I believe I see the distinction. The Router Alert is of particular interest to routers, not all intermediate nodes, and it includes "extra" information about the contents of the packet (outside the Router Alert Option or indeed other options in the H-B-H header).
A H-B-H extension header says "look at the options and perform them", and the Router Alert is a "hint" saying there may be even more interesting stuff in the packet - besides just the options - that requires the router's attention. Spence (hi Brian) >-----Original Message----- >From: Brian McGehee [mailto:[EMAIL PROTECTED] >Sent: Wednesday, November 02, 2005 9:48 AM >To: 'John Spence'; 'Fred Baker' >Cc: ipv6@ietf.org >Subject: RE: Question about the need for a "Router Alert >Option" (RFC 2711)within a Hop-By-Hop Option Extension Header >(RFC 2460) ... > >I like to think of it like this. > >A Router alert is a messaging saying "Hey Routers. You MIGHT >be interested in the body(payload. Other ext headers) of this packet" > >A HBH is a message saying "Hey ALL NODES in transit. You MUST >look in the HBH and do what it says" > >Hope that helps... (hi john) >-Brian >http://consult.tavian.com/ > >-----Original Message----- >From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On >Behalf Of John Spence >Sent: Tuesday, November 01, 2005 7:31 PM >To: 'Fred Baker' >Cc: ipv6@ietf.org >Subject: RE: Question about the need for a "Router Alert >Option" (RFC 2711)within a Hop-By-Hop Option Extension Header >(RFC 2460) ... > > >Sorry - that fired too fast. > >RFC 2711 also references RFC 2460, so it was built for the >H-B-H extension header. Also, if you look at RFC 3810 >(MLDv2), it also references the Router Alert Option and says: > >All MLDv2 messages described in this document MUST be sent >with a link-local >IPv6 Source Address, an IPv6 Hop Limit of 1, and an >IPv6 Router Alert option [RFC2711] in a Hop-by-Hop Options >header. (The Router Alert option is necessary to cause >routers to examine MLDv2 messages sent to IPv6 multicast >addresses in which the routers themselves have no >interest.) > >So, I still don't understand the Router Alert Option, but I >see a number of places where it is referenced. > > > [[Spence]] >________________________________ > > From: John Spence [mailto:[EMAIL PROTECTED] > Sent: Tuesday, November 01, 2005 7:25 PM > To: 'Fred Baker' > Cc: 'ipv6@ietf.org' > Subject: RE: Question about the need for a "Router Alert Option" >(RFC 2711) within a Hop-By-Hop Option Extension Header (RFC 2460) ... > > > Thanks for the quick reply. The Router Alert Option (RFC >2711) is dated October 1999. It says "This memo describes a new >IPv6 Hop-by-Hop Option type ", so the Router Alert is designed >for the H-B-H Extension header. > > > > ---------------------------------------------------- > John Spence, CCSI, CCNA, CISSP > Native6, Inc. > IPv6 Training and Consulting > [EMAIL PROTECTED] > (wk) 206-682-0275 > www.native6.com > ---------------------------------------------------- > > > > > >________________________________ > > From: Fred Baker [mailto:[EMAIL PROTECTED] > Sent: Tuesday, November 01, 2005 6:48 PM > To: John Spence > Cc: ipv6@ietf.org > Subject: Re: Question about the need for a >"Router Alert Option" (RFC 2711) within a Hop-By-Hop Option >Extension Header (RFC 2460) ... > > > one of them sounds like it is redundant. I >think the Router Alert predated the HBH header... > > On Nov 1, 2005, at 6:04 PM, John Spence wrote: > > > Hello; > If the H-B-H >extension header means "all intermediate nodes must look in >here for options to process", why is the "Router Alert" option needed? >As I read the text of the two RFCs, the Router Alert Option is >redundant - just including a H-B-H header means "intermediate >nodes must look at this packet even if it is not addressed to >them", which seems to be the same meaning as Router Alert. > I must be missing >something. Can someone provide a quick answer, or a pointer to >the answer so I can research it myself? > Thanks very much. > John Spence > > > >---------------------------------------------------------------- - >--- > IETF IPv6 working group mailing list > ipv6@ietf.org > Administrative Requests: >https://www1.ietf.org/mailman/listinfo/ipv6 > >---------------------------------------------------------------- - >--- > > > >-------------------------------------------------------------- > "Don't worry about the world coming to an end >today. It's already tomorrow in Australia." (Charles Schulz ) > > > > > > >---------------------------------------------------------------- ---- >IETF IPv6 working group mailing list >ipv6@ietf.org >Administrative Requests: https://www1.ietf.org/mailman/listinfo/ipv6 >---------------------------------------------------------------- ---- -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www1.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
