[Xorp-users] OLSR route redistribution in XORPv1.5

[Bruce M Simpson]

Sproat, Jackalynn wrote:
> I just wanted to clarify what you meant by:
>
> "... experiment with the syntax for the various 
> tags in etc/templates/olsr4.tp... to filter various 
> announcements if going in the opposite direction (OLSR to OSPF or other 
> protocol)."
>
> Why can't I just define an export policy similar to "ospf-to-olsr", but
> in the opposite direction?

You certainly can, but as with all routing protocols, information 
present in one might not be desired to be present in the other, which is 
why the policy tags mechanism exists.

For example if you exported all the N1/N2 topology in a highly mobile 
environment, this might cause a lot of unnecessary route updates to be 
propagated into the protocol you are redistributing into, and with the 
policy you provided, that is what would happen.

i.e. every time a one-hop or two-hop neighbour changed link status, this 
would cause an OSPF LSA to be advertised upstream with the E bit set, 
and if you are not redistributing into a stub area, that's a lot of 
route updates just because someone moved their laptop.

Currently there is no hysteresis mechanism for this, nor any means of 
automatically inferring an aggregate prefix (all IPv4 OLSR node routes 
are /32), as nobody has needed it yet.



>  For example:
>
> %%%
> protocols {
>  ospf4 {
>   ...
>   export: "olsr-to-ospf"
>   ...
>  }
> }
>
> policy {
>  ...
>  policy-statement olsr-to-ospf {
>    term a {
>      from {
>        protocol: "olsr"
>      }
>      then {
>        accept
>      }
>    }
>  }
>  ...
> }
> %%%
> Cheers,
> Jackie
>
> -----Original Message-----
> From: Bruce M Simpson [mailto:bms at incunabulum.net] 
> Sent: Monday, September 08, 2008 11:29 AM
> To: Sproat, Jackalynn
> Cc: xorp-users at xorp.org
> Subject: Re: [Xorp-users] OLSR route redistribution in XORPv1.5
>
> Sproat, Jackalynn wrote:
>   
>> Hello,
>>
>> I am new to XORP and am interested in redistributing routes between 
>> XORP OLSR and XORP OSPF.
>>
>> At www.mail-archive.com/xorp-hackers at icir.org/msg00413.html
>> <file://www.mail-archive.com/xorp-hackers@icir.org/msg00413.html> it 
>> was mentioned that CenGen had success with exporting inot OSPF in 
>> their testbed.  I was just wondering how I can get more information 
>> w.r.t to doing the same.  For example, is this a simple as including 
>> the statement export ospf on the OSLR router? Where in the .boot file 
>> should this statement be inserted?
>>
>>     
>
> The OLSR implementation is a standard XORP routing process, which 
> supports route redistribution using the standard mechanisms, and uses a 
> similar syntax as the other processes (BGP, RIP etc).
>
> You need to define an export policy and include it like this:
>
> %%%
> protocols {
>  olsr4 {
>   ...
>   export: "ospf-to-olsr"
>   ...
>  }
> }
>
> policy {
>  ...
>  policy-statement ospf-to-olsr {
>    term a {
>      from {
>        protocol: "ospf"
>      }
>      then {
>        accept
>      }
>    }
>  }
>  ...
> }
> %%%
>
> Currently the OLSR redist support doesn't allow you to specify a metric,
>
> as this isn't part of the OLSRv1 spec. ETX link metrics aren't supported
>
> however this support could be added at a later date if there is further 
> interest.
>
> Also, the policy tags/varmap which xorp_olsr uses are not currently 
> documented. You can try experimenting with the syntax for the various 
> tags in etc/templates/olsr4.tp. These can be used to filter various 
> announcements if going in the opposite direction (OLSR to OSPF or other 
> protocol).
>
> For docs, see docs/olsr. You'll need LaTeX installed to build PDFs of 
> the OLSR documentation.
>
> thanks
> BMS
>
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> Thank you. 
>
>