On 1-okt-04, at 2:48, Dean Anderson wrote:
Note though that it's *very* hard to create a setup where packets are
delivered to different multicast instances, as it's hard to imagine how
any real-world anycast setup could match the criteria in
Its quite easy for anycast: (real names used, but not real relationships)
Av8
/ \
sprint att
\ /
F-root
If Av8 turns on PPLB, traffic to F-root will go through both sprint and att on a per-packet basis.
No, that won't happen because in order for BGP to install multiple paths in the routing table, the following conditions must be met:
"To be candidates for multipath, paths to the same destination need to have the following characteristics equal to the best path's characteristics:
[...]
â One of the following:
â Neighboring AS or sub-AS (before the eiBGP Multipath feature was added)
â AS-PATH (after the eiBGP Multipath feature was added)"
(From the URL I cited in my previous message.)
In this case either of the sub-conditions won't be met.
Per packet load balancing is inappropriate in cases where the entire path is different, as the limitations of the inferior path are imposed on the full set. BGP has enough knobs to distribute the load without this anyway. FIB-based load balancing is only appropriate when a small part of a single path is populated with more than one physical link. And in most of those cases, load balancing mechanisms that make sure one flow runs over one link are more desirable. Only in cases where this leads to a significantly unbalanced traffic distribution, per packet load balancing is a good idea. (But even then most people don't enable it as they are (too, IMO) afraid of packet reordering.)
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