Subject: forwarding engine and Hinden/Haberman addresses

From: "Aviad Raveh" <[email-masked]>
Date: Thu, 4 Sep 2003 14:26:13 +0200

After reading the Hinden/Haberman ID, I do not understand how does it (if it does) simplify the routing mechanism as described in the “impact of Site-Local addressing” ID, as described in 3.1.2.2:

“First, the forwarding engine on an SBR must look at both the source and destination addresses to determine if either of them is link- local.  If so, the packet will be discarded, as above.  

If the destination is not link-local, it must be either site-local or global. If the destination address is site-local, the router will look at the interface on which the packet was received to determine the site-local zone in which the packet originated, and will perform a lookup in the correct site-local forwarding table and forward the packet, as indicated. 

If the destination address is global, the router will perform a lookup in the global routing table.  It will then use the inbound interface to determine the site-local zone in which the packet originated, and the outbound interface to determine the site-local zone in which the packet will be sent.  If those zones do not match, then the packet is being forwarded across a site boundary. In that case, the router will need to re-examine the source address of the packet to determine if the source is site-local.  If so, the packet will be discarded, and an ICMP "scope exceeded" error message will be generated. Otherwise, the packet will be forwarded, as indicated. 

This processing will need to be performed for every packet that is forwarded by an SBR, and this level of complexity will impact the Impact of Site-Local Addressing in performance, cost and reliability of all IPv6 routers with SBR capability.”

Aviad Raveh

Radlan Computer Communications Ltd.
Atidim Technological Park Bldg #4
Tel Aviv 61131 Israel
Tel:      +972-3-7658909

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From: Margaret Wasserman <[email-masked]>
Date: Thu, 04 Sep 2003 09:47:14 -0400

Hi Aviad,

At 02:26 PM 9/4/2003 +0200, Aviad Raveh wrote:
>After reading the Hinden/Haberman ID, I do not understand how does it (if 
>it does) simplify the routing mechanism as described in the "impact of 
>Site-Local addressing" ID, as described in 3.1.2.2:

Because the Hinden/Haberman prefixes are unique, there is no need
to maintain separate global and local routing tables.  The lookup
can be done in a single forwarding table.

So, it goes like this:

>"First, the forwarding engine on an SBR must look at both the source and 
>destination addresses to determine if either of them is link- local.  If 
>so, the packet will be discarded, as above.

Still required.

>If the destination is not link-local, it must be either site-local or 
>global. If the destination address is site-local, the router will look at 
>the interface on which the packet was received to determine the site-local 
>zone in which the packet originated, and will perform a lookup in the 
>correct site-local forwarding table and forward the packet, as indicated.

No reason to determine the site-local zone and/or to have a separate
local forwarding table.

>If the destination address is global, the router will perform a lookup in 
>the global routing table.  It will then use the inbound interface to 
>determine the site-local zone in which the packet originated, and the 
>outbound interface to determine the site-local zone in which the packet 
>will be sent.  If those zones do not match, then the packet is being 
>forwarded across a site boundary. In that case, the router will need to 
>re-examine the source address of the packet to determine if the source is 
>site-local.  If so, the packet will be discarded, and an ICMP "scope 
>exceeded" error message will be generated. Otherwise, the packet will be 
>forwarded, as indicated.

There are no zones, so there is no need to determine if a packet with
a local source address will cross a zone boundary.

Administrators _may_ choose to filter packets to/from local addresses
(or to/from any other addresses) at administratively-defined boundaries,
but that can be handled through a straightforward filter.

Margaret