168.2.121: icmp_seq=3 ttl=64 time=0.167 ms
>
>
> I guess eth0 on 192.168.2.120 is responding for 192.168.2.121
>

This behavior is controlled by /proc/sys/net/ipv4/conf/*/arp_filter:

arp_filter - BOOLEAN
  1 - Allows you to have multiple network interfaces on the same
  subnet, and have the ARPs for each interface be answered
  based on whether or not the kernel would route a packet from
  the ARP'd IP out that interface (therefore you must use source 
  based routing for this to work). In other words it allows control
  of which cards (usually 1) will respond to an arp request.
 
  0 - (default) The kernel can respond to arp requests with addresses
  from other interfaces. This may seem wrong but it usually makes
  sense, because it increases the chance of successful communication.
  IP addresses are owned by the complete host on Linux, not by 
  particular interfaces. Only for more complex setups like load-
  balancing, does this behaviour cause problems.
 
  arp_filter for the interface will be enabled if at least one of 
  conf/{all,interface}/arp_filter is set to TRUE,
  it will be disabled otherwise

--Joe