On Fri, 20 Aug 2010 19:49:43 -0400 "Ricky Beam" <jfbeam@gmail.com> wrote:
On Fri, 20 Aug 2010 13:20:58 -0400, Christopher Morrow <christopher.morrow@gmail.com> wrote:
Polling a little bit here, there's an active discussion going on 6man@ietf about whether or not v6 routers should: o be required to implement ip redirect functions (icmpv6 redirect) o be sending these by default ... In ipv4 there's a relatively widely used practice of disabling ip redirects.
I think it's almost universally disabled (by default) everywhere in IPv4 purely for security (traffic interception.) In a perfectly run network, redirects should never be necessary, so I'd think IPv6 should avoid going down that road again. (support OPTIONAL, never enabled by default.) [It's another insecure mistake IPv6 doesn't need to repeat.]
You're assuming the cost of always hair pinning traffic on an interface is cheaper than issuing a redirect. Sometimes it won't be. 1 ICMP redirect could result in potentially congestion inducing load being shifted off of a single router's interface. It seems that there might be a common and unstated assumption here that ever router uses hardware forwarding and has high speed 1Gbps+ interfaces that have <50% utilisation. The majority of routers - CPE - don't meet that assumption.
As I recall from long long ago, Cisco IOS would deal with traffic differently depending on redirects... with redirects enabled, a redirect was sent and the packet dropped; with redirects disabled, the router hairpined the packets. I honestly don't know what today's versions do because I've never checked -- A can ping B, I move on. I turn redirects off on *outside* interfaces. Inside (trustable) interfaces vary -- I don't go out of my way to disable them.
--Ricky