Connectivity issues and packet inspection

[Phil Pennock]

On 2008-06-18 at 20:03 -0400, Steve Bertrand wrote:
> Also, something else I don't quite grasp. I believe it has something to 
> do with source addr selection, but I'm just off to further delve into 
> this now.
> 
> This is a ping from a box to another box ::5 -> ::b6, both within the 
> same prefix /64 (however there is one switch hop to make). The 
> link-local addr is the router on the same prefix. I don't understand why 
> there is an ICMP redirect involved in this situation (ie, why is the 
> router involved at all). Can someone advise what I am missing?
> 
> 19:56:27.669731 IP6 fe80::20b:46ff:fe3e:f341 > 2607:f118::5: ICMP6, 
> redirect, 2607:f118::b6 to 2607:f118::b6, length 160

The first box doesn't have 2607:f118::/64 configured as being on the
local network; if it did, it would be selecting its address on that
network as the source address, instead of using the link-local address
as the source.

Look at the ifconfig output for the box issuing the pings, to confirm
that it seems that it does have an address on that network.  If it
doesn't, you probably need to tell it to accept router advertisements
(or statically configure it, or whatever).

FreeBSD: sysctl net.inet6.ip6.accept_rtadv=1
Linux/various -- normally set up IPv6 to accept RA, AIUI.  Look at
sysctls:
  net.ipv6.conf.all.autoconf = 1
  net.ipv6.conf.all.accept_redirects = 1
  net.ipv6.conf.all.accept_ra = 1
to confirm.

-Phil