kern/123991: ECMP balancing issues

[Barrett Lyon]

>Number:         123991
>Category:       kern
>Synopsis:       ECMP balancing issues
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Mon May 26 01:00:08 UTC 2008
>Closed-Date:
>Last-Modified:
>Originator:     Barrett Lyon
>Release:        8.0-CURRENT
>Organization:
>Environment:
FreeBSD home.blyon.com 8.0-CURRENT FreeBSD 8.0-CURRENT #3: Sun May 25 02:18:13 PDT 2008     blyon at home.blyon.com:/usr/obj/usr/src/sys/GENERIC  i386

CVSUP as of May 25th


>Description:
Using RADIX_MPATH support in the kernel provides the desired ECMP support, however ECMP does not appear to load balance properly.

The first route appears to be a primary route, were the second path becomes almost a backup route.  Removing the first and re-adding it causes the preference to swap.

This is also seen in the netstat -rn "Use" output, where the counter on the => route is always higher than the secondary route.

The destination IPs are very mixed.

The desired effect would be a better load distribution across the two next-hops or even per-packet load balancing as an option.
>How-To-Repeat:
Add two routes with different next-hops, the first route becomes the preference route.
>Fix:
none

>Release-Note:
>Audit-Trail:
>Unformatted: