-----Original Message----- From: Jared Mauch [mailto:ja...@puck.nether.net] Sent: Friday, August 13, 2010 5:34 PM To: Hemant Singh (shemant) Cc: Randy Bush; ipv6 deployment prevention Subject: Re: Router redirects in Node Requirements document
>Been typing during breaks in a 300+ mile trip. I was more speaking to the adverse impacts of v4 redirects BUT..... >Unless you think there is some awesome reason that people are going to need redirects that have multiple routers on the shared lan WITH hosts that are not speaking some dynamic routing protocol with >said routers, redirects are unnecessary and promote bad architecture. If that is your goal, then I would understand what is going on here. I've seen a lot of poorly architected networks that have nearly >broken or melted down due to abusing something that is feasible in this space. >I'm not sure what the true use case is for redirects here. Again, sorry to be a nag but such a question should have been raised when RFC 2461 or RFC 4861 were being discussed in the IETF. The Node-Req document is only putting in text for what is already agreed upon in an RFC like the RFC 4861. I suppose the community did find a need for Redirect and that is why this functionality was added to IPv6 ND. However, here is one use case and let anyone else chime from the RFC 2461 and RFC 4861 development days for more use cases. Indeed a multiple router deployment begs the need for Redirect. The other deployments where Redirect is necessary is where hosts acquire addresses via DHCPV6. DHCPv6 does not dole out prefix length with the IPv6 address. So the host does not know what destination is on-link to the host. Therefore, the host would send packets to the default router(s). Since the router knows what destination is on-link, the router can issue Redirects. For example, see this cable modem deployment. Two hosts are sitting behind a bridged cable modem. A switch behind the cable modems connects the two hosts. Each host acquires a global IPv6 address using DHCPv6 and the cable access concentrator (a CMTS - cable modem termination system) serving the cable modem sent an RA to the modem and the hosts with no PIO (Prefix Information Option). Such a RA signals to the hosts to send traffic to the default router (the CMTS). Now host, H1 sends traffic destined to host, H2 to the CMTS. During DHCPv6, the CMTS DHCPv6 relay agent gleaned the fact that H2's is using a cable modem, CM1 (based on L2 cable control that uses a Service ID, SID). Likewise, the CMTS also knows H1 is behind CM1. So when a packet sent from H1 destined for H2 arrives at the CMTS (also the first hop IPv6 router), the CMTS issues a Redirect to H1 to communicate directly with H2. Therefore, I am still for what Brian Carpenter suggested. Here is proposed new text for Redirect. "Redirect functionality SHOULD be supported. If the node is a router, Redirect functionality MUST be implemented and SHOULD be enabled by default." Hemant -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
