Re: Getting "ICMP Host redirect from gateway" response

On 30 May 2007, in the Usenet newsgroup comp.os.linux.networking, in article
<1180514958.395767.101190@xxxxxxxxxxxxxxxxxxxxxxxxxxx>, ianbrn@xxxxxxxxx wrote:

I tried and succeeded in getting a REDIRECT response, but I still have
a little question:
I added a route with 192.168.0.10 as a gateway to a local host
(192.168.0.121). with netmask 255.255.255.255.
192.168.0.10 a linux machine which supports sending redirects and
forwarding.

route -n shows the new entry:
192.168.0.121 192.168.0.10 255.255.255.255 UGH 0 0 0 eth0

I tried PING to 192.168.0.121 and got REDIRECT:

OK

Running traceroute 192.168.0.121 shows that the packets go directly
to 192.168.0.121 and NOT to 192.168.0.10 as a result from this redirect,
as expected. Also following "ping -v 192.168.0.121" does not get
the "HOST REDIRECT" response. However, I expected that the routing table
will be updated as a result and a new entry with the "D" flag will be
inserted, and it did not happen. The routing table stayed the same,
as route -n shows.

I can't say - you'd have to look at the kernel source (depending, this
should be in /usr/src/linux/net/ipv4/* somewhere). I'm not exactly sure
the D flag is implemented in modern kernels. I'd also be looking at the
ARP cache.

There is an example in chapter 9,
"9.5 ICMP Redirect Errors", of "TCP/IP Illustrated - Volume 1
The Protocols" by W. Richard Stevens.

Yes, but what operating system? (Host "solaris" was running am ear;y
version of Solaris 2.2. One of the nice things about "TCP/IP Illustrated"
was that Stevens had a bunch of contemporary systems running various
O/S so you could see the differences. But it was written in 1994, and
Linux wasn't all that common at the time. SLS, Slackware, Yggdrasil,
even an early Debian were available, but that was either an 0.99* or
early 1.0.x kernel.)

Old guy
.

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