kern/123881: Turning on TCP blackholing causes slow localhost connections

[Tom Karpik]

>Number:         123881
>Category:       kern
>Synopsis:       Turning on TCP blackholing causes slow localhost connections
>Confidential:   no
>Severity:       serious
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Wed May 21 23:20:01 UTC 2008
>Closed-Date:
>Last-Modified:
>Originator:     Tom Karpik
>Release:        7.0-RELEASE
>Organization:
>Environment:
FreeBSD OsirisBSD 7.0-RELEASE FreeBSD 7.0-RELEASE #0: Sun Feb 24 19:59:52 UTC 2008     root at logan.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC  i386
>Description:
Turning on TCP blackholing (sysctl net.inet.tcp.blackhole=2) seems to make connecting to some local services very slow.

Example: telnet localhost 25 (default local Sendmail daemon after fresh installation of FreeBSD)

Sendmail responds with its greeting string right away if blackholing is off. If it's turned on, it takes about 8-12 seconds for the greeting to show up.
>How-To-Repeat:
sysctl net.inet.tcp.blackhole=2 (or 1)
telnet localhost 25
>Fix:
sysctl net.inet.tcp.blackhole=0

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