[Xorp-users] questions about IPv6 get_link_local_address

XORP at sipxx.com karl at sipxx.com
Fri Oct 9 08:45:12 PDT 2009


Yes, routers must disregard RA messages.

That said, I have found that an xorp router doesn't always do that. If 
the router has two interfaces on a link that gets RAs from another 
router, and only one of them is in the ospf6 configuration, the RA 
received on the second port will still  cause a default route to be set, 
despite the fact that both interfaces are configured in the interfaces 
section and fea-unicast-forwarding is set. For some reason in this case, 
the forwarding flag for the interface doesn't get set but the 'all' flag 
is set.
I think this is a bug, because I would have to enable another routing 
protocol on the port (I presume) to disable the RA. Placing the 
interface in the interfaces section  and having fea->unicast-forwarding6 
set should prevent the acceptance of the RA on all interfaces, IMHO. I 
believe if I manually set the forwarding flag on the second interface, 
RAs are ignored.  This testing was done on a Centos 5.3 virtual machine.

And, yes, all IPv6 stacks allocate the link-local address automatically, 
since it's a required feature for the IPv6 stack to operate fully. 
Regarding the automatic recognition, I can imagine cases were an 
operator may want to assign an address and not use the default provided.



David Balnaves wrote:
> Hi,
>
> Just a quick thanks as I found "default-system-config" addressed my issue
> with setting the link-local address.
>
> All the IPv6 implementations(linux, cisco, windows) I've seen sets a
> link-local address automatically on the interface when the interface is
> brought up.  I think considering this should always be available, having
> XORP OSPFv3 probe for the link local address makes sense.  Its also the
> behaviour of the "other" OSPFv3 implementation for linux.
>
> I've also noticed that since setting "default-system-config", the IPv6
> address assigned to the interface via RA has disappeared.  This may simply
> be because linux IPv6 forwarding has been enabled with XORP OSPFv3 becoming
> active.  I don't recall this happening when I manually set the link-local
> address within XORP(and I dont know how it should deal with this).  From
> what I remember, the RFC states that a "router"  (ie: host with ipv6
> forwarding enabled) should not use addresses provided by RA.
>
> David Balnaves
>
> ----- Original Message ----- 
> From: "XORP at sipxx.com" <karl at sipxx.com>
> To: <xorp-users at xorp.org>
> Sent: Friday, October 09, 2009 10:00 AM
> Subject: Re: [Xorp-users] questions about IPv6 get_link_local_address
>
>
>   
>> That's a reasonable scenario, I suppose. If users need to specify a
>> parameter, they can, and if they use the default-system-config in
>> addition, they get the rest from default.
>>
>> There were some other issues with this parameter from my experimentation.
>> If I have an interface in the configuration file that uses
>> 'default-system-config' and nothing else, it works as expected.
>> But then, if I remove the directive from xorpsh->configure and replace
>> it with an address specification and commit the change, the address does
>> not get configured, I had to save the configuration in a file and
>> restart rtrmgr in order for it to get configured accordingly. This was
>> for an IPv4 address.
>>
>>
>> Ben Greear wrote:
>>     
>>> XORP at sipxx.com wrote:
>>>       
>>>> I am not so sure it really should do this totally automatically just
>>>> because OSPFv3 requires a particular kind of address. So may other
>>>> modules and this can become very non-transparent if each module just
>>>> goes about acquiring its own parameters.
>>>> This what the 'default-system-config' parameter really seems to be
>>>> good for.
>>>> What I would like to suggest however, is to provide additional
>>>> qualifiers to this parameter so one can differentiate what kind of
>>>> system configuration gets imported.
>>>> so for example:
>>>> ....
>>>>     default-system-config {
>>>>        address-link-local-ipv6: true
>>>>        address-link-local-ipv4: false
>>>>        address-ipv4: false
>>>>        address-ipv6: true
>>>>     }
>>>>
>>>>         
>>> How about we just probe for anything not specified by the user?  We
>>> can do the probe
>>> in fea so all of the modules can get the same information.
>>>
>>> Thanks,
>>> Ben
>>>
>>>       
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>>     
>
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