kern/166462: gre(4) when using a tunnel source address from carp(4) doesn't honor the MASTER/BACKUP state

[Eugene M. Zheganin]

>Number:         166462
>Category:       kern
>Synopsis:       gre(4) when using a tunnel source address from carp(4) doesn't honor the MASTER/BACKUP state
>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:   Wed Mar 28 05:40:09 UTC 2012
>Closed-Date:
>Last-Modified:
>Originator:     Eugene M. Zheganin
>Release:        8.2-RELEASE
>Organization:
RealService LLC
>Environment:
FreeBSD moscow-omega 8.2-RELEASE FreeBSD 8.2-RELEASE #5: Sat Mar 10 14:15:00 MSK 2012     emz at moscow-omega:/usr/obj/usr/src/sys/MOSCOW  amd64
>Description:
When using a HA system of two nodes for corporate VPN I encountered a problem:

Imagine node A and B share the same public ip address on their carp(4) interface.
Imagine A and B have a gre(4) interface, and its tunnel source address is the carp(4) address.
Imagine there is an ospf daemon running on those gre(4) interfaces.

Then the OSPF neiborship will be constantly reestablished, because A and B will interfere with OSPF sessions of each other.

This happens because both nodes will send a HELO packet, and the backup node isn't honoring its BACKUP state properly.
>How-To-Repeat:
Build a setup mentioned above. Use OSPF or just try to send icmp packets via the tunnel from the BACKUP node.
>Fix:
Use IPSEC with 'required' policies. This will prevent the backup node from establishing SA, thus preventing the tunnel from working.

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