[ale] Meaning of a log message

[Joe Steele]

On Thursday, January 15, 2004 7:50 AM, Cory T. Echols wrote:
>
> Can anyone tell me what these log messages might mean?
>
> Jan 15 04:53:51 localhost kernel: Redirect from 66.30.253.254 on ppp0 about 66.30.243.132 ignored.
> Jan 15 04:53:51 localhost kernel:   Advised path = 66.32.244.12 -> 66.30.243.132, tos 00

The implication is that your box sent a packet to 66.30.243.132 
("Advised path = ...") using 66.30.253.254 as a gateway.  The gateway 
sent back an ICMP Redirect message ("Redirect from ...") saying that 
packets addressed to 66.30.243.132 don't need to be routed through 
66.30.253.254.  Instead, they can be sent directly to 66.30.243.132.

Your box logged the redirect and properly ignored it because ppp0 is 
a point-to-point link, which requires that all traffic via ppp0 can 
only be routed to the gateway at the other end of the link.

When I perform a traceroute to 66.30.243.132, I found that the 21st 
hop is sometimes 66.30.243.132 (2 out of 3 responses), and sometimes 
66.30.243.254 (1 out of three responses):

16  bar02-p2-0.lwllhe1.ma.attbb.net (24.128.190.61)  36.687 ms  37.536 ms  36.851 ms
17  bar02-p6-0.lwrnhe1.ma.attbb.net (24.128.190.58)  37.447 ms  39.496 ms  37.969 ms
18  24.91.0.153 (24.91.0.153)  36.825 ms  36.337 ms  37.311 ms
19  24.128.191.82 (24.128.191.82)  36.656 ms  37.491 ms  37.051 ms
20  24.128.191.46 (24.128.191.46)  37.948 ms  36.703 ms  37.193 ms
21  h0040f439d853.ne.client2.attbi.com (66.30.243.132)  48.013 ms  h0800464e1b0a.ne.client2.attbi.com (66.30.253.254)  115.679 ms h0040f439d853.ne.client2.attbi.com (66.30.243.132)  86.161 ms

Clearly there should only be 1 hop from 24.128.191.46 to 
66.30.243.132, but on occasion 24.128.191.46 routes the packet to 
66.30.253.254 instead.  Apparently when this happens, 66.30.253.254 
sends a ICMP redirect which is coming all the way back to you.

--Joe